CCNP Concepts Flashcards
1
Q
How do you configure BGP with a loopback?
A
Use the neighbor 10.0.0.2 update-source command. Without the neighbor update-source configuration command, the TCP session will use the IP address of the outgoing physical interface and the neighbor will reject the incoming TCP SYN packet as it’s not coming from a recognized BGP neighbor.
2
Q
What do you have to add in OSPF to ensure route redistribution works?
A
You must add the subnets parameter otherwise OSPF will ONLY advertise networks.
3
Q
Does an implementation plan require the detailed configuration changes to be made?
A
It may seem trivial for simple implementations, but Cisco requires that any network implementation plan includes documentation that shows what changes will be made to the current configurations. When performing more complex implementations in a production environment, having a well though-out implementation plan reduces the downtime and is very important – just make sure you also include the actual configuration change steps!
4
Q
Explain route map logic.
A
- If you use an ACL in a route-map permit clause, routes that are permitted by the ACL are redistributed.2. If you use an ACL in a route-map deny clause, routes that are permitted by the ACL are not redistributed.3. If you use an ACL in a route-map permit or deny clause, and the ACL denies a route, then the route-map clause match is not found and the next route-map clause is evaluated
5
Q
Which router command will allow an administrator to configure the administrative distance of a redistributed routing protocol?
A
The distance command will manually change the AD value for specific network prefixes.
The syntax is distance {ip-address {wildcard-mask}} [ip-standard-list] [ip-extended-list]
router rip
distance 125 10.10.10.2 0.0.0.0
6
Q
What special type of IPv6 address does ::/0 represent?
A
A: ::/0 is the default route in IPv6
The address ::/0 is the IPv6 equivalent of “any”, which is why it is used as the default route address. It is the equivalent of 0.0.0.0/0 in IPv4.
An example IPv6 static default route configuration would look like this:
RouterA(config)# ipv6 route gig0/1 ::/0 10.10.10.2
7
Q
What are the two ways a BGP router can advertise its networks?
A
A: A BGP router can advertise its networks using the network statement or the aggregate-address command.
BGP uses network statements to define which networks the local router should advertise. Each network doesn’t have to be originating from the local router, but the network must exist in the routing table. The optional mask keyword is often recommended as BGP supports subnetting and supernetting.
The aggregate-address command can be used to aggregate (or summarize) BGP routes. The aggregate network is then advertised to a router’s BGP neighbor in the same way the network command does – only it contains a larger network that includes many smaller BGP networks.
8
Q
Which three OSPF LSA types describe subnet information that can be used when calculating routes within OSPF?
A
A: LSA Type 1, 2, and 3
LSA Types 1, 2, and 3 all are used for calculating the best cost to inter-OSPF routes. LSA Types 4, 5, and 7 are used for calculating the best cost to routes outside of OSPF – those redistributed by another routing protocol.
9
Q
True or False:When EIGRP detects a topology change, it sends an update to all of its neighbors with only the changes in the update.
A
A: False
EIGRP sends updates to only to the routers affected by the change, not all of its neighbors. One of EIGRP’s many benefits is that it uses partial triggered updates to its directly connected neighbors rather than periodically sharing its entire routing table. This saves link bandwidth because:
- Updates are only sent if a change is incurred
- Only the changes are sent in the update
- Updates are only sent to a routers’s affected neighbors
10
Q
An administrator issues the command aggregate-address 192.168.0.0 255.255.252.0 on a BGP router peered with other BGP speakers. They peers do not receive the aggregate network advertisement however. What is most likely the cause?
A
A: The configured router does not have any 192.168.0.0/22 subnets in its BGP routing table.
The aggregate-address mask command allow an administrator to summarize specific routes into a single aggregate route. Aggregation applies only to routes present in the BGP routing table however. If one or more routes within the aggregate address exist in the BGP routing table, aggregation will be performed.
This is different from the BGP network command, which applies to routes within the local IP routing table.
11
Q
The following configuration has been applied to redistribute OSPF into EIGRP. What does the value of 1000 represent?
router eigrp 1
redistribute ospf 1 metric 1000 100 255 1 1500
A
A: The 1000 value in the redistribute command represents a bandwidth value of 1000Kbps, or 1Mbs.
The metric subcommand under EIGRP assigns values to all routes redistributed in to the routing protocol (EIGRP in this case). Different routing protocols use differenet and incompatible metrics to determine the trustworthiness of their routes. When redistribution is performed, a standard set of metrics must be used for the external routes being imported.
In this example, the values represent 1000Kbs of bandwidth, 1000 microseconds of delay (always need to multiply this by ten), a load of 255, a reliability of 1, and 1500 for the MTU.
12
Q
RouterA and RouterB are EIGRP neighbors. RouterA needs to receive routes from RouterB, but not advertise any routes to RouterB. What would better solve the requirements on RouterA – the passive interface command or using a distribute list?
A
A: A distribute list would be the best technique to meet the question’s requirements
First, the passive-interface command would not meet the requirements. If the passive-interface command was applied, the neighbor relationship would end because it blocks hellos from being exchanged.
Distribute lists are designed to solve exactly the type of requirements the question presents. They filter what routes are advertised or received.
In this case, a configuration similiar to the following would meet the requirements:
access-list 10 deny any ! router eigrp 100 distribute-list 10 out FastEthernet 0/1 !
13
Q
What dynamic routing protocol allows an administrator to control how much bandwidth is used for routing protocol control information over a low-speed hub-and-spoke Frame Relay topology
A
A: EIGRP
By default EIGRP will use up to 50% of a link’s bandwidth for control information. EIGRP can however be configured to only use a specific amount of control-plane bandwidth over the link.
In situations where a hub-and-spoke Frame Relay design is used with lower a low CIR (like 64 kb/s), EIGRP can be configured with the actual CIR value – not just the default serial interface’s physical bandwidth (1544 kb/s). This makes EIGRP a popular choice in legacy, slow speed Frame Relay networks.
An example might look like:
R1 (config)# interface serial 0/0/0
R1 (config-if)# bandwidth 64
R1 (config-if)# exit
14
Q
What two types of routes do EIGRP stub routers advertise?
A
A: Summary and connected routes
A router that is configured as a stub with the eigrp stub command shares connected and summary routing information with all neighbor routers by default.
This can be verified in the output of the show ip eigrp neighbor detail command on the hub router (connected to the spoke/stub router).
15
Q
Based on the OSPF redistribution configuration below, what is the effect of the external 2 parameter?
A
A: The external 2 parameter adds an extra match condition to the redistribution – looking elusively for OSPF E2 routes.
In this case, only OSPF E2 routes coming from OSPF process ID 1 will be redistributed onto the OSPF 20 process.
router ospf 20
redistribute ospf 1 external 2
16
Q
True or False: The IPv6 header is 40 bits long.
A
A: False, the IPv6 header is 40 bytes long
All IPv6 addresses are 128 bits long and contain a fixed-length 40-byte header. Understanding the feilds contained within the IPv6 header is important. Remember that version, traffic class, flow label, payload length, next header, hop limit, SA, and DA are all fields contained within the IPv6 header.
17
Q
What technique when applied to a router at the boundary of an IPv4 network and an IPv6 network would allow a IPv4-only and IPv6-only hosts to communicate?
A
A: NAT-PT
Network Address Translation – Protocol Translator (NAT-PT) allows IPv4 devices to communicate with IPv6 devices without running a dual stack requirement on end hosts. NAT-PT allows bidirectional translation services.
18
Q
Define the MAC address of the multicast IP address 239.255.0.11?
A
A: 0100:5E7F:000B
When converting multicast IP addresses to their corresponding MAC address, simply keep the following rules in mind.
- The MAC address for multicast addresses always begins with 0100:5E.
- The remaining hex values are derived from the last 23 bits in the IP address.
In this case, we break the 255 octet in half to 127 (7F in hex). The third octet of 0 is 00 in hex. The last octet of 11 is 0B in hex.
19
Q
An update has been made to the BGP ingress routing policy. Which BGP feature should be used used to process the update while avoiding high memory utilization on the router?
Will BGP apply changes to the routes it already has?
What is another way to do this?
A
A: Route refresh
Internet routers running BGP have enormous routing tables. When a filter is applied, like a route map, changes to BGP attributes occur. Those changes could affect many of the routes already in the routing table from BGP. Because BGP’s network list is usually very long, applying a route map or prefix list after BGP has converged can be disastrous. The router would have to check the filter against every possible route and attribute combination.
To make matters worse, if it were to apply the filters and pull routes back from neighbors, those changes could then cause another reconvergence – and on and on. In an effort to avoid that scenario (BGP loves stability), BGP will only apply attribute and network changes to routes AFTER the filter has been applied. All existing routes stay unchanged.
There are two ways to reset the BGP session without resetting the TCP sessions between all peers: route refresh or soft-reconfiguration.
When a route refresh is perfomed, the BGP router requests its remote peers to resend its BGP Adj-RIB-Out. This allows the BGP router to reapply the inbound policy without any added memory overhead on the local router.
Soft-reconfiguration stores all received (inbound) routing policy updates without modification in a table so that when a new filter is applied, the router will use this table to calculate the changes without resetting the TCP session between the two BGP peers. This is extremely memory intensive and not recommended by Cisco.
20
Q
The show ip ospf database external shows what type of LSAs?
A
A: Type 5 LSAs
The show ip ospf database external command displays information about external LSAs (Type 5 LSAs) only.
OSPF uses the Type 5 external link LSAs to advertise external routes originated from an ASBR. They are flooded through the OSPF domain and directs packets for those external addresses to the ASBR.
21
Q
DOCSIS is the international standard for transmitting data over what type of system?
A
A: Cable
DOCSIS, or Data Over Cable Service Interface Specification, is is an international telecommunications standard that enables high-speed data transfers over traditional cable TV networks. It is used commonly by cable TV providers to deliver internet connectivity to home and businesses over coax.
22
Q
What three parts make up a complete and functional Cisco IP SLA operation?
A
A:
- The operation number
- The operation definition
- The operation schedule (start time)
All three parts are required for a Cisco IP SLA operation to function. A short example with each requirement on one line would be:
ip sla 20
icmp-echo 10.20.1.1
ip sla schedule 20 start-time now life forever
23
Q
What would be the result if two OSPF routers were directly connected over a shared segment and the priority on both were set to 0?
A
A: Both routers would remain stuck in the two-way state
For proper OSPF exchange to take place over a share segment, a DR and BDR must be elected. Since both routers in this example have their OSPF priority set to 0, neither can become the DR and therefore the OSPF exchange will stop.
OSPF Elections
1. When the OSPF process on a router starts up, it listens for hellos. If it does not receive any within its dead time, it elects itself the DR.
- If hellos are received before the dead time expires, the router with the highest OSPF priority is elected as the DR. Next, the same process happens to elect the BDR. Note: If a router’s OSPF priority is set to 0, it will not participate in the elections.
- If two routers happen to have the same OSPF priority, the router with the highest Router ID will become DR. The same is true for BDR.
24
Q
RouterA needs to establish a BGP neighbor relationship with RouterC in a way that allows failover if either RouterB or RouterD goes down. How can this be accomplished? (Non fully meshed square)
A
A: Configure loopback interfaces on RouterA and RouterC and use them in the BGP update-source command.
Instead of using one physical interface to establish a TCP connection to a BGP peer, loopbacks on each router can be used to establish the connection. This decouples the TCP/IP connection from a single physical interface, allowing link redundancy.
RouterA: interface loopback0 ip address 1.1.1.1 255.255.255.255 ! router bgp 65001 neighbor 2.2.2.2 remote-as 65001 neighbor 2.2.2.2 update-source loopback0
RouterC: interface loopback0 ip address 2.2.2.2 255.255.255.255 ! router bgp 65001 neighbor 1.1.1.1 remote-as 65001 neighbor 1.1.1.1 update-source loopback0
25
True or False: When a system is running in dual stack mode, the IPv6 stack has a dependency on the IPv4 stack to operate.
A: False
IPv4 and IPv6 can run on the same host or system with no dependency on each other to function. When both IPv4 and IPv6 are run in parrallel, it is refered to as a dual stack arcitecture. As organizations begin to migrate their networks to IPv6, dual stack can be used to transition those hosts that support it.
Dual Stack Benefits
1. IPv4 and IPv6 can run independent of each other
2. Dual stack removes the IPv6-in-IPv4 tunneling requirement
3. Dual stack allows a slower, managed migration off of IPv4
Out of all of the IPv6 migration strategies, dual stack is often preferred. Since the end devices can speak to each other in either IPv4 or IPv6 natively, either can be used.
Perhaps the best part? The protocol choice can be controlled in DNS. The transmitting host will send IPv4 packets if it receives an IPv4 address from the DNS server (known as an A record) or IPv6 packets if it receives an IPv6 address from DNS (known as an AAAA record).
Changing which hosts uses which IP protocol can simply be a matter of updating the DNS A or AAAA record.
26
RouterA, an ABR between area 0 and area 2, has routes in area 2 for 10.20.1.0/24 and 10.20.2.0/24. 10.20.1.0/24 has a metric of 16 and 10.20.2.0/24 has a metric of 34. If the statement shown below is added to the running configuration of RouterA, what new route will be advertised into area 0?
A: RouterA will advertise a route to 10.20.0.0/16 into area 0 with a metric of 16
The area 2 range 10.20.0.0 255.255.0.0 command creates a summary route for the 10.20.0.0/16 network. By default OSPF summary routes use the metric of the lowest metric route as its own (16 in this case).
Note also that RouterA will stop advertising routes to the 10.20.2.0/24. and 10.20.1.0/24 networks into area 0.
27
Router R1 has been recently configured for EIGRP MD5 authentication, but it appears that the EIGRP packets are being dropped by R1′s neighbors. The password has been double-checked to match the other routers. What should be changed in the configuration below?
R1(config)# key chain SECURE
R1(config-keychain)# key 1
R1(config-keychain-key)# key-string daffy
R1(config-keychain-key)# exit
R1(config)# interface gig 1/2
R1(config-if)# ip authentication mode eigrp 10 md5
A: The interface subcommand ip authentication key-chain eigrp 10 SECURE is missing
EIGRP supports authentication of its messages using an MD5 hash. When configured, if an incoming EIGRP packet’s hash does not match the local hash, the packet is silently dropped.
Authentication configuration steps:
1. Configure a key chain to group the keys.
2. Create a key(s) inside the keychain. The router will look inside the keychain and compare the keys against incoming packets.
3. Enable authentication and assign a key to an interface.
4. Indicate MD5 as the authentication type.
Based on the these steps, the complete configuration should look like this:
R1(config)# key chain SECURE
R1(config-keychain)# key 1
R1(config-keychain-key)# key-string daffy
R1(config-keychain-key)# exit
!
R1(config)# interface gig 1/2
R1(config-if)# ip authentication mode eigrp 10 md5
R1(config-if)# ip authentication key-chain eigrp 10 SECURE
28
What are two common checks that should be performed when external routes being redistributed into OSPF are not in the OSPF database?
1. Check that the subnets keyword is being used in the redistribution statement.
2. Check that the ASBR router is not redistributing the external routes into a totally stubby area.
The subnets keyword at the end of the redistribute command is extremely important of you are redistributing subnets. Without this keyword, OSPF will redistribute networks at their classful boundaries – in effect dropping the specific routes from ever reaching the OSPF database.
Totally Stubby Areas do not accept any external routes from non-OSPF sources and they do not accept routes from other areas within their OSPF autonomous system.
29
How is bandwidth distributed with EIGRP on a pure multipoint (no subinterface) NBMA network?
How do you avoid overloading?
In this configuration EIGRP will divide the configured bandwidth evenly across each virtual circuit. You must ensure that this will not overload each virtual circuit. For example, if you have a T1 access line with four 56K VCs, you should configure the bandwidth to be 224Kbps (4 * 56Kbps) in order to avoid dropping packets. If the total bandwidth of the virtual circuits equals or exceeds the access line speed, configure the bandwidth to equal the access line speed. Note that if the virtual circuits are of different capacities, the bandwidth must be set to take into account the lowest capacity virtual circuit.
For instance, if a T1 access line has three 256Kbps VCs and one 56Kbps VC, the bandwidth should be set to 224Kbps (4 * 56Kbps). In such configurations, putting at least the slow virtual circuit onto a point-to-point subinterface is strongly recommended (so that the bandwidth can be raised on the others).
30
How is bandwidth distributed for EIGRP on a Pure Point-to-Point Configuration (Each VC on a Separate Subinterface)?
This configuration allows maximum bandwidth control, since the bandwidth can be configured separately on each subinterface, and is the best configuration if the virtual circuits have different capacities. Each subinterface bandwidth should be configured to be no greater than the available bandwidth on the associated VC, and the total bandwidth for all subinterfaces cannot exceed the available access line bandwidth. If the interface is oversubscribed, the access line bandwidth must be divided across each of the subinterfaces. For instance, if a T1 access line (1544 Kbps) has ten virtual circuits with a capacity of 256Kbps, the bandwidth on each subinterface should be configured to be 154Kbps (1544/10) instead of 256Kbps each.
31
What are the three NBMA (nonbroadcast multiple access) scenarios for EIGRP?
There are three different scenarios for NBMA interfaces.
Pure Multipoint Configuration (no subinterfaces)
Pure Point-to-Point Configuration (each VC on a separate subinterface)
Hybrid Configuration (point-to-point and multipoint subinterfaces)
32
Answer the following for each:
Must manually define neighbors?
Must elect a DR/BDR?
Must allow pseudo broadcast?
RFC 2328-compliant modes:
Nonbroadcast (NBMA)
Point-to-multipoint
Cisco additional modes:
Point-to-multipoint nonbroadcast
Broadcast
Point-to-point
RFC 2828 compliant modes:
Nonbroadcast:
Must manually define neighbors? Yes
Must elect a DR/BDR? Yes
Must allow pseudo broadcast? No
Point-to-multipoint:
Must manually define neighbors? No
Must elect a DR/BDR? No
Must allow pseudo broadcast? Yes
Cisco additional modes:
Point-to-multipoint nonbroadcast:
Must manually define neighbors? Yes
Must elect a DR/BDR? No
Must allow pseudo broadcast? No
Broadcast:
Must manually define neighbors? No
Must elect a DR/BDR? Yes
Must allow pseudo broadcast? Yes
Point-to-point:
Must manually define neighbors? No
Must elect a DR/BDR? No
Must allow pseudo broadcast? N/A
Page 3-56 in global knowledge book.
33
What is the MED (Multi Exit Discriminator) attribute in BGP?
Is lower or higher preferred?
MED is an optional nontransitive attribute. MED is a hint to external neighbors about the preferred path into an autonomous system (AS) that has multiple entry points. The MED is also known as the external metric of a route. A lower MED value is preferred over a higher value.
34
Wich dynamic IPv6 tunnel type uses 0×2002 for the first two bytes of the IPv6 address and the hexadecimal equivalent of the IPv4 address for the remaining four bytes?
A: 6to4 tunnels
6to4 tunnels are similar to the manual tunnel, but set up the tunnel dynamically.
6to4 tunnels use 2002::/16 IPv6 addresses in front of the 32 bit IPv4 address of the edge router – creating a 48 bit prefix. Each router on both sides of the tunnel needs a route to its peer. They only support static and BGP routes, so be careful.
35
True or False:When an EIGRP router successor router is removed and a FS exists, the neighbor adjacency is removed then DUAL is notified of the change.
A: False
When an EIGRP router successor router is removed and a FS exists, the router goes through a series of processes to transition from the successor route to the feasible successor route. The process is as follows:
1. DUAL is notified of the topology change
2. The neighbor adjavency is removed
3. All topology entries learned from that neighbor are removed
4. The FS route is used
All of these steps occur very quickly, allowing EIGRP to dynamically transition the route to the feasible successor with limited network interruption.
36
What special type of IPv6 address does ::/128 represent?
A: ::/128 represents the IPv6 unspecified address
::/128, which corresponds to 0.0.0.0/32 in IPv4, is referred to as the unspecified address due to its use of all zeros. The unspecified address is used by applications that need to listen on a particular port or interface for incoming connections. It should never be assigned to a host or router interface.
37
Why would you configure a Cisco router as a PPPoE client?
A: For DSL internet service provider connectivity.
DSL uses the protocol PPP over Ethernet to transfer information between the end client and the provider equipment. Either the end host (like a PC) can be configured with the appropriate PPPoE client software or the local router can be configured to terminate the connection. If the router is used, it can decapsulate the frames and forward them on to end hosts as traditional IP packets – completely transparent to the end users.
38
RouterA is being used for mutual route redistribution between and EIGRP and OSPF networks. RouterB, one of RouterA’s EIGRP neighbors is missing a few routes in the OSPF domain. What should you check first?
A: Verify that RouterA, the border router, has the missing OSPF routes in its routing table.
The when troubleshooting missing redistributed routes between routing protocols, it is always a good practice to first verify that the router performing the redistribution shows the routes in its routing table.
If it does not, then you should inspect the routing protocol configuration hop-by-hop.
If the routes are in the border router’s routing table, inspect the redistribution configuration.
39
Which two dynamic routing protocols will continue to receive routing updates on an interface configured as passive?
A: RIP and RIPv2
The passive-interface command controls the advertisement of routing information differently depending on the routing protocol in use. With RIPv1 and RIPv2, the passive-interface command restricts outgoing advertisements only. EIGRP and OSPF drop their neighbor relationship and in doing so no longer send or receive advertisements on a passive interface.
RIP
The passive-interface command prevents the routing from sending multicast updates on the specified interface, but will still listen for incoming updates from RIP neighbors and keep their routes in the local routing table.
EIGRP/OSPF
Interfaces with the passive-interface command applied do not allow any routing updates or hellos out the interface. For EIGRP and OSPF, this means that the router will not form adjacencies with connected routers on that particular port. This essentially stops all outgoing and incoming updates since the neighbor relationship will drop.
40
If a BGP router has two paths to a destination and weight ans local preference attributes are not configured, what is the next attribute the router will consider to determine the best path?
What is the next-hop?
A: Local Origin
After weight and local preference, BGP considers the origin attribute to determine the best path. If the route originated locally, it will be preferred. A locally originated route will show a next-hop of 0.0.0.0 in the BGP table.
If it was not originated locally, the network with the shortest AS path is chosen. BGP uses the path selection criteria in the following order:
1. Highest weight
2. Highest local preference
3. Choose routes originated locally
4. Path with the shortest AS path
5. Lowest origin code ( i
41
Which of the following are not valid optional OSPF interface configuration parameters? What do each mean? What are their defaults?
```
database-interval
ip ospf dead-interval
ip ospf hello-interval
flood interval
ip ospf retransmit-interval
```
A: database-interval aand flood-interval are not optional OSPF interface configuration parameters
ip ospf dead-interval
Sets the interval at which hello packets must not be seen before neighbors declare the router down.
ip ospf hello-interval
Specifies the interval between hello packets sent on the interface.
ip ospf retransmit-interval
Specify the time between link-state advertisement (LSA) retransmissions for adjacencies belonging to the interface.
42
What is synchronization, and how does it influence BGP routes installed in the IP routing table?
A. If your AS passes traffic from another AS to a third AS, BGP should not advertise a route before all routers in your AS learn about the route via IGP. BGP waits until IGP propagates the route within the AS and then advertises it to external peers. A BGP router with synchronization enabled does not install iBGP learned routes into its routing table if it is not able to validate those routes in its IGP. Issue the no synchronization command under router bgp in order to disable synchronization. This prevents BGP from validating iBGP routes in IGP.
43
When issuing the show ip bgp command, you notice 0.0.0.0 as the next-hop for a network. What two ways could the network have been originated that would make 0.0.0.0 appear as the next-hop address?
A: The network was redistributed into BGP from an IGP or the network was originated from a aggregate or network command.
The fifth column shows the next hop address for each route. A 0.0.0.0 indicates the local router originated the route. This could include a network command entered locally or a network an IGP redistributed into BGP on the router.
Path is frequently ?.
44
Which routing protocol(s) require a metric to be assigned when redistributing routes from other routing protocols?
A: RIP, IGRP, and EIGRP require a metric to be assigned when redistributing routes into them
When you redistribute one protocol into another, remember that the metrics of each protocol play an important role in redistribution. Each protocol uses different metrics. For example, the Routing Information Protocol (RIP) metric is based on hop count, but Interior Gateway Routing Protocol (IGRP) and Enhanced Interior Gateway Routing Protocol (EIGRP) use a composite metric based on bandwidth, delay, reliability, load, and maximum transmission unit (MTU), where bandwidth and delay are the only parameters used by default.
RIP IGRP, and EIGRP all require a metric be manually configured for routes redistributed into them. In OSPF, if a metric is not specified, OSPF puts a default value of 20 when redistributing routes from all protocols except Border Gateway Protocol (BGP) routes, which get a metric of 1. For IS-IS, if no metric is specified, a metric value of 0 is used by default.
45
Which neighbors in the show ip bgp summary output have established a peering relationship with RouterA?
RouterA#show ip bgp summary
BGP currently operating:
AS: 100
Router ID: 10.10.10.10
Cluster ID: 33683901
Neighbor V AS MsgRcvd MsgSent Up/Down State/PfxRcd
1. 1.1.1 4 100 11 15 0:09:00 45
2. 2.2.2 4 200 27 28 0:23:03 Idle
3. 3.3.3 4 200 0 0 0:23:00 Idle
4. 4.4.4 4 200 0 0 0:00:27 Active
5. 5.5.5 4 300 0 0 0:16:49 31
In the show ip bgp summary output, established peers will show a number under the State/PfxRcd column referencing the number of prefixes received from the neighbor router. Depending on the IOS version, sometimes it will appear as “Estab”.
Idle indicates that the peer is not actively trying to peer. Active indicates that the router is actively trying to establish a peering relationship.
46
What is the default administrative distance for EIGRP external routes?
A: 170
The default administrative distance for EIGRP external routes in Cisco IOS is 170. The default administrative distance for EIGRP internal routes is 90.
```
Other default AD values:
RIP: 120
OSPF internal: 110
OSPF external: 110
iBGP: 200
eBGP: 20
Connected: 0
Static: 1
```
47
Based on the configuration below, how does the distribute-list effect communication with neighbor 10.10.10.2?
router bgp 65001
neighbor 10.10.10.2 remote-as 100
neighbor 10.10.10.2 distribute-list 110 in
!
access-list 110 permit ip 172.16.89.0 255.255.255.0 0.0.0.0
A: The local router will only allow route 172.16.89.0/24 from BGP neighbor 10.10.10.2
Distribute lists are access lists applied to the routing process, determining which networks are allowed into the routing table or included in updates. They essentially act as a filter.
In this case, the distribute-list is applied in the inbound direction to neighbor 10.10.10.2. The distribute-list filter references ACL 110, which permits the route 172.16.89.0/24 and denies all others.
router bgp 65001
neighbor 10.10.10.2 remote-as 100
neighbor 10.10.10.2 distribute-list 110 in
!
access-list 110 permit ip 172.16.89.0 255.255.255.0 0.0.0.0
48
What type of address does OSPFv3 use to establish neighbor adjacencies?
What is its address block?
A: OSPFv3 uses link-local addresses to establish neighbor adjacencies
fe80::/10
OSPFv3 is an updated version of OSPF designed to accommodate IPv6 natively. OSPFv3 uses the multicast address FF02::5 and FF02::6, but like EIGRP it uses its link-local address as the source address in advertisements.
49
RouterA is directly connected to two ISP routers (10.10.10.2 and 20.20.20.2) via BGP. Based on the configuration below, which ISP router will Router A use?
A: ISP router 10.10.10.2
On Cisco routers, weight is the most influential BGP attribute. The weight attribute is proprietary to Cisco and is normally used to select an exit interface when multiple paths lead to the same destination. Weight is local and is not sent to other routers. It can be a value between 0-65,535. 0 is the default.
We can see that the weight was set to 100 for neighbor 10.10.10.2, meaning RouterA will prefer that path. The weight to 20.20.20.2 would be the default of zero since none was explicitly configured.
50
What are the three techniques that can be used to transition from IPv4 to IPv6? Explain each.
A: Dual stack, tunneling, and NAT
Three options exist for transitioning from IPv4 to IPv6: dual stack, tunneling, or NAT.
Dual Stack – This involves running IPv4 alongside IPv6 on the same system.
Tunneling – This option allows you to encapsulate IPv6 traffic within an IPv4 header. An example is 6to4 tunneling.
NAT – A new network translation extension, NAT-PT allows IPv6-to4 translation.
51
True or False: BGP uses BGP hello and update messages to establish and maintain BGP neighbor relationships.
A: False
Unlike other dynamic routing protocols like EIGRP and OSPF, BGP neighbors must be manually configured using the neighbor command on both sides of the connection.
52
If your company using is using BGP in a multi-homed fashion to connect to two different ISPs, what should be done to prevent your AS from become a transit AS for one of the ISPs?
Can you give an example?
A: An outgoing distribution list or route map to filter all networks not originating from within your company’s BGP autonomous system.
Border Gateway Protocol (BGP) is one of the key protocols to use to achieve Internet connection redundancy. When you connect your network to two different Internet service providers (ISPs), it is called multi-homing. Multi-homing provides redundancy and network optimization.
When you are running BGP with more than one service provider, you run the risk that your autonomous system (AS) will become a transit AS. This causes Internet traffic to pass through your AS and potentially consume all of the bandwidth and resources on the CPU of your router.
A simple route-map filter example:
```
router bgp 100
network 10.10.10.0
network 20.20.20.0
neighbor 10.10.100.10 remote-as 100
neighbor 10.10.100.10 route-map internal out
neighbor 20.20.200.20 remote-as 200
neighbor 20.20.200.20 route-map internal out
!
route-map internal permit 10
match as-path 10
!
ip as-path access-list 10 permit ^$
```
53
What prefix does an edge router use when running 6to4 tunneling?
A: 2002::/16
6to4 tunnels use 2002::/16 IPv6 addresses in front of the 32 bit IPv4 address of the edge router – creating a 48 bit prefix. Each router on both sides of the tunnel needs a route to its peer. They only support static and BGP routes, so be careful.
Configure the tunnel as if it was a manual tunnel, using the IPv4 address as the source, but don’t enter a destination.The tunnel requires an IPv6 address using the method just described. Finally, use the command tunnel mode ipv6ip 6to4.
54
True or False:To configure OSPF MD5 authentication on a router, you must define a network key on an interface or enable authentication for the desired area.
A: False; to configure OSPF MD5 authentication, you must define a network key on an interface and enable authentication for the entire area.
Notice that the MD5 key is created using the interface-level command ip ospf message-digest-key 1 md5. Then authentucation is then enabled on the area under the OSPF router configuration mode using the area 0 authentication message-digest command. Pay close attention to the required statements as they look very similar.
RouterA#configure terminal
RouterA(config)#interface Serial0
RouterA(config-if)#ip ospf message-digest-key 1 md5 Strongp@ssword
RouterA(config-if)#exit
RouterA(config)#router ospf 1
RouterA(config-router)#area 0 authentication message-digest
RouterA(config-router)#end
55
What is the equivalent IPv4-mapped IPv6 address to IPv6 address ::ffff:A014:A014?
A: ::ffff:160.20.160.20
The point of this question tests your ability to convert HEX values to decimal for the IPv6 to IPv4 translation.
The first part of the IPv6 address can remain the same, so we will keep the ::ffff: prefix. Now we need to focus on the converting :A014:A014 from HEX to decimal. To do that we first break it into 4 separate blocks like this: A0 14 A0 14
Now we take each pair at a time and do the conversion. Starting with the left-most pair, A0, we can further separate it into individual digits: A 0
HEX numbers represent the following in decimal:
0=0, 1=1, 2=2, 3=3, etc. until we get to 9=9, 10=A, 11=B, 12=C, 13=D, 14=E, 15=F
So in this example, we have “A=10 0=0″. The right digit (0) stays the same. The left digit in the pair must be multiplied by 16 because that is how HEX numeration works. That means we now have: A=10*16=160 0=0
We can add the two decimal values together to arrive at our final number. 160+0=160. Time to go through the same process for the remaining three pairs of HEX quickly.
```
14 = 1 4 = 1*16 + 4 = 16 + 4 = 20
A0 = 10 0 = 10*16 + 0 = 160 + 0 = 160
14 = 1 4 = 1*16 + 4 = 16 + 4 = 20
```
Putting it all back together gives us:
::ffff:160.20.160.20
56
What are the default OSPF timer values
By default, OSPF uses a 10 second hello interval and 40 second hold timer on broadcast and point-to-point links and a 30 second hello interval and 120 second hold timer for all other network types.
57
What configuration level is manual EIGRP route summarization configured – router configuration mode or interface configuration mode?
Provide an example.
A: Interface configuration mode
EIGRP manual route summarization is configured on the interface level.
Example:
interface Serial0
ip address 10.10.10.1 255.255.255.0
ip summary-address eigrp 2000 172.16.10.0 255.255.255.0
58
After an IPv6 host boots, what type of IPv6 message does it send to determine the IP address of the local router?
A: A router solicitation message or RS
A Router Solicitation(RS) message can be sent by an IPv6 enabled host to receive information from a local router. If an IPv6 router receives the Solicitation message, it responds with a Router Advertisement (RA) which contains information about its routing table or perform stateless autoconfiguration. RAs are transmitted periodically, but a host may prompt for an immediate RA using a Router Solicitation such as when it boots or following a restart operation.
Router Advertisements contain the following characteristics:
+ Routers advertise periodically (between 4-1800 seconds)
+ RAs contain prefixes
+ Each prefix contains a lifetime
+ Specifies if stateful or stateless autoconfiguration is to be used
59
Fast convergence, partial routing updates, and VLSM support describes which routing protocol?
A: EIGRP
Enhanced Interior Gateway Routing Protocol, or EIGRP, is a Cisco proprietary, advanced distance vector dynamic routing protocol. Some benefits of EIGRP include:
Fast Convergence
EIGRP uses the DUAL algorithm to converge very quickly. It does this by knowing neighbor router’s routing tables and predefining primary and secondary routes to every destination network.
Triggered Updates
EIGRP uses partial triggered updates to its directly connected neighbors rather than periodically sharing its entire routing table. This saves link bandwidth because updates are only sent if a change is incurred, only the changes are sent in the update, and lastly – the updates are only sent to a routers’s affected neighbors. Very efficient!
Protocol Independent
Enhanced Interior Gateway Routing Protocol supports more than just IPv4. It supports IPv4, IPv6, IPX, and AppleTalk.
Multicast
EIGRP sends route updates, hellos, and queries to its neighbors using the multicast address 224.0.0.10 so end hosts are not affected. Hellos are sent out every 5 seconds by default to learn about new neighbors and make sure existing neighbors are still available.
VLSM Support
Variable length subnet masking is supported by EIGRP because it is a classless routing protocol. That means subnet masks are included in route updates.
60
After EIGRP automatically creates a summary route, what administrative distance is assigned to the summary route?
What does the route look like in the routing table?
A: 5
EIGRP supports two types of route summarization: automatic route summarization and manual route summarization. Automatic route summarization is enabled by default using the auto-summary command. This command allows EIGRP to perform automatic route summarization at classful boundaries.
In the router’s routing table, the summary route points to to the Null0 interface and has a default administrative distance value of 5. The router then advertises the summary route and suppresses the more specific routes.
61
Autonomous systems 65002 and 65003 have established eBGP sessions with their connected routers in AS 65001. An IGP has been configured on all routers in AS 65001 and they are successfully exchanging route information. Currently, packets from AS 65002 cannot reach AS 65003. What two changes need to be made on the routers in AS 65001 to enable the AS 65002 to 65003 traffic?
A: The BGP speakers in AS 65001 must be fully meshed and synchronization must be disabled on them.
62
Based on RouterA’s output below, which EIGRP neighbor is RouterA still waiting a query response from?
RouterA#show ip eigrp topology active
IP-EIGRP Topology Table for AS(1)/ID(10.10.10.2)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, r - Reply status
A 20.20.20.0/24, 1 successors, FD is 8541000, 1 replies, active 00:01:57, query-origin: Multiple Origins
via 10.1.1.1 (Infinity/Infinity), r, Serial0 serno 1243
via 10.1.2.1 (Infinity/Infinity), Serial1, serno 1567
The output in this scenario shows that RouterA has two neighbors to which it sent queries out for the 20.20.20.0/24 network. The (Infinity/Infinity) output tells is that this route is stuck-in-active since it it still waiting for at least one reply.
Notice the “, r,” in th output. That signifies that the local router has not received a query response from this router, which is 10.1.1.1.
via 10.1.1.1 (Infinity/Infinity), r, Serial0 serno 1243
via 10.1.2.1 (Infinity/Infinity), Serial1, serno 1567
63
RouterA is running OSPF and is an ABR between area 0 and area 2 with a distribute list applied. Assuming 10.20.3.0/29 is a valid, connected subnet in area 0, will RouterA create/send a Type 3 10.20.3.0/29 LSA into area 2?
RouterA(config)# router ospf 1
!
area 0 filter-list prefix AREA_0_OUT out
!
ip prefix-list AREA_0_OUT seq 5 deny 10.20.0.0/24 ge 26 le 30
ip prefix-list AREA_0_OUT seq 10 deny 10.10.0.0/16 ge 18 le 18
ip prefix-list AREA_0_OUT seq 20 permit 0.0.0.0/0 le 32
A: No
The example in this question shows an example of Type 3 LSA Filtering. The OSPF ABR Type 3 LSA Filtering feature extends the ability of an ABR that is running the OSPF protocol to filter type 3 link-state advertisements (LSAs) that are sent between different OSPF areas. This feature allows only packets with specified prefixes to be sent from one area to another area and restricts all packets with other prefixes. This type of area filtering can be applied out of a specific OSPF area, into a specific OSPF area, or into and out of the same OSPF areas at the same time.
10.20.3.0/29 matches the sequence number 5, denying the Type 3 LSAs from being sent out of area 0.
64
DMVPN and Virtual Tunnel Interface (VTI) are two VPN methods that use what protocol to provide secure connectivity between offices?
Describe the three types of tunnel.
A: IPSec
One major problem with standard IPSec sessions is that they do not support broadcast or multicast traffic. If you want to use an IPSec VPN in an “always on” fashion, then the tunnel needs to allow routing information to pass through. Of course dynamic routing protocols use broadcast or multicast to send hellos and updates, which creates a problem.
To get around this issue, a “tunnel within a tunnel” approach can be used. A generic tunnel can be configured within the IPSec tunnel to allow routing protocol information (along with all the other traffic). There are generally four ways to do this paired with IPSec:
DMVPN and GET VPN
Both allow the creation of secure, “on-demand”, multipoint tunnels.
Virtual Tunnel Interface (VTI)
A secure, “always-on” tunnel that supports multicast traffic. This allows routing protocols to operate within it.
Generic Routing Encapsulation (GRE)
GRE tunnels may be the most common of the bunch – they are also the default tunnel mode on Cisco routers. GRE tunnels support many layer 3 protocols but perhaps most importantly allow multicast traffic accross the tunnel – permitting dynamic routing protocol traffic. Be aware that GRE tunnels add an additional 20 byte IP header as well as a 4 byte GRE tunnel header.
65
Which two types of OSPF areas does an ABR inject a default route into?
A: Stub and Totally stubby areas
Both stub area and a totally stubby area allow an ABR to inject a default route, but there are two differences between the them.
A stub area replaces Type 5 LSAs (External LSAs – created by an ASBR to advertise network from another autonomous system) with a default route.
A totally stubby area replaces Type 5 LSAs and Type 3 LSAs (Summary LSA – created by an ABR to advertise network from other areas, but still within the AS, sometimes called inter-area routes) with a default route.
66
What is the order of OSPF states in which a router transitions to a full adjacency with an OSPF neighbor?
```
A: The order of OSPF states in which a router transitions to a full adjacency is:
1. Down
2. Init
3. 2-Way
4. Exstart
5. Exchange
6. Loading
7. Full
.
1. Down State
OSPF has not started and no hellos have been sent.
```
2. Init State
Hellos are sent out all OSPF-participating interfaces.
3. Two-way State
A hello is received from another router with its own RID in the neighbor field. All other required elements match and the routers become neighbors.
4. Exstart State
Routers determine which one will begin the route exchange process with the other.
5. Exchange State
Routers exchange DBDs.
67
Next-hop, exit interface, precedence are all attributes that can be manipulated using the set command. What is this type of routing path selection called?
A: Policy-based routing
Policy-based routing, or PBR, can change things like the exit interface, next-hop router, and QoS fields on traffic based on their source address.
To configure policy-based routing, you first create a route map. Next you must create match statements the route map will use to determine which source traffic to match. The last step is to define the set statements that change one or more of the attributes.
The set options include:
```
set ip precedence [number | name]
set ip df
set ip vrf vrf_name
set ip next-hop ip-address
set ip next-hop recursive ip-address
set interface interface-type interface-number
set ip default next-hop ip-address
set default interface interface-type interface-number
```
68
Which two dynamic routing protocols will continue to recieve routing updates on an interface configured as passive?
A: RIP and RIPv2
The passive-interface command controls the advertisement of routing information differently depending on the routing protocol in use. With RIPv1 and RIPv2, the passive-interface command restricts outgoing advertisements only. EIGRP and OSPF drop their neighbor relationship and in doing so no longer send or receive advertisements on a passive interface.
RIP
The passive-interface command prevents the routing from sending multicast updates on the specified interface, but will still listen for incoming updates from RIP neighbors and keep their routes in the local routing table.
69
When would a static route be used to form an adjacency between eBGP neighbors?
A: When the BGP routers do not have directly connected interfaces (as in the case of loopback interfaces).
When two eBGP peers need to establish neighbor relationship without using a direct physical connection between interfaces (ie. loopback interfaces), they must tell each other how to reach their interfaces. Static route provide a very simple solution to establish connectivity, especially when different ASs are used.
70
Which two design choices can help prevent CPU and memory resource issues in large OSPF networks?
A: Inter-area summarization and default routes to external destinations
If the OFSP domain is very large, breaking it up into several areas and manually summarizing contiguous routes between will reduce OSPF processing overhead.
When many external routes are injected into the OSPF domain, a better option is to use a default route out. That also reduces the size of the OSPF database and routing table.
71
What order does BGP use to evaluate (1-6)
1. Highest weight
2. Highest local preference
3. Choose routes originated locally
4. Path with the shortest AS path
5. Lowest origin code ( i < e < ? )
6. Lowest MED
7. eBGP route over iBGP route
8. Route with nearest IGP neighbor (lowest IGP metric)
9. Oldest route
10. Neighbor with the lowest router ID
11. Neighbor with the lowest IP address
72
Why would you use a point-to-multipoint non-broadcast network?
Is used in place of RFC-compliant point-to-multipoint mode if multicast and broadcast are not enabled on the virtual circuits, because the router cannot dynamically discover its neighboring routers using hello multicast packets
73
What are the default admin distances for the following?
```
RIP
OSPF internal
OSPF external
iBGP
eBGP
Connected: 0
Static: 1
```
```
RIP: 120
OSPF internal: 110
OSPF external: 110
iBGP: 200
eBGP: 20
Connected: 0
Static: 1
```
74
Why is it important for all routers in a transit iBGP AS to be fully meshed?
Does everything have to be physically connected?
A: Because routes learned from iBGP are never sent to other iBGP neighbors.
Two routers running BGP that form a TCP connection to exchange routing information are called BGP neighbors or peers. There must be IP connectivity between the two routers for the peer relationship to form.
The BGP split-horizon rule states that a route learned from one IBGP neighbor will not be advertised to another iBGP neighbor as a way to prevent routing loops from forming. For iBGP routers to learn about all BGP routes within the AS, all iBGP routers must be fully meshed. This is especially true for a transit AS. For eBGP routes to be propagated throughout the internal AS and then be advertised to other eBGP peers, full-mesh is required.
An import distinction is that fully meshed does not necessarily mean physically connected to every other device. As long as all iBGP routers can connect to all other BGP routers via TCP/IP, a logical fully-meshed topology can be created.
75
What are three methods to redistribute routes into EIGRP?
1. Use the redistribute command with the metric keyword.
2. Use the EIGRP default-metric router subcommand.
3. Use the redistribute command with a route-map to set the metrics.
All three methods are perfectly acceptable for of EIGRP route redistribution.
76
What is BGP's split horizon rule?
A route learned from one iBGP neighbor will not be advertised to another iBGP neighbor.
77
What metric are redistributed routes in OSPF given?
20 unless it is BGP which is assigned 1.
78
Under what circumstances are Type 2 LSAs generated ?
Type 2 LSAs are generated when a router running OSPF has an interface connected to a multi-access LAN segment (not point-to-point) and calls for the election of a Designated Router (DR) when at least two routers have been discovered. Keep in mind that Cisco IOS does not elect a DR on point-to-point links (or send Type 2 LSAS), but rather on LAN or multi-access connections with more than one OSPF router.
79
What protocol does OSPFv3 use to discover its neighbors?
What type of NDP messages are there?
Network Discover Protocol (NDP)
In IPv4 environments, ARP can be used to determine which hosts are on a segment. In IPv6, NDP is used and has enhanced features. NDP stands for Network Discovery Protocol. NDP actually uses ICMPv6 packets for the information exchange process. So while OSPFv3 routers do use NDP to discover and learn about each other, saying they use ICMP for neighbor discovery would also be true.
NDP uses uses 5 types of ICMPv6 packets:
- router solicitation
- router advertisement
- neighbor solicitation
- neighbor advertisement
- redirect message
80
How many links will OSPF perform equal-cost load balancing on by default?
Four
81
Based on RouterA’s configuration below, what is the effect of the distribute-list statement?
```
hostname RouterA
!
router eigrp 100
network 10.10.10.0 0.0.0.255
network 20.20.20.0 0.0.0.255
network 30.30.30.0 0.0.0.255
no auto-summary
distribute-list 1 in FastEthernet0/0
!
access-list 1 permit 40.40.40.0 0.0.0.255
```
RouterA will only allow 40.40.40.0/24 EIGRP route updates from RouterB on interface Fa0/0. The 30.30.30.0/24 routes will be filtered.
The command “distribute-list 1 in FastEthernet0/0″ defines a new distribute list for interface FastEthernet 0/0 that references access list 1. Access list 1 only permits the 40.40.40.0/24 network, meaning all other routes incoming on Fa0/0 will be dropped.
82
What possible conditions cause EIGRP Stuck-In-Active (SIA) routes?
Either EIGRP query or reply packets are lost between an EIGRP router and its neighbor or a unidirectional link failure has occured.
83
What is the correct IPv6 translation address of 192.168.85.1 when implementing a 6to4 tunnel?
2002:c0a8:5501::/48
This question requires two parts. First, you have to know that IPv6 addresses used by 6to4 tunnels always begin with “2002:”. The next step is to do the conversion from IPv4 decimal notation to IPv6 HEX notation.
For that we need to convert each octet individually and then combine them. 192 needs to be broken down into a 2-digit HEX value. The right-most HEX digit is represented by 16^0 and requires no change. The left-most HEX digit is represented by 16^1, meaning the decimal value must be divided by 16.
12*16=192, 12=C in HEX, 0=0 in HEX, 192+0=192, C0
10*16=160, 10=A in HEX, 8=8 in HEX, 160+8=168, A8
5*16=80, 5=5 in HEX, 5=5 in HEX, 80+5=85, 55
0*16=0, 0=0 in HEX, 1=1 in HEX, 0+1=1, 01
The last step is to add ::/48 to the end of the address. Putting it all together we have 2002:c0a8:5501::/48.
84
Do IPSec tunnels support an IGP?
No
85
Who wins the election for DR and BDR? Highest or lowest?
Highest.
86
Do GRE tunnels require loopback interfaces be configured? How do you configure a GRE tunnel?
No
GRE tunnels do not require that loopback interfaces be configured, but tunnel interfaces must be configured and in the same subnet. Configuring a GRE tunnel involves the following steps:
1. Create a tunnel interface
2. Adjust the TCP maximum transmission size and maximum segment size to prevent fragmentation due to the added GRE/IP headers (optional)
3. Define the tunnel source address (often a publicly routable IP address)
4. Define the tunnel destination address (often a publicly routable IP address)
5. Add a route to the remote network using the tunnel destination address as the next hop.
87
What EIGRP command prevents queries from being sent to a spoke router?
eigrp stub
The eigrp stub command can be applied to routers that represent the spoke in a hub-and-spoke network design. EIGRP stub routers usually only have a single neighbor, which can act as their default gateway.
Applying the eigrp stub command to the spoke router tells the hub router to not send EIGRP queries to the stub router. Because the stub router has no other connected routers, it will not be a useful source of alternate paths to a remote destination.
R1(config)#router eigrp 1
R1(config-router)# eigrp stub [receive-only | connected | static | summary | redistributed]
88
Which OSPF message contains all of the LSAs used during the database exchange process?
LSU
89
True or False: eBGP multipath is required when load-sharing over equal cost links from a single customer router to a single ISP router over eBGP.
A: False
eBGP multihop is required when load-sharing over equal cost links from a single customer router to a single ISP router over eBGP.
When a single BGP router has two equal-cost links to another BGP router in different a AS, link load balancing can be achieved by configuring eBGP multihop between the two routers. Additional requirements include using another routing protocol or static routes between the two routers.
eBGP multipath would be used to load balance links between a single BGP router and two ISP routers. That would involve the use of the maximum-paths keyword (similiar to the variance command in EIGRP).
90
RouterA is directly connected to RouterB and both are OSPF neighbors. RouterB’s OSPF configuration is shown below. RouterA is not receiving a default route from RouterB. What should be changed in the OSPF configuration on RouterB to resolve the issue?
```
hostname RouterB
!
interface fastethernet0/1
ip address 10.10.10.1 255.255.255.0
interface serial0/0
ip address 20.20.20.1 255.255.255.0
!
router ospf 1
network 10.10.10.0 0.255.255.255
network 20.20.20.0 0.255.255.255
default-information originate
```
Add the always keyword to the default-information originate command on RouterB
Default routes are injected into OSPF via type 5 LSAs. There are multiple ways to inject default routes into OSPF, but Cisco recommends using the default-information originate command under the OSPF routing process.
If the always keyword is not used, OSPF will only advertise a default route if the router it is configured on has a default route in its own routing table. If the always keyword is present, a default route will be advertised regardless if the route exists in the routing table.
In this case, since the default-information originate command is in place and RouterA is still not receiving the default router from RouterB, RouterB likely does not have its own default route. To force the 0.0.0.0 advertisement, the always keyword should be added.
router ospf 1
network 10.10.10.0 0.255.255.255
network 20.20.20.0 0.255.255.255
default-information originate always
91
You have connected via Ethernet and configured two routers to participate in EIGRP. You can successfully ping between two routers and have checked that the EIGRP network statements are correct, but are unable to get an EIGRP neighbor relationship to form. What should you check next?
The next step is to verify that there are no ACLs configured on the inbound interface of both routers.
When troubleshooting an EIGRP neighbor issue between two Cisco routers, the following steps should be performed:
1. Verify both routers are attached to the same primary network. EIGRP cannot use secondary IP addresses.
2. Verify that you can ping between the two devices.
3. Verify that EIGRP is enabled for the appropriate networks on both routers.
4. Verify that there are no ACLs configured on the inbound interface of both routers – so temporarily remove them.
5. Verify that the EIGRP hello interval and hold timers are configured to acceptable values.
92
True or False: In a multi-acces network, all OSPF routers send out network LSAs.
False
In a multi-acces network, only the DR router sends out network LSAs.
A DR, or designated router, only exists in a multi-access network and only the DR sends the Type 2 network LSAs using multicast address 224.0.0.5. The Non-Designated routers then use IP address 224.0.0.6 to communicate directly with the DR.
93
True or False:Using the show ip protocols command, you could indirectly determine the OSPF enabled and non-passive interfaces.
True
The show ip protocol command displays the parameters and current state of the active routing protocols, including OSPF.
If OSPF is configured using network commands, it will display the details of the configured network statements. However, if OSPF is configured using the interface-level ip ospf area command, it will list all of the interfaces enabled for OSPF. If any OSPF interfaces are in passive mode, those will be listed as well.
Using both outputs allow you to determine which interfaces are enabled for OSPF and active (All OSPF interfaces – passive interfaces = active and enabled).
94
Router A has been configured for mutual redistribution between EIGRP and OSPF as shown below. RouterA’s OSPF neighbor is receiving routes to the 10.20.10.0/24 network incorrectly. What should be changed in the configuration below to fix the redistribution?
```
router ospf 100
network 10.20.20.0 0.255.255.255 area 0
redistribute eigrp 50 metric 100
!
router eigrp 50
network 172.16.0.0 0.0.255.255
network 10.20.10.0 0.0.0.255
redistribute ospf 100
default-metric 10000 100 255 1 1500
```
The subnets keyword needs to be added to the redistribute command under router ospf 100.
router ospf 100
redistribute eigrp 50 metric 100 subnets
Without the subnets keyword added to the end of the redistribute command, OSPF will bring in the redistributed routes according to their classlfull boundaries. In this case, the 10.20.10.0/24 network would be redistributed into OSPF as 10.0.0.0/8. The subnets keyword allows the network to be redistributed as the actual source subnet.
95
When configuring 6to4 on a dual-stack router, the tunnel mode must be set to 6to4 and the IPv4 tunnel source must be configured. What is the last required step to complete the 6to4 tunnel configuration?
Configure a 6to4 IPv6 address (within 2002/16)
6to4 tunnels only require a few steps to complete a simple configuration. First, the tunnel itself must be defined (interface Tunnel0 below). Inside the tunnel configuration, the 6to4 IPv6 address must be set and begin with 2002:. Next, the tunnel source must be selected (interface Ethernet 0 in this example). Finally, the tunnel mode needs to be set to 6to4 via the “tunnel mode ipv6ip 6to4″ command.
Once the tunnel has been built, end-to-end routing can be performed using a simple static route using the tunnel interface as the net-hop.
```
interface Ethernet0
ip address 192.168.99.1 255.255.255.0
!
interface Tunnel0
ipv6 address 2002:c0a8:a010::1/64
tunnel source Ethernet 0
tunnel mode ipv6ip 6to4
!
ipv6 route 2002::/16 tunnel 0
```
96
True or False: Route tags use hop count as a unit of measure.
False
Route tags are unit-less integers that can be assigned to routes. The integer, like 55, that is assigned to the route can remain with the route regardless of the routing protocol in use of if redistribution occurs. As the name implies, route tags are simply a numbered tag. You can think of them as a admin-assigned label that is attached, independent of routing protocols or metrics.
97
When an IPv6 router running 6to4 tunneling needs to send a packet to a destination with a next hop address of 2002::/16, the IPv6 packet is first encapsulated inside an IPv4 packet using what IPv4 protocol type?
IPv4 protocol type 41
6to4 IPv6 packets are encapsulated into IPv4 using the type field value of 41 to let the receiving router know that the IPv4 packets contain an IPv6 6to4 tunnel payload.
98
What three items must be in place for route redistribution to work?
A router must have both routing protocols configured, have the redistribute command in place under each routing process, and at least one working link to the other router.
All three items must be in place for route redistribution to be successful. Understand that the redistribute command takes routing information the other routing protocols for its own use. For example, if you where to configure EIGRP and OSPF redistribution, when the redistribute command is used under the EIGRP process, OSPF routes are taken for use with EIGRP. In this example, OSPF is not “sending” routes to EIGRP, rather, OSPF is “pulling” to routes into itself.
99
What is required for a branch ISR router to configure an interface VLAN configuration?
A Cisco EtherSwitch Service Module
A Cisco EtherSwitch Service Module can be inserted into a Cisco ISR branch router to add layer2/3 switching capabilities. Doing so allows a branch router to be an all-in-one device that provides both routing and switching services for a small office. Once the EtherSwitch Service Module is installed, interface VLAN configurations (like access, trunk, etc.) can be applied to the module ports.
100
What is required for an OSPF neighborship to form?
```
OSPF requires the following for two routers to form a neighbor relationship:
+ Unique router IDs
+ Interfaces not passive
+ Matching hello timers
+ Matching dead timers
+ IPs in the same subnet and mask
```
The OSPF process ID is only locally significant to the router and does not effect neighbor relationships in any way.
101
In what container are Cisco IP SLA statistics stored for SNMP retrieval?
Cisco IP SLA statistics are stored using a specially created SNMP MIB named RTTMON-MIB.
Cisco IOS IP SLAs has a MIB called RTTMON-MIB. Each network performance statistical category spawns IP SLAs MIB variables and corresponding Object Identifiers (OIDs). Storing statistical results within an SNMP MIB allows a Network Monitoring Server, or NMS, to retrieve the IP SLA information remotely.
102
When developing an implementation plan for configuring EIGRP multipathing, what step should be performed before the configuration changes are made and immediately after?
A traffic baseline
When developing an implementation plan for configuring layer 3 multipath using EIGRP, a baseline should be captured before the work begins as well as after the configuration changes have been made. These steps will ensure that the multipath is in fact forwarding traffic in the way you expected and Cisco views it as an essential step in any multipath implementation plan.
103
Does Policy-Based Routing process packets inbound or outbound on an interface?
Inbound
Policy-Based Routing, or PBR only processes packets entering an interface, not outbound. PBR uses route maps to determine what traffic should be forwarded using the PBR policy. Traffic matching a permit clause in the route-map will be forwarded using the non-standard next hop. Traffic matching a deny clause will be routed normally.
104
What port does BGP use to send updates?
TCP port 179
A TCP connection between two BGP speakers is established before any routing information is exchanged using TCP port 179. BGP peers receive incremental, triggered updates as well as keepalives using the same port.
Also, BGP relies on TCP and its inherent retransmit controls to provide update reliability. There is no built-in BGP reliability mechanism for updates
105
What does the keyword default do for PBR?
If the default keyword is there it will attempt to forward using any nondefault routes first.
106
What is the correct syntax for adding two AS numbers to the AS path for AS 200?
route-map SETPATH permit 10 set as-path prepend 200 200
107
What are external routes inside an NSSA labeled as?
N1 or N2
108
What is PPP primarily used for?
CHAP authentication
109
Is there an OSPF hello/dead interval process on a virtual link?
No
110
In BGP what AS number range is reserved for private use
64,512-65,534
111
Does OSPF for ipv6 require that neighbors be in the same subnet?
No
112
Does OSPF prefer intra-area or inter-area routes?
Inter
113
What multicast address are router advertisements sent on?
FF02::1
114
What multicast address are router solicitations sent on?
FF02::2
115
What is the link local unicast address prefix for IPv6?
FF80::/10
116
What is the sit local unicast address?
FFC0::/10
117
What are the two static point to point tunnels?
GRE tunnels and manually configured tunnels
118
Does EIGRP encrypt all messages?
No
119
Will a tunnel still be up if the modes do not match?
Yes
120
For an ISATAP tunnel how would you convert an IPv4 address to IPv6 if the first 64 bits are given and the eui-64 command is given and a loopback interface exists.
The 5th and 6th octets become 0000:5EFE and the 7th and 8th octets would be the IPv4 address conversion.
121
Which BGP attributes are used in the path selection process if there is more than one route to the same destination within a single AS?
Weight and local preference
122
What is local preference used for?
Used within a multihomed AS and forces BGP routers to prefer one exit point over another when routing to a particular destination network.
123
What are the EIGRP packet types?
Hello - Establish neighbor relationships
Update - Send routing updates
Query - Ask neighbors about routing information
Reply - Respond to query about routing information
ACK - Acknowledge a reliable packet
