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CCNP ENCOR > Ch 6: IP Routing Essentials > Flashcards

Ch 6: IP Routing Essentials Flashcards

1
Q

Which of the following routing protocols is classified as an EGP?

a. RIP
b. EIGRP
c. OSPF
d. IS-IS
e. BGP

A

E. BGP is the only Exterior Gateway Protocol listed here.

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2
Q

Which of the following routing protocols are classified as IGPs? (Choose all that apply.)

a. RIP
b. EIGRP
c. OSPF
d. IS-IS
e. BGP

A

A, B, C, and D. RIP, EIGRP, OSPF, and IS-IS are all classified as Interior Gateway Protocols.

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3
Q

A path vector routing protocol finds the best loop-free path by using ______.

  1. hop count
  2. bandwidth
  3. delay
  4. interface cost
  5. path attributes
A
  1. BGP is a path vector routing protocol that selects the best path based on path attributes such as MED, local preference, and AS_PATH length.
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4
Q

A distance vector routing protocol finds the best loop-free path by using ______.

  1. hop count
  2. bandwidth
  3. delay
  4. interface cost
  5. path attributes
A
  1. Distance vector protocols, such as RIP, only use hop count to select the best path.
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5
Q

A link-state routing protocol finds the best loop free path by using ______.

  1. hop count
  2. bandwidth
  3. delay
  4. interface cost
  5. path attributes
A
  1. Link-state routing protocols use the interface cost as the metric for Shortest Path First (SPF) calculations.
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6
Q

A router uses _________ as the first criterion for forwarding packets.

  1. path metric
  2. administrative distance
  3. longest match
  4. hop count
A
  1. The Cisco CEF sorts all network prefixes from shortest match to longest match for programming of the FIB. The path with the longest match is more explicit than a generic path.
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7
Q

A router uses _________ as the second criterion for forwarding packets.

  1. path metric
  2. administrative distance
  3. longest match
  4. hop count
A
  1. When two different routing protocols attempt to install the same route into the RIB, the route with the lowest AD is installed into the RIB.
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8
Q

The ability to install multiple paths from the same routing protocol with the same path metric into the RIB is known as ______.

  1. per-packet load balancing
  2. round-robin load balancing
  3. equal-cost multipathing
  4. parallel link forwarding
A
  1. Equal-cost multipath is the installation of multiple paths (that are deemed the best path) into the RIB when they come from the same routing protocol.
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9
Q

Which static route should be used to avoid unintentional forwarding paths with an Ethernet link failure?

  1. A directly attached static route
  2. A recursive static route
  3. A fully specified static route
  4. A static null route
A
  1. Ethernet links should not use a directly attached static route, and a link failure could result in the resolution of the next-hop IP address resolving to an unintentional link. The fully specified static route ensures that the next hop is resolvable using only the specified interface.
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10
Q

Virtual routing and forwarding (VRF) is useful with _____ addresses.

  1. MAC
  2. IPv4
  3. IPv6
  4. IPv4 and IPv6
A
  1. VRFs support multiprotocol (IPv4 and IPv6) addressing.
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11
Q

T/F: BGP can function as both an IGP and and EGP

A

BGP is an EGP protocol but can also be used within an autonomous system. If BGP exchanges routes within an autonomous system, it is known as an interior BGP (iBGP) session. If it exchanges routes between different autonomous systems, it is known as an exterior BGP (eBGP) session.

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12
Q

T/F: A distance vector protocol selects paths purely based on distance

A

T: A distance vector protocol selects paths purely based on distance. It does not account for link speeds or other factors.

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13
Q

Which of the following is not correct about EIGRP?

  • It offers rapid convergence time for changes in the network topology.
  • It sends periodic full routing table updates like DV protocols
  • It uses hellos and forms neighbor relationships just as link-state protocols do.
  • It uses bandwidth, delay, reliability, load, and maximum transmission unit (MTU) size instead of hop count for path calculations.
  • It has the option to load balance traffic across equal- or unequal-cost paths.
A

The diffusing update algorithm (DUAL) is an enhanced distance vector algorithm that EIGRP uses to calculate the shortest path to a destination within a network. EIGRP advertises network information to its neighbors as other distance vector protocols do, but it has some enhancements, as its name suggests. The following are some of the enhancements introduced into this algorithm compared to other distance vector algorithms:

  • It offers rapid convergence time for changes in the network topology.
  • It sends updates only when there is a change in the network. It does not send full routing table updates in a periodic fashion, as distance vector protocols do.
  • It uses hellos and forms neighbor relationships just as link-state protocols do.
  • It uses bandwidth, delay, reliability, load, and maximum transmission unit (MTU) size instead of hop count for path calculations.
  • It has the option to load balance traffic across equal- or unequal-cost paths.
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14
Q

T/F: A link-state dynamic IP routing protocol advertises the link state and link metric for each of its connected links only to every directly connected neighbor router in it’s AS.

A

False.

A link-state dynamic IP routing protocol advertises the link state and link metric for each of its connected links and directly connected routers to every router in the network.

OSPF advertisements are called link-state advertisements (LSAs), and IS-IS uses link-state packets (LSPs) for its advertisements.

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15
Q

What is the LSDB?

A

As a router receives an advertisement from a neighbor, it stores the information in a local database called the link-state database (LSDB) and advertises the link-state information on to each of its neighbor routers exactly as it was received.

The link-state information is essentially flooded throughout the network, unchanged, from router to router, just as the originating router advertised it. This allows all the routers in the network to have a synchronized and identical map of the network.

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16
Q

What is the Dijkstra algorithm?

A

Using the complete map of the network, every router in the network then runs the Dijkstra shortest path first (SPF) algorithm to calculate the best shortest loop-free paths. The link-state algorithm then populates the routing table with this information.

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17
Q

T/F: In addition to using less memory and CPU, distance vector protocols are less prone to routing loops than link state protocols.

A

Due to having the complete map of the network, link-state protocols usually require more CPU and memory than distance vector protocols, but they are less prone to routing loops and make better path decisions.

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18
Q

T/F: A router identifies the path a packet should take by evaluating the prefix length that is programmed in the Forwarding Information Base (FIB).

A

True.

A router identifies the path a packet should take by evaluating the prefix length that is programmed in the Forwarding Information Base (FIB). The FIB is programmed through the routing table, which is also known as the Routing Information Base (RIB). The RIB is composed of routes presented from the routing protocol processes. Path selection has three main components:

  1. Prefix length: The prefix length represents the number of leading binary bits in the subnet mask that are in the on position.
  2. Administrative distance: Administrative distance (AD) is a rating of the trustworthiness of a routing information source. If a router learns about a route to a destination from more than one routing protocol, and all the routes have the same prefix length, then the AD is compared.
  3. Metrics: A metric is a unit of measure used by a routing protocol in the best-path calculation. The metrics vary from one routing protocol to another.
19
Q

What are the ADs for the following routed protocols or connection types? hint: These are in the right order.

  • Connected
  • Static
  • EIGRP summary route
  • External BGP (eBGP)
  • EIGRP (internal)
  • OSPF
  • IS-IS
  • RIP
  • EIGRP (external)
  • Internal BGP (iBGP)
A

As each routing protocol receives routing updates and other routing information, it chooses the best path to any given destination and attempts to install this path into the routing table. Table 6-3 provides the default ADs for a variety of routing protocols.

20
Q

When a route is to be added to the RIB, what must be true for the two cases that the route is added?

A

The RIB is programmed from the various routing protocol processes. Every routing protocol presents the same information to the RIB for insertion: the destination network, the next-hop IP address, the AD, and metric values. The RIB accepts or rejects a route based on the following logic:

  1. If the route does not exist in the RIB, the route is accepted.
  2. If the route exists in the RIB, the AD must be compared. If the AD of the route already in the RIB is lower than the process submitting the second route, the route is rejected. Then that routing process is notified.
  3. If the route exists in the RIB, the AD must be compared. If the AD of the route already in the RIB is higher than the routing process submitting the alternate entry, the route is accepted, and the current source protocol is notified of the removal of the entry from the RIB.
21
Q

T/F: Changing the AD can cause routing loops.

A

True.

The default AD might not always be suitable for a network; for instance, there might be a requirement to adjust it so that OSPF routes are preferred over EIGRP routes. However, changing the AD on routing protocols can have severe consequences, such as routing loops and other odd behavior, in a network. It is recommended that the AD be changed only with extreme caution and only after what needs to be accomplished has been thoroughly thought out.

22
Q

What is ECMP? T/F: RIP, EIGRP, OSPF, BGP and IS-IS all support ECMP.

A

Equal-Cost Multipathing

If a routing protocol identifies multiple paths as a best path and supports multiple path entries, the router installs the maximum number of paths allowed per destination. This is known as equal-cost multipathing (ECMP) and provides load sharing across all links. RIP, EIGRP, OSPF, and IS-IS all support ECMP. ECMP provides a mechanism to increase band- width across multiple paths by splitting traffic equally across the links.

23
Q

T/F: The command sh ip route displays the FIB.

A

False. This will display the RIB, Routing Information Base.

RIB - Routing information base - sh ip route ( shows rib- Where routing table is built- CONTROL PLANE)

FIB - Forward Information base - sh ip cef (this is where RIB looks when deciding where to forward the traffic - DATA PLANE)

24
Q

T/F: By default, routing protocols install only routes with the lowest path metric.

25
T/F: EIGRP has UCLB, Unequal Cost Load Balancing, enabled by default.
False. However, EIGRP can be configured (not enabled by default) to install multiple routes with different path metrics. This allows for unequal-cost load balancing across multiple paths. Traffic is transmitted out the router’s interfaces based on that path’s metrics in ratio to other the interface’s metrics.
26
Static routes are useful when ■ Dynamic routing protocols cannot be used on a router because of limited router CPU or memory ■ Routes learned from dynamic routing protocols need to be superseded But, what are two downsides to using static routes?
If a link goes down, other routers will not be aware that the network path is no longer valid. i.e. There is no network intelligence. Administrative overhead for engineers. Scalability issues.
27
What is a directly attached static route?
Point-to-point (P2P) serial interfaces do not have to worry about maintaining an adjacency table and do not use Address Resolution Protocol (ARP), so static routes can directly reference the outbound interface of a router. **A static route that uses only the outbound next-hop interface is known as a directly attached static route,** and it requires that the outbound interface be in an up state for the route to be installed into the RIB. Directly attached static routes are configured with the command **ip route** *network subnet-mask next-hop-interface-id.* **NOTE**: Configuring a directly attached static route to an interface that uses ARP (that is, Ethernet) causes problems and is not recommended. The router must repeat the ARP process for every destination that matches the static route, which consumes CPU and memory. Depending on the size of the prefix of the static route and the number of lookups, the con- figuration can cause system instability.
28
What does a directly connected route show as the AD/Metric with the command **sh ip route?**
A directly attached static route does not display [AD/Metric] information when looking at the routing table. Notice that the static route displays directly connected with the outbound interface.
29
What is a recursive static route?
**A recursive static route specifies the IP address of the next-hop address.** The recursive lookup occurs when the router queries the RIB to locate the route toward the next-hop IP address (connected, static, or dynamic) and then cross-references the adjacency table. Recursive static routes are configured with the command **ip route** *network subnet-mask next-hop-ip.* Recursive static routes **require the route’s next-hop address to exist** in the routing table to install the static route into the RIB. A recursive static route may not resolve the next-hop forwarding address using the default route (0.0.0.0/0) entry. The static route will fail next-hop reachability requirements and will not be inserted into the RIB.
30
What is the AD/Metric of a recursive static route that shows with the command **sh ip route?**
[1/0]
31
T/F: Static route recursion can simplify topologies if a link fails because it may allow the static route to stay installed while it changes to a different outbound interface in the same direction as the destination.
True. This adds resiliency but also introduces a possible problem. The problems arise if the recursive lookup resolves to a **different interface pointed in the opposite direction.** To correct this issue, the static route configuration should use the outbound interface and the next-hop IP address. A static route with both an interface and a next-hop IP address is known as a *fully specified static route.*
32
What is a fully specified static route?
A static route with both an interface and a next-hop IP address is known as a fully specified static route. If the interface listed is not in an up state, the router removes the static route from the RIB. Specifying the next-hop address along with the physical interface removes the recursive lookup and does not involve the ARP processing problems that occur when using only the outbound interface. Fully specified static routes are configured with the command **ip route** *network subnet-mask interface-id next-hop-ip*.
33
T/F: The default AD on a static route is 1, but a static route can be configured with an AD value of 1 to 256 for a specific route.
False. Close... The default AD on a static route is 1, but a static route can be configured with an AD value of 1 to **255** for a specific route.
34
What is a floating static route and how is it configured?
The default AD on a static route is 1, but a static route can be configured with an AD value of 1 to 255 for a specific route. The AD is set on a static route by appending the AD as part of the command structure. Using a floating static route is a common technique for providing backup connectivity for prefixes learned via dynamic routing protocols. A floating static route is configured with an AD higher than that of the primary route. Because the AD is higher than that of the primary route, it is installed in the RIB only when the primary route is withdrawn. The floating route will not be in the RIB unless the route with a better metric disappears.
35
What is a static null route and why would you use one?
The null interface is a virtual interface that is always in an up state. Null interfaces do not forward or receive network traffic and drop all traffic destined toward them without adding overhead to a router’s CPU. Configuring a static route to a null interface provides a method of dropping network traffic without requiring the configuration of an access list. Creating a static route to the Null0 interface is a common technique to prevent routing loops. The static route to the Null0 interface uses a summarized network range, and routes that are more specific point toward the actual destination.
36
What is the command to create an ipv6 static route? What must be globally enabled first for this to work?
The static routing principles for IPv4 routes are exactly the same for IPv6. It is important to ensure that IPv6 routing is enabled by using the global configuration command **ipv6 unicast routing**. IPv6 static routes are configured with the command **ipv6 route** *network/ prefix-length { next-hop-interface-id | [next-hop-interface-id] next-ip-address}.*
37
T/F: When creating an ipv6 static route, if the next-hop address is an IPv6 link-local address, the static route must be a fully specified static route.
True.
38
What is VRF?
Virtual routing and forwarding (VRF) is a technology that creates separate virtual routers on a physical router. The following characteristics are true: * Router interfaces, routing tables, and forwarding tables are completely isolated between VRFs, preventing traffic from one VRF from forwarding into another VRF. * All router interfaces belong to the global VRF until they are specifically assigned to a user defined VRF. * The global VRF is identical to the regular routing table of non-VRF routers.
39
T/F: With VRFs it is possible to have overlapping IP address ranges in your route tables.
Every router’s VRF maintains a separate routing table; therefore it is possible to allow for overlapping IP address ranges. VRF creates segmentation between network interfaces, network subinterfaces, IP addresses, **and** routing tables. Configuring VRF on a router ensures that the paths are isolated, network security is increased, and encrypting traffic on the network is not needed to maintain privacy between VRF instances.
40
What commands are necessary to create a multi-protocol VRF instance on a router?
1. The creation of multiprotocol VRF instances requires the global configuration command **vrf definition** *vrf-name.* 2. Under the VRF definition submode, the command **address-family** *{ipv4 | ipv6}* is required to specify the appropriate address family. 3. The VRF instance is then associated to the interface with the command **vrf forwarding** *vrf-name* under the interface configuration submode.
41
What is the command to view the RIB with VRFs?
**show ip route vrf** *vrf-name.* Example 6-22 shows how the VRF configured IP addresses and routes do not appear in the global routing table. The global route table is unaware of VRFs,
42
T/F: VRFs are analogous to VLANs.
True, but at L3 instead of L2. VRF instances on a router can be compared to that of virtual local area networks (VLANs) on a switch. However, instead of relying on Layer 2 technologies such as spanning tree, VRF instances allow for interaction and segmenation with Layer 3 dynamic routing protocols. Using routing protocols over Layer 2 technologies has some advantages, such as improved network convergence times, dynamic traffic load sharing, and troubleshooting tools such as ping and traceroute.
43
What are the commands to configure a... 1. directly attached static route 2. recursive static route 3. fully specified static route
**directly attached:** * **ip route** *network subnet-mask next-hop-interface-id* **recursive:** * **ip route** *network subnet-mask next-hop-ip* **f****ully specified:** * **ip route** *network subnet-mask interface-id next-hop-ip*

CCNP ENCOR (30 decks)

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