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6 - IPv4 Routing Flashcards

1
Q

What is a CSU/DSU?

A

Channel service unit/Data service unit

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2
Q

What is an SFP port?

A

Small Form Pluggable port. Allows you to choose a an SFP that supports the type of cabling provided by the Ethernet WAN provider opposed to the other standard RJ-45 port that supports copper cabling (implied for LAN)

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3
Q

What is a notable difference between Cisco Routers and Switches with regards to power?

A

Switches typically do not have an on/off switch

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4
Q

What two features are SOHO Routers likely to have that Enterprise routers typically are less likely to have?

A
  1. SOHO routers almost always use Internet and VPN technology for their WAN connections to send data back and forth to rest of the Enterprise
  2. SOHO routers typically use a multi-function device that does routing, LAN switching, VPN, wireless, etc
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5
Q

Do Cisco switches have Aux ports?

A

No

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6
Q

What is the difference in default settings for Telnet and SSH between Routers and Switches?

A

Routers default to disallow Telnet and SSH

Switches allow Telnet and SSH by default

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7
Q

What devices support the show mac address-table command?

A

Switches. Routers do not.

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8
Q

What is the difference between show interfaces status on a Switch and Router?

A

On a switch the command lists one line of output per interface. But on a Router a different command must be used (show ip interface brief)

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9
Q

What is the difference between the show interfaces status command and show ip interface brief command?

A

The first command is used on a Switch while the second lists similar information on routers

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10
Q

What does each status code mean for an interface status? e.g. up/up

A

Line Status/Protocol Status

  • Line Status refers to whether Layer 1 is working
  • Protocol Status is mainly Data Link protocol (L2)
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11
Q

What could it mean if the Line Status is down?

A

Cable issues, devices not powered on

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12
Q

What could it mean if the Protocol Status is down?

A

Mismatched data-link layer configuration e.g. PPP vs HDLC, or could be down if the Line Status is down

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13
Q

What does it mean if the line status is Administratively down?

A

The interface has a shutdown command configured on it

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14
Q

What kind of information does the show protocols command show?

A

State of the router interfaces (Line Status/Protocol Status)

IP address and mask

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15
Q

What do Aux ports do?

A

Works like a console port. But typically connected through a cable to external analog modem, which in turn connects to a phone line

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16
Q

What command do you use to configure the Aux port?

A

line aux 0

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17
Q

What two things does a router consider when receiving a data link frame?

A
  1. If it has no Frame errors (FCS field)

2. Frames destination data link address is the router’s address or appropriate multicast/broadcast address

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18
Q

Why do routes for remote subnets typically list both an outgoing interface and next-hop router IP address?

A

Because routes for subnets that connect directly to the router do not need to be sent to another router so they can list only an outgoing interface

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19
Q

What is a connected route?

A

A route added because of the configuration of a the ip address command

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20
Q

What is a static route?

A

A route added because of the use of the ip route global command

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21
Q

What is a local route?

A

Host route - A route that defines a route for just that one IP (has /32 prefix). Used for the routers interface on that subnet.

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22
Q

What two facts must be true for the router to automatically add a route to its routing table for the subnet connected to each interface?

A
  1. Interface is in a working state (up/up)

2. Interface has IP address assigned through ip address command

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23
Q

What is the routing protocol code for OSPF?

A

O

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24
Q

What is the Prefix another name for?

A

Subnet ID

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25
What does the router use its ARP table for?
Transmitting packets to hosts connected to the same subnet as the router
26
What is the default timeout for an ARP entry on Cisco IOS?
240 minutes
27
How do you show the ARP table on a router?
show ip arp
28
What command is used to configure static routes?
ip route
29
When is a static route considered a 'network route'?
When the destination specified defines a subnet, or entire Class A, B or C network
30
What is a default route?
A route that matches all destination IPs e.g. 0.0.0.0
31
What is a host route?
A route that matches a single IP address
32
How do you show only static routes from the routing table?
show ip route static
33
Why should you always use the next hop IP for routes that will send packets out an Ethernet interface?
Because using the next hop IP identifies the specific device in the connected subnet
34
How does a router pick a route if there are two routes that match?
It uses the one with the longest prefix length
35
What is a floating static route?
A route that floats / moves in and out of the routing table depending on whether the better (lower) administrative distance route learned by the routing protocol exists currently. Router ignores static route during times when better routing protocol is known
36
What must a router do when a static route competes with other static routes / routes learned by protocols?
Decide which one is the most specific (prefix) or has the better administrative distance
37
True/False: By default IOS considers OSPF better than static routes?
False
38
What is the default administrative distance for OSPF learned routes?
110
39
What is the default administrative distance for static routes?
1
40
How do you set a floating static route?
ip route destination_ip mask next-hop administrative_distance
41
How would you show the administrative distance for a given route?
show ip route 172.16.2.0
42
What are two reasons a static route might not appear in the routing table after being configured (with either outgoing interface or next hop IP)?
1. The outgoing interface is not in an up/up state | 2. The local router does not have a route to reach the next hop address
43
How can you configure a static route so that basic checks are ignored and it is permanent?
Adding the 'permanent' keyword to ip route commands
44
What is the routing metric and administrative distance for the following route? 10.2.2.0/30 [110/128] via 10.2.2.5, 14:31:52, Serial0/0/1
Administrative distance 110 | Route metric 128
45
True/False: Show ip route output of the routing table is organized by classful network?
True
46
What is the time in a routing table output?
Time since route was first learned (OSPF and EIGRP)
47
What is the routing protocol code for EIGRP?
D
48
What is ROAS?
A feature where a router interface can connect to multiple VLAN based subnets using a single interface, and route traffic between them. It achieves this using sub-interfaces (multiple virtual router interfaces)
49
Do Cisco routers typically attempt to negotiate trunking?
No
50
How would you configure trunking on a Router?
interface Ge0/0.10 encapsulation dot1q 10 ip address 10.1.1.1 255.255.255.0
51
True/False: The subinterface numbers have to match the VLAN ID when configuring ROAS
False
52
What are the two options for configuring native VLANs on the trunk for ROAS?
1. Configure on the normal physical interface, with NO encapsulation command 2. Configure the IP on the sub-interface and use the `encapsulation dot1q 10 native` command
53
What two commands are best to verify ROAS configuration?
1. show ip route [connected] | 2. show vlans
54
What kind of site would it make sense to use a ROAS at?
Small remote sites
55
What are the two main options for enabling IPv4 routing on a switch?
1. SVI | 2. Routed interfaces
56
What is a SVI?
Switched Virtual Interface.
57
What does L3 Switching function require to be connected to each VLAN?
A virtual interface
58
How do you enable IP routing on Switches that require it to be manually enabled?
sdm prefer lanbase-routing reload ip routing
59
How do you configure an SVI on a switch?
interface vlan 10 ip address 10.1.1.1 255.255.255.0 no shutdown
60
What commands would you use to verify SVIs?
show ip route | show ip int brief
61
What are the two main things you need to investigate when troubleshooting SVIs?
1. Has IP routing been enabled on the switch? | 2. Check VLAN associated with each interface is known and active on local switch. Else VLAN interfaces won't come up
62
What are the requirements for interfaces when expecting an SVI to work?
The switch must have at least one up/up interface that is assigned to that VLAN or a trunk interface for which the VLAN is in the allowed list (and is STP forwarding and not VTP pruned)
63
How do routed interfaces / routed ports on switches work?
Make a physical port act like a router interface
64
What is the key difference between a normal switch port and a routed port?
The routed port does not perform Layer 2 switching, instead triggering L3 routing logic when a frame arrives on that port
65
What is the key difference between L2 and L3 EtherChannels with respect to how they treat the channel?
L3 EtherChannels treat the channel as a Routed port, instead of a switched port
66
When would you use a routed interface / routed port with respect to connections to subnets?
When an L3 Switch needs an L3 interface connected to the subnet, and only ONE physical interface connects to that subnet
67
When would you use a SVI with respect to connections to subnets?
When an L3 Switch needs a L3 interface connected to a subnet and MANY physical interfaces on the switch connect to that subnet
68
How do you make a switch interface a routed interface?
Use the `no switchport` command
69
Where would a routed interface show up in the output of `show interfaces status`
Under the VLAN heading with the word routed
70
Where should you use Routed interfaces?
Any topologies with a Point to Point link between two devices that do routing
71
Where should you use SVIs?
VLANs for which many interfaces (access and trunk) connect to the VLAN. Because SVIs can send and receive traffic out multiple ports on the same switch
72
What is a downside of configuring routed ports for multiple links between switches and then enabling a routing protocol?
Multiple routes will be learned with the same neighboring switch as the next hop
73
What is L3 EtherChannel?
Where multiple links act as one Layer 3 link
74
How would you configure an L3 EtherChannel?
``` Each interface: channel-group 10 mode on no switchport (make routed port) Port Channel interface: interface port-channel 10 no switchport ip address ```
75
Does the channel-group number have to be the same for neighboring switches?
No. Only for the interfaces on the switch in that channel
76
True/False: when configuring the EtherChannel the IP should not be placed on the PortChannel interface
False. It should only be placed on the PortChannel interface
77
How do you show details about a port channels interfaces?
show interfaces port-channel 10
78
What commands are useful for verifying the port channel?
show etherchannel summary show interfaces status show interfaces port-channel
79
What are the two main areas to consider when troubleshooting an L3 EtherChannel?
1. Channel group configuration (interface for etherchannel) | 2. Check the list of settings that must match on the interfaces for an L3 EtherChannel to work
80
What are the requirements that must match for an interface to be in an L3 EtherChannel?
1. Speed 2. Duplex 3. Configured using `no switchport`

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