11 - Troubleshooting Routing Protocols

Question 1

What 4 conditions do both EIGRP and OSPF require be met to establish a neighbor relationship?

Answer 1

• Interfaces must be in an up/up state * Interfaces must be in the same subnet * ACLs must not filter routing protocol messages * Must pass authentication if configured

Question 2

What additional conditions does EIGRP require be met to establish a neighbor relationship?

Answer 2

• Must use the same ASN * K-values must match

Question 3

What additional conditions does OSPF require be met to establish a neighbor relationship?

Answer 3

• Hold and Dead timers must match * Router_IDs must be unique * The neighbor interfaces must be in the same area

Question 4

If an exam question appears to be related to a problem with a routing protocol, what 3 general troubleshooting processes are described in this book for both EIGRP and OSPF?

Answer 4

Step 1.) looking at the design determine which interfaces should have routing protocols enabled and which routers should become neighbors. Step 2.) Verify whether a routing protocol is enabled on each interface. Step 3.) Verify that each router has formed all expected neighbor relationships.

Question 5

For both EIGRP and OSPF what 2 things does the routing protocol do once enabled on an interface using the ‘network’ cmd?

Answer 5

• Attempts to find potential neighbors on the subnet connected to that interface * Advertise the subnet connected to that interface

Question 6

For both EIGRP and OSPF, if a routing protocol is enabled on an interface but a neighbor relationship does not form, what could be the problem?

Answer 6

• Passive interface could be configured on that interface.

Question 7

For EIGRP interfaces, what 2 commands are all that are needed to determine 1) if the routing protocol is enabled and 2) which interfaces are configured to be passive?

Answer 7

• ‘show ip eigrp interfaces’ and ‘show ip protocols’

Question 8

For OSPF interfaces, what 2 commands are all that are needed to determine 1) if the routing protocol is enabled and 2) which interfaces are configured to be passive?

Answer 8

• show ip ospf brief * show ip protocols

Question 9

What information is contained in the ‘show ip protocols’ command?

Answer 9

• the contents of the configured network commands for each routing protocol * a separate list of the passive interfaces.

Question 10

What information is contained in the ‘show ip eigrp interfaces’ command?

Answer 10

• all EIGRP-enabled interfaces * Does NOT show passive-interfaces

Question 11

What information is contained in the ‘show ip ospf interface brief’ command?

Answer 11

• lists all OSPF-enabled interfaces * DOES include passive-interfaces

Question 12

For OSPF, what does the ‘show ip protocols’ command show?

Answer 12

• lists all OSPF-enabled interfaces * DOES include passive-interfaces

Question 13

In EIGRP, what are the two formats acceptable for the ‘network’ command?

Answer 13

• network 10.0.0.0 - must be a classful network, will include all interfaces in that classful network or * use a wildcard mask ‘network 10.2.0.0 0.0.255.255

Question 14

What does the command ‘show ip eigrp neighbors’ show?

Answer 14

Only EIGRP neighbors that have passed the neighbor verification checks.

Question 15

In EIGRP, if the ‘show ip eigrp neighbors’ cmd does not show all the expected neighbors what is the first thing to check?

Answer 15

Can the neighbors ping each other on the same subnet. You have to specify the source interface of the ping.

Question 16

In EIGRP, while checking for a specific neighbor that doesn’t show up, and pings work, what is the next step?

Answer 16

Go down the list of verification requirements.

Question 17

In EIGRP, what kind of authentication is used for neighbor relationships (if configured)?

Answer 17

MD5

Question 18

In EIGRP, what show command displays the K values?

Answer 18

show ip protocols’

Question 19

In EIGRP, which 2 show commands displays the ASN number?

Answer 19

show ip eigrp neighbors’ and ‘show ip protocols’

Question 20

In OSPF, what command lists all the OSPF routers that have met all the requirements for being neighbors?

Answer 20

show ip ospf neighbors

Question 21

in OSPF, on a shared link such as Ethernet which two states would you expect to find?

Answer 21

full’ for neighbor relationships with DR and BDR and ‘2-way’ for relationships between DROthers

Question 22

In OSPF, if the ‘show ip ospf neighbors’ cmd does not show all the expected neighbors what is the first thing to check?

Answer 22

Can the neighbors ping each other on the same subnet. You have to specify the source interface of the ping.

Question 23

In OSPF, while checking for a specific neighbor that doesn’t show up, and pings work, what is the next step?

Answer 23

Go down the list of verification requirements.

Question 24

In OSPF, what debug command would show two potential neighbors not on the same subnet?

Answer 24

debug ip ospf hello

Question 25

In OSPF, what debug command would you use to show whether the two potential neighbors were using the same Hello and Dead timers?

Answer 25

debug ip ospf hello

Question 26

In OSPF, what debug command would show if the two potential neighbors were in the same Area?

Answer 26

debug ip ospf adjacency

Question 27

In OSPF, what two places would you look to see if the RIDs were unique?

Answer 27

show ip ospf’ and the log messages

Question 28

In OSPF, what debug command would show you if two routers were having issues becoming neighbors

Answer 28

debug ip ospf adjacency

Question 29

In OSPF, which command takes precedence, the ‘network’ command under ‘router ospf’ or the ‘ip ospf’ interface command?

Answer 29

The ip ospf interface command.