Wednesday 5 May 2021

To verify layer 3 reachability, use the ping command.

To view EIGRP peers/neighbors and the interfaces that they are reachable through;

#show ip eigrp topology

#debug eigrp packets <terse>

watch out for stub configurations, passive interfaces, K-value mismatches summarization (IPv4, IPv6)

EIGRP issues are usually;

Neighbor Issues

Are interfaces operational
Does EIGRP AS match
Are interfaces enabled for EIGRP
Is there an interface that is configured as passive?
Authentication
Interface is down: The interface must be up/up.
Mismatched autonomous system numbers: Both routers need to be using the same autonomous system number.
Incorrect network statement: The network statement must identify the IP address of the interface you want to include in the EIGRP process.
Mismatched K values: Both routers must be using exactly the same K values.
Passive interface: The passive interface feature suppresses the sending and receiving of hello packets while still allowing the interface’s network to be advertised.
Different subnets: The exchange of hello packets must be done on the same subnet; if it isn’t, the hello packets are ignored.
Authentication: If authentication is being used, the key ID and key string must match, and the key must be valid (if valid times have been configured).
ACLs: An access control list (ACL) may be denying packets to the EIGRP multicast address 224.0.0.10.
Timers: Timers do not have to match; however, if they are not configured correctly, neighbor adjacencies could flap.

Verification of Neighbor Issues

#show ip eigrp neighbors <detail>

To identify whether the physical and data-link layers are operational;

#show ip interface brief

#show ip eigrp interface <detail>

AS: the AS specified in the router command
Interface: the interfaces over which EIGRP is configured
Peers: number of directly connected EIGRP neighbors on the interface
Xmit: Queue Unreliable and Reliable: The number of packets remaining in the unreliable and reliable queues
Mean SRTT: the average Smooth Round Trip Time (SRTT) interval in milliseconds, for all neighbors on the interface.
Pacing Time Unreliable and Reliable: number of milliseconds to wait after transmitting unreliable and reliable packets.
Multicast Flow Timers: number of milliseconds to wait for an acknowledgement of a multicast packet by all the neighbors before transmitting the next multicast packet.
Pending Routes: number of routes in the packets in the transmit queue that are waiting to be sent.

#show ip protocols

Are networks being advertised?
Is ACL blocking advertisements?
Is there a discontiguous network issue?
Redistribution
Summarization
Bad or missing network command: The network command enables the EIGRP process on an interface and injects the prefix of the network the interface is part of into the EIGRP process.
Better source of information: If exactly the same network prefix is learned from a more reliable source, it is used instead of the EIGRP learned information.
Route filtering: A filter might be preventing a network prefix from being advertised or learned.
Stub configuration: If the wrong setting is chosen during the stub router configuration, or if the wrong router is chosen as the stub router, it might prevent a network prefix from being advertised.
Interface is shut down: The EIGRP-enabled interface must be up/up for the network associated with the interface to be advertised.
Split horizon: Split horizon is a loop-prevention feature that prevents a router from advertising routes out the same interface on which they were learned.

#show ip interface brief

#show ip route eigrp

#show ip protocols

#show access-list

#show ip protocols

#show ip eigrp neighbor detail

Discontiguous Subnets

Poorly summarized supernets; show ip route

Summarization requires at least one subnet in the RIB for summary to be advertised.