General routing protocol troubleshooting:
• interface down or [network] not enabled for a routing protocol
• passive interface
• misconfigured authentication
• access-lists (denying routing protocol packets)
• route filtering (a route not advertised or learned)
RIP troubleshooting:
• wrong version: the sender and receiver must use the same version for RIP updates
• max hop count exceeded: 16 hops is unreachable
• autosummarization: summarizes classless networks to classful boundaries; problematic in discontiguous networks
EIGRP troubleshooting:
• [primary] IP addresses in different subnets (see link)
• mismatched AS numbers
• mismatched K values
• unique router IDs (when injecting external routes into EIGRP)
• NOTE: timers do not have to match
• see: Fundamental EIGRP Concepts
OSPF troubleshooting:
• mismatched timers
• mismatched area numbers
• mismatched area types
• mismatched network types
• MTU mismatch
• duplicate router IDs
• different subnets
• OSPF configured on secondary subnet but not on primary
• see: OSPF Neighbor Problems Explained
BGP troubleshooting:
• broken Layer 3 connectivity (must reach [remote] IP)
• incorrect neighbor statement (wrong peer address or remote AS)
• path to peer is via default route
• wrong source IP (update-source)
• TTL expires (eBGP vs iBGP)
• see: Troubleshooting BGP
Why BGP routes might be missing from the BGP table or the routing table:
•bad or no ’network <> mask <>’ command (must be exact)
•next-hop unreachable
•BGP ”split horizon” (iBGP route not advertised to another iBGP peer)
•better source (lower AD)
•route filtering
The BGP ‘network <> mask <>’ command:
• the network/prefix to be advertised in BGP must be in the routing table from some other source
• must be a perfect match in the routing table
• if these requirements are not met, the network/prefix will not be advertised
Redistribution:
•route must be in the routing table
•routing protocols use different metrics, so a conversion needs to happen —> seed metric
•default seed metric for RIP and EIGPR is unreachable
•default OSPF seed metric is 20 (1 for BGP)
A seed metric can be defined in three ways (listed in order of preference):
1️⃣ a route-map configuration applied to the ’redistribute’ command
2️⃣ the ’metric’ parameter in the ’redistribute’ command
3️⃣ the ’default-metric’ command
• interface down or [network] not enabled for a routing protocol
• passive interface
• misconfigured authentication
• access-lists (denying routing protocol packets)
• route filtering (a route not advertised or learned)
RIP troubleshooting:
• wrong version: the sender and receiver must use the same version for RIP updates
• max hop count exceeded: 16 hops is unreachable
• autosummarization: summarizes classless networks to classful boundaries; problematic in discontiguous networks
EIGRP troubleshooting:
• [primary] IP addresses in different subnets (see link)
• mismatched AS numbers
• mismatched K values
• unique router IDs (when injecting external routes into EIGRP)
• NOTE: timers do not have to match
• see: Fundamental EIGRP Concepts
OSPF troubleshooting:
• mismatched timers
• mismatched area numbers
• mismatched area types
• mismatched network types
• MTU mismatch
• duplicate router IDs
• different subnets
• OSPF configured on secondary subnet but not on primary
• see: OSPF Neighbor Problems Explained
BGP troubleshooting:
• broken Layer 3 connectivity (must reach [remote] IP)
• incorrect neighbor statement (wrong peer address or remote AS)
• path to peer is via default route
• wrong source IP (update-source)
• TTL expires (eBGP vs iBGP)
• see: Troubleshooting BGP
Why BGP routes might be missing from the BGP table or the routing table:
•bad or no ’network <> mask <>’ command (must be exact)
•next-hop unreachable
•BGP ”split horizon” (iBGP route not advertised to another iBGP peer)
•better source (lower AD)
•route filtering
The BGP ‘network <> mask <>’ command:
• the network/prefix to be advertised in BGP must be in the routing table from some other source
• must be a perfect match in the routing table
• if these requirements are not met, the network/prefix will not be advertised
Redistribution:
•route must be in the routing table
•routing protocols use different metrics, so a conversion needs to happen —> seed metric
•default seed metric for RIP and EIGPR is unreachable
•default OSPF seed metric is 20 (1 for BGP)
A seed metric can be defined in three ways (listed in order of preference):
1️⃣ a route-map configuration applied to the ’redistribute’ command
2️⃣ the ’metric’ parameter in the ’redistribute’ command
3️⃣ the ’default-metric’ command
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