Troubleshooting EIGRP Route Advertisement and Missing Routes
Neighbors up but a route is missing? A systematic walk through the five places an EIGRP route can die on its way to the routing table, with real failure output from a CML lab.
EIGRP
Enhanced Interior Gateway Routing Protocol, Cisco's hybrid distance-vector IGP. Articles tagged EIGRP cover the DUAL algorithm, composite metric and K values, stub routing, adjacency requirements, and Cisco IOS XE configuration.
Latest posts — page 2
Troubleshooting EIGRP Neighbor Adjacencies: The Loud Failure and the Silent One
Two routers, two broken adjacencies, one log message. Real CML captures on IOS XE 17.18.2 show the %DUAL-5-NBRCHANGE K-value mismatch that repeats every few seconds, the AS mismatch that logs absolutely nothing, and what both look like the moment they recover.
EIGRP Route Filtering with Distribute Lists and Route Maps
Filter EIGRP routes with distribute lists powered by prefix lists and route maps. Both flavors configured on a live CML lab, with before-and-after routing tables and the habits that keep filtering from becoming a mystery outage.
EIGRP Wide Metrics: 64-Bit Metrics in Named Mode
Named mode EIGRP replaced the 32-bit composite metric with a 64-bit version: delay in picoseconds, a scaling factor before the routing table, and quiet conversions at classic/named boundaries. Decoded with real CML output.
EIGRP Query Process and Stuck-in-Active (SIA) Explained with Real Captures
A route in Active state with a reply outstanding, captured live on IOS XE 17.18.2 in CML: the r and rs status flags that name the silent neighbor, why packet loss gives you neighbor flaps instead of SIA, and why modern IOS XE usually logs retry limit exceeded before it ever prints %DUAL-3-SIA.
EIGRP Authentication: MD5 and SHA in Classic and Named Mode
Unauthenticated EIGRP forms adjacencies with anything that speaks the protocol. This post configures MD5 key chains and HMAC-SHA-256 in classic and named mode on a live CML lab, then breaks a key to show what failure looks like.
EIGRP Unequal-Cost Load Balancing: Variance Explained
EIGRP is the only Cisco IGP that load balances across unequal-cost paths. This lab walks variance on live IOS XE: the topology table, the feasibility check, variance 2 in named mode, and the traffic share counters that prove the split.
EIGRP Route Summarization and Default Routes
EIGRP summarization shrinks topology tables, speeds convergence, and bounds queries. Configure it in classic and named mode on IOS XE, watch the Null0 discard route appear, and advertise a default route with summary-address 0.0.0.0/0.
EIGRP Administrative Distance: 90, 170, and 5
EIGRP has three administrative distances, not one: 90 internal, 170 external, 5 for summaries. Each value encodes a deliberate trust decision. This post explains why they differ and how to read and change them.
EIGRP Neighbor Requirements: The 5 Things That Must Match
The 5 things that must match for EIGRP routers to become neighbors: subnet, AS number, K-values, authentication, and process membership. Plus what does NOT need to match.
Routing Protocols Over GRE: OSPF, EIGRP, BGP
Run OSPF, EIGRP, and BGP across GRE tunnels on Cisco IOS XE. Recursive routing fix, OSPF network types, EIGRP metric tuning, and BGP update-source.
EIGRP Stub Routing for Hub-and-Spoke
EIGRP stub routing makes hub-and-spoke topologies scale. The five stub options, query suppression, DMVPN integration, and the production patterns for branch deployments.