EIGRP Commands Cheat Sheet
Quick reference for classic (and named-mode) EIGRP on Cisco IOS: enable an autonomous system, advertise interfaces, tune metrics/timers, secure adjacencies, and verify neighbors and topology. All commands are real IOS syntax with <placeholders> for your values.
Part of the EIGRP learning hub
1. Enable EIGRP
The wildcard on network is an inverse mask; enable EIGRP per interface whose IP falls in that range.
| Command | What it does |
|---|---|
router eigrp <asn> | Enter EIGRP config for autonomous system <asn> (1-65535); must match on all neighbors. |
network <ip-address> <wildcard-mask> | Advertise/enable EIGRP on interfaces whose IP matches; e.g. network 10.1.1.0 0.0.0.255. |
network <ip-address> | Classful form (no wildcard) — enables EIGRP on all interfaces in that major network. |
eigrp router-id <a.b.c.d> | Manually set the 32-bit router-ID (else highest loopback, then highest active IP). |
no auto-summary | Disable automatic summarization at classful boundaries — required for discontiguous subnets. |
passive-interface <interface> | Stop sending/receiving hellos out <interface> (no adjacency), but still advertise its subnet. |
passive-interface default | Make all interfaces passive; re-enable with 'no passive-interface <interface>'. |
2. Metrics & timers
bandwidth/delay are interface commands feeding the metric (delay is in TENS of microseconds); variance/maximum-paths are under 'router eigrp'.
| Command | What it does |
|---|---|
bandwidth <kbps> | Interface: sets bandwidth used in the metric (does not change actual line rate). |
delay <tens-of-microseconds> | Interface: sets delay used in the metric; value is in tens of microseconds. |
ip hello-interval eigrp <asn> <seconds> | Interface: hello timer for that AS (5s LAN / 60s low-speed NBMA default). |
ip hold-time eigrp <asn> <seconds> | Interface: dead timer for that AS; need not match a neighbor's, but should exceed its own hello. |
variance <multiplier> | Router: enable unequal-cost load balancing (1-128); includes feasible successors up to multiplier x FD. |
maximum-paths <number> | Router: max parallel routes installed (default 4; up to 16/32 by platform). |
3. Summarization & authentication
Manual summary is per-interface; MD5 auth uses a key chain referenced on the interface.
| Command | What it does |
|---|---|
ip summary-address eigrp <asn> <network> <mask> | Interface: advertise a manual summary out this interface (creates a Null0 discard route). |
key chain <name> | Global: create a key chain to hold authentication keys. |
key <key-id> | Key-chain: define a key by number. |
key-string <password> | Key: set the shared secret string for this key. |
ip authentication mode eigrp <asn> md5 | Interface: enable MD5 authentication for that AS. |
ip authentication key-chain eigrp <asn> <key-chain-name> | Interface: bind the key chain used to authenticate for that AS. |
4. Named-mode EIGRP (brief)
Modern config under one 'router eigrp <name>'; per-AS settings live in an address-family, interface settings under af-interface.
| Command | What it does |
|---|---|
router eigrp <name> | Enter named-mode (the <name> is a local process tag, not the AS number). |
address-family ipv4 unicast autonomous-system <asn> | Define the AS; contains network, router-id, af-interface, and topology sub-modes. |
network <ip-address> <wildcard-mask> | Under the address-family: advertise/enable matching interfaces (same as classic). |
af-interface <interface> | Per-interface tuning (hello-interval, hold-time, summary-address, authentication, passive-interface); use 'af-interface default' for all. |
topology base | Under the address-family: where 'variance' and 'maximum-paths' are set in named mode. |
5. Verification
Neighbors first, then topology (successors/FS), then the routing table.
| Command | What it does |
|---|---|
show ip eigrp neighbors | Adjacencies: neighbor IP, local interface, hold time, uptime, SRTT — confirms peering. |
show ip eigrp topology | Successors and feasible successors with FD/RD; add 'all-links' to see non-FS routes. |
show ip route eigrp | EIGRP-learned routes in the RIB (internal D = AD 90, external D EX = AD 170). |
show ip protocols | AS number, K-values, router-ID, networks, passive interfaces, variance, maximum-paths. |
show ip eigrp interfaces | Interfaces running EIGRP, peer count, and pacing; add 'detail' for hello/hold and auth. |
Frequently asked questions
Why do I need 'no auto-summary' in EIGRP?
By default classic EIGRP summarizes routes to their classful boundary when advertising across a major-network boundary. With discontiguous subnets (e.g. 10.1.1.0 and 10.1.2.0 separated by a 172.16.x link) auto-summary makes both routers advertise 10.0.0.0/8, causing missing or flapping routes. 'no auto-summary' sends the specific subnets so routing works. Named-mode EIGRP has auto-summary off by default.
My EIGRP neighbors won't form — what should I check?
Adjacency requires: the same autonomous-system number, matching K-values (metric weights), interfaces on the same primary subnet, and matching authentication (mode plus a valid key-string). Also confirm the interface isn't 'passive-interface' and isn't administratively down. Hello/hold timers do NOT have to match to form a neighborship. Use 'show ip eigrp neighbors', 'show ip protocols', and 'debug eigrp packets' to pinpoint the mismatch.
How does 'variance' enable unequal-cost load balancing?
Variance multiplies the successor's feasible distance; any route whose metric is within that multiple is eligible to be installed. Crucially, only feasible successors qualify — a path is used only if it already satisfies the feasibility condition (its reported distance is less than the successor's FD), which guarantees a loop-free path. Routes that fail feasibility are never used no matter how high you set variance.
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