What does configuring an EIGRP stub do, and what does the default stub advertise?
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A stub router announces in its hellos that it is a stub. Its neighbors then stop sending it queries,
and it stops acting as a transit path: it only advertises the route types you allow. Plain
eigrp stub means connected summary. Other options are static, redistributed, receive-only, and a
leak-map to let chosen learned routes through. The classic use is branch and spoke routers, so a
failure at the hub never sends queries to hundreds of branches.
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Configuring it
Classic mode:
router eigrp 100
eigrp stub connected summaryNamed mode:
router eigrp BRANCH
address-family ipv4 unicast autonomous-system 100
eigrp stub connected summaryThe options
| Keyword | Advertises |
|---|---|
| connected | Connected subnets covered by network statements or redistributed |
| summary | Summaries configured on this router |
| static | Redistributed static routes |
| redistributed | All redistributed routes |
| receive-only | Nothing |
| leak-map | Learned EIGRP routes matched by a route map, on top of the other choices |
Verifying from the hub
HUB1# show ip eigrp neighbors detail | include Stub|Suppressing
Stub Peer Advertising (CONNECTED SUMMARY ) Routes
Suppressing queriesWhy transit matters
A branch dual-homed to HUB1 and HUB2 learns the data center from both. Without stub, it advertises those routes back to the other hub, and the hubs can end up using a small branch link as a path to each other when their own link fails. Stub stops that.
They will ask next
What do you need on the hub if a branch is receive-only?
Static routes to the branch LAN, usually redistributed into EIGRP. A receive-only stub advertises nothing, so the network never learns its subnets.
Does a stub router still send queries itself?
Yes. Stub only stops other routers from querying it. If its own path to something fails, it can go active and query its neighbors like any router.
Traps
- Confusing it with an OSPF stub area. EIGRP stub controls what the router advertises and whether it gets queries, not what it receives.