Which routing protocol settings does DMVPN need with EIGRP, OSPF and BGP?
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EIGRP: in phase 2, turn off split horizon and next-hop-self on the hub tunnel so spokes learn each
other's prefixes with the remote spoke as next hop; in phase 3, summarize from the hub instead. Make
spokes EIGRP stubs. OSPF: the default point-to-point network type on tunnels allows one neighbor, so
use broadcast with spokes at priority 0 in phase 2, or point-to-multipoint in phase 3. BGP: dynamic
neighbors on the hub with bgp listen range, iBGP with the hub as route reflector or eBGP with a
private AS per spoke, and in phase 3 just a summary or default to the spokes.
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EIGRP on the hub
! Phase 2
interface Tunnel0
no ip split-horizon eigrp 100
no ip next-hop-self eigrp 100
! Phase 3
interface Tunnel0
ip summary-address eigrp 100 10.0.0.0 255.0.0.0Spokes: eigrp stub connected under router eigrp 100.
OSPF
- Point-to-point (the tunnel default) accepts one neighbor, so a hub with several spokes flaps.
- Broadcast (hello 10, dead 40) keeps the next hop, needs the hub as DR.
- Point-to-multipoint (hello 30, dead 120) sets the hub as next hop, fine for phase 3.
- All spokes share one area, so every spoke flap triggers SPF on every spoke. This limits scale.
BGP on the hub
router bgp 65000
neighbor SPOKES peer-group
neighbor SPOKES remote-as 65000
bgp listen range 172.16.0.0/24 peer-group SPOKES
address-family ipv4
neighbor SPOKES activate
neighbor SPOKES route-reflector-clientA route reflector does not change the next hop by default, which is what phase 2 needs.
They will ask next
Why make spokes EIGRP stubs?
When the hub loses a route it would otherwise query every spoke, and one slow spoke can cause stuck in active. Stubs are not queried. Stubs also do not re-advertise learned routes, so a dual-hub spoke never becomes a transit path between hubs.
The hub and spokes run different OSPF network types. What happens?
Broadcast and point-to-multipoint use different hello and dead timers by default (10/40 vs 30/120), so hellos do not match and no adjacency forms. Set the same type on every tunnel interface.
Traps
- Summarizing on the hub in a phase 2 design. Spoke-to-spoke tunnels stop forming.