- Static route
- Policy-based routing (PBR)
- VRF
- Summarization
- IP route profile
Static route
- if next-hop = bcast interface, then next-hop – directly connected (sends ARP)
- CEF updates ARP entry immediately on route creation
- if there is no ARP reply, route is still used (incomplete ≡ drop)
- if both next-hop and interface are specified, next-hop must be reachable via interface for entry to be valid
- permanent:
- remains in RIB after next-hop gets unreachable
- next-hop must reply to ARP/NDP for entry to be initially created
(config)# ip route [<INTF>] <NEXTHOP> [permanent]
; 60s default, CPU intensive, interval for next-hop reachability check for static routes
(config)# ip route static adjust-time <sec>
Policy-based routing (PBR)
- override routing logic, ingress packets only
- requires corresponding SDM template for CEF
- CPU intensive on older HW
- set interface
- IPv4 P2P only
- IPv4 multi-access is awkward
- IPv6 supported only if there is a route in RIB
(config-route-map)# match ip address <ACL>
; packet length
(config-route-map)# match length <MIN> <MAX>
; egress interface according to RIB
(config-route-map)# match interface <INTF>
; IP has to be connected, first address via up/up interface is used
(config-route-map)# set ip next-hop <IP1> <IP2> ...
; first – route with RIB, if match on 0.0.0.0/0 – run PBR
(config-route-map)# set ip default next-hop <IP1> <IP2> ...
; P2P interface, sends ARP for next-hop, if reachable via another interface – magic
(config-route-map)# set interface <INTF>
; P2P interface, sends ARP for destination, drops proxy ARP because of sanity check
(config-route-map)# set default interface <INTF>
; for locally generated packets
(config)# ip local policy route-map <MAP>
(config-if)# ip policy route-map <MAP>
; interfaces with PBR and corresponding route-map
# show ip policy
VRF
- by default endpoint for tunnel are searched in global RIB
- NAT
- VRF → global
- VRF → VRF (same)
- global →× VRF: PBR is required to switch RIB
; change global VRF for NAME in route search for tunnel endpoint
(config-if)# tunnel vrf <NAME>
Summarization
- reduce impact of subordinate route flapping
- accelerate restoration after failure
- cost (IGP) or attributes (BGP) should be set manually to avoid subordinate route change to cause summary update
IP route profile
- tracks number of RIB changes during 5s
- can detect control plane churn: counter increase for higher counts
(config)# ip route profile
# show ip route profile