Route Refresh Capability

Two routes and one inbound policy

R1 advertises two host routes to R2. Begin with no inbound policy; both appear in R2’s accepted BGP table. This lab changes MED locally to make policy reprocessing visible.

hostname R1
ip cef
interface Loopback0
 ip address 10.255.0.1 255.255.255.255
exit
interface Loopback10
 ip address 198.51.100.1 255.255.255.255
exit
interface Loopback11
 ip address 198.51.100.2 255.255.255.255
exit
interface GigabitEthernet1
 ip address 192.0.2.1 255.255.255.252
 no shutdown
exit
router bgp 65001
 bgp router-id 10.255.0.1
 no bgp default ipv4-unicast
 neighbor 192.0.2.2 remote-as 65002
 address-family ipv4 unicast
  no auto-summary
  neighbor 192.0.2.2 activate
  network 198.51.100.1 mask 255.255.255.255
  network 198.51.100.2 mask 255.255.255.255
 exit-address-family
end

hostname R2
ip cef
interface Loopback0
 ip address 10.255.0.2 255.255.255.255
exit
interface GigabitEthernet1
 ip address 192.0.2.2 255.255.255.252
 no shutdown
exit
router bgp 65002
 bgp router-id 10.255.0.2
 no bgp default ipv4-unicast
 neighbor 192.0.2.1 remote-as 65001
 address-family ipv4 unicast
  no auto-summary
  neighbor 192.0.2.1 activate
 exit-address-family
end

R2# show ip bgp
     Network          Next Hop        Metric LocPrf Weight Path
*>   198.51.100.1/32  192.0.2.1            0             0 65001 i
*>   198.51.100.2/32  192.0.2.1            0             0 65001 i

Prepare the replay mechanism

R2# show ip bgp neighbors 192.0.2.1 | begin capabilities
Neighbor capabilities:
  Route refresh: advertised and received
  Address family IPv4 Unicast: advertised and received

Confirm that the peer can honor route refresh for this address family. The request is scoped to that family and neighbor, and the peer re-advertises its currently exportable routes. No extra pre-policy table is required solely for replay.

Change inbound MED

route-map IN-MED permit 10
 set metric 222
exit

router bgp 65002
 address-family ipv4 unicast
  neighbor 192.0.2.1 route-map IN-MED in
 exit-address-family

R2# clear ip bgp 192.0.2.1 soft in

R2# show ip bgp 198.51.100.1/32
BGP routing table entry for 198.51.100.1/32
  65001
    192.0.2.1 from 192.0.2.1
      Origin IGP, metric 222, localpref 100, valid, external, best

The changed attribute is visible after replay. TCP need not restart, but the resulting routing-policy change can still alter or remove forwarding paths; soft does not promise zero traffic impact.

Compare before-policy and after-policy information

Enhanced route refresh can bracket replay with beginning/end markers; support must be negotiated. A Route Refresh message is not an OPEN message and does not renegotiate the session’s original capabilities.

Remove the experiment and re-evaluate

router bgp 65002
 address-family ipv4 unicast
  no neighbor 192.0.2.1 route-map IN-MED in
 exit-address-family

R2# clear ip bgp 192.0.2.1 soft in

R2# show ip bgp 198.51.100.1/32
BGP routing table entry for 198.51.100.1/32
  65001
    192.0.2.1 from 192.0.2.1
      Origin IGP, metric 0, localpref 100, valid, external, best

If neither a stored copy nor negotiated refresh is available, a controlled hard reset may be necessary. Prefer a narrowly scoped operation with known consequences rather than clearing all peers.