Dell EMC SmartFabric OS10 User Guide Release 10.5.0

Fast external fallover terminates EBGP sessions of any directly adjacent peer if the link used to reach the peer goes down. BGP does not wait for the hold-down timer to expire.

Fast external fallover is enabled by default. To disable or re-enable it, use the [no] fast-external-fallover command. For the fast-external-fallover command to take effect on an established BGP session, you must reset the session using the clear ip bgp {* | peer-ipv4-address | peer-ipv6-address} command.

View fast external fallover configuration

OS10(config)# do show running-configuration bgp
!
router bgp 300
 !
 neighbor 3.1.1.1
  remote-as 100
  no shutdown
 !
 neighbor 3::1
  remote-as 100
  no shutdown
  !
  address-family ipv6 unicast
   activate
OS10(config)# interface ethernet 1/1/1
OS10(conf-if-eth1/1/1)# show configuration
!
interface ethernet1/1/1
 ip address 3.1.1.3/24
 no switchport
 no shutdown
 ipv6 address 3::3/64
OS10(conf-if-eth1/1/1)# shutdown
OS10(conf-if-eth1/1/1)# do show ip bgp summary
BGP router identifier 11.11.11.11 local AS number 300
Neighbor                                      AS          MsgRcvd     MsgSent     Up/Down           State/Pfx
3.1.1.1                                       100         6           6           00:00:15          Active
3::1                                          100         8           11          00:00:15          Active
OS10(conf-if-eth1/1/1)#

View fast external fallover unconfiguration

OS10(config-router-bgp-300)# do show running-configuration bgp
!
router bgp 300
 no fast-external-fallover
 !
 neighbor 3.1.1.1
  remote-as 100
  no shutdown
 !
 neighbor 3::1
  remote-as 100
  no shutdown
  !
  address-family ipv6 unicast
   activate
OS10(config-router-bgp-300)#
OS10(conf-if-eth1/1/1)# do clear ip bgp *
OS10# show ip bgp summary
BGP router identifier 11.11.11.11 local AS number 300
Neighbor  AS          MsgRcvd     MsgSent     Up/Down     State/Pfx
-----------------------------------------------------------------
3.1.1.1   100         7           4           00:00:08    3
3::1      100         9           5           00:00:08    4
OS10#
OS10(config)# interface ethernet 1/1/1
OS10(conf-if-eth1/1/1)# shutdown
OS10(conf-if-eth1/1/1)# do show ip bgp summary
BGP router identifier 11.11.11.11 local AS number 300
Neighbor  AS          MsgRcvd     MsgSent     Up/Down     State/Pfx
-----------------------------------------------------------------
3.1.1.1   100         7           4           00:00:29    3
3::1      100         9           5           00:00:29    4
OS10(conf-if-eth1/1/1)#
OS10(config-router-bgp-neighbor-af)# Apr 27 01:39:03 OS10 dn_sm[2065]: Node.1-Unit.1:PRI:alert [os10:event],
 %Dell EMC (OS10) %BGP_NBR_BKWD_STATE_CHG: Backward state change occurred Hold Time expired for Nbr:3.1.1.3 VRF:default
 Apr 27 01:39:03 OS10 dn_sm[2065]: Node.1-Unit.1:PRI:alert [os10:event], %Dell EMC (OS10) %BGP_NBR_BKWD_STATE_CHG: Backward
 state change occurred Hold Time expired for Nbr:3::3 VRF:default