Following my previous post with ebgp multihop, we have another way to establish eBGP peering when neighbor are peering using their loopbacks.
Establish the eBGP session between R10 and R6 using their loopbacks.
Configuration and verification:
I configure the peering between R10 and R6 using their loopback.
R10(config-router)#neighbor 10.100.1.6 remote-as 100 R10(config-router)#neighbor 10.100.1.6 update-source lo0 R6(config-router)#neighbor 10.10.1.10 remote-as 10 R6(config-router)#neighbor 10.10.1.10 update-source lo0
The eBGP session is not coming UP.
First, we have no connectivity between our loopbacks, we will need to add a static route because the loopback are not seen as directly connected.
R10#PING 10.100.1.6 SO lo0 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 10.100.1.6, timeout is 2 seconds: Packet sent with a source address of 10.10.1.10 ..... Success rate is 0 percent (0/5) R10(config)#ip route 10.100.1.6 255.255.255.255 eth0/0 R6(config)#ip route 10.10.1.10 255.255.255.255 Ethernet0/1
Now the eBGP session is still not up.
Remember that by default the TTL for eBGP is set to one, because we are peering with the loopback we need to change that otherwisw the peering will not be establish.
We could have used the ebgp multihop command but when the two routers are directly connected, it is better to use the disable connected check command.
R10(config-router)#neighbor 10.100.1.6 disable-connected-check R6(config-router)#neighbor 10.10.1.10 disable-connected-check
Now the BGP session is UP.
*Jul 7 20:35:00.053: %BGP-5-ADJCHANGE: neighbor 10.100.1.6 Up R10#sh ip bgp neigh 10.100.1.6 BGP neighbor is 10.100.1.6, remote AS 100, external link BGP version 4, remote router ID 10.100.1.6 BGP state = Established, up for 00:02:25 Last read 00:00:35, last write 00:00:35, hold time is 180, keepalive interval is 60 seconds Neighbor sessions: 1 active, is not multisession capable (disabled) SNIP Connection state is ESTAB, I/O status: 1, unread input bytes: 0 Connection is ECN Disabled, Mininum incoming TTL 0, Outgoing TTL 1
As you can see the outgoing TTL is still set to 1.
Coming next, more BGP option for peering.
Thank you for reading.
BGP – implement and troubleshoot Peerings – Neighbor Disable-Connected-Check