What does hop count signify in EBGP multihop

[Neil227]

Consider the above scenario. I configured ebgp neighborship to form between R1 and R4.

Below mentioned are the device configs:

R1(config-router)#do sh ip int br
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 unassigned YES NVRAM administratively down down
Serial0/0 40.1.1.1 YES NVRAM up up
FastEthernet0/1 unassigned YES NVRAM administratively down down
Serial0/1 20.1.1.2 YES NVRAM up down
Serial0/2 unassigned YES NVRAM administratively down down
Serial0/3 unassigned YES NVRAM administratively down down

R1#

router bgp 200
no synchronization
bgp log-neighbor-changes
network 20.1.1.0 mask 255.255.255.0
network 40.1.1.0 mask 255.255.255.0
neighbor 20.1.1.1 remote-as 100
neighbor 40.1.1.2 remote-as 200
neighbor 60.1.1.1 remote-as 400
neighbor 60.1.1.1 ebgp-multihop 255 <<<<
no auto-summary

R4#

router bgp 400
no synchronization
bgp log-neighbor-changes
network 60.1.1.0 mask 255.255.255.0
neighbor 40.1.1.1 remote-as 200
neighbor 40.1.1.1 ebgp-multihop 255<<<<<<<<<<<<<<<<<
neighbor 50.1.0.1 remote-as 200
neighbor 60.1.1.2 remote-as 400

R4(config-router)#DO SH IP INT BR
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 unassigned YES NVRAM administratively down down
Serial0/0 60.1.1.1 YES NVRAM up up
FastEthernet0/1 unassigned YES NVRAM administratively down down
Serial0/1 50.1.0.2 YES NVRAM up up
Serial0/2 unassigned YES NVRAM administratively down down

>>While configuring ebgp multihop on both routers, I simply configured ebgp multihop, instead of ebgp multihop 2. I expected the neighborship to not come up

But it did come up and also, in the configuration, I saw a value assigned to 255 automatically, as I have pasted above.

Is this some implicit rule of ebgp multihop, that an automatic value is assigned if we dont configure it?

[Jon Marshall]

Hop count signifies the number of L3 devices between the EBGP peers. 

As far as I know the default is 255 if you don't configure a value. 

Jon

[balaji.bandi · Accepted solution]

neighbor ebgp-multihop

To accept and attempt BGP connections to external peers residing on networks that are not directly connected, use the neighbor ebgp-multihop command in router configuration mode

neighbor ebgp-multihop XX ( TTL) the range is 1-255.

Cisco document :

https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/26634-bgp-toc.html#ebgpmultihop

There is good thread Peter explain nicely.

https://community.cisco.com/t5/routing/ebgp-multihop-command-only-applies-to-loopbacks/td-p/2030331