BGP route identification

[rashad_cisco]

Hi Guys,

recently I have noticed such strange inconsistency regarding BGP route-id selection in IOS-XE, NX-OS and IOS-XR.

In all official Cisco.com documents they say it is based on highest IP address of loopback ip address but "Troubleshooting BGP: A Practical Guide to Understanding and Troubleshooting BGP published 2016"  book says it based on lowest ip address of loopback for  NX-OS and IOS-XR.

Could you anybody explain it ? or faced such inconsistency previously ?

BR

Rashad Yarammadov

[Georg Pauwen · Accepted solution]

Hello,

I think the below explains it:

BGP Identifier
The BGP Router-ID (RID) is a 32-bit unique number that identifies the BGP router in
the advertised prefixes as the BGP Identifier. The RID can be used as a loop prevention
mechanism for routers advertised within an autonomous system. The RID can be set
manually or dynamically for BGP. A nonzero value must be set for routers to become
neighbors. The dynamic RID allocation logic varies between the following operating
systems.
■ IOS: IOS nodes use the highest IP address of the any up loopback interfaces. If
there is not an up loopback interface, then the highest IP address of any active up
interfaces becomes the RID when the BGP process initializes.
■ IOS XR: IOS XR nodes use the IP address of the lowest up loopback interface. If
there is not any up loopback interfaces, then a value of zero (0.0.0.0) is used and
prevents any BGP adjacencies from forming.
■ NX-OS: NX-OS nodes use the IP address of the lowest up loopback interface. If
there is not any up loopback interfaces, then the IP address of the lowest active up
interface becomes the RID when the BGP process initializes.

[rashad_cisco]

Hello Georg,

thanks for your reply.

I agree with you according the mentioned Cisopress book but in the following cisco.com document claim otherwise:

https://www.cisco.com/c/en/us/td/docs/iosxr/cisco8000/bgp/70x/b-bgp-cg-8k-70x/b-bgp-cg-8k-70x_chapter_01.html#concept_h2g_bb3_mjb

Br

Rashad