Configure BGP Router ID

[johnlloyd_13]

hi,

just would like to ask what's the best practice in configuring BGP.

i got two new routers and will establish eBGP with an ISP.

my question is, is it good practice to configure a loopback interface and use that as the BGP router ID?

or skip configuring the loopback interface and configure directly the router ID under the BGP routing process?

can i just use the /30 external IP assign by the ISP as my BGP router ID?

i'm also thinking of configure a loopback interface and assign with a public LAN IP assigned by the ISP and use that as router ID? is this the "common" approach?

[Flavio Miranda]

Hi

 For eBGP is not usuall use a loopback interface and this can actually cause you problems making use additional command like update-source. For eBGP with an ISP the IP address on the physical interface between you and the ISP is used to stablish the eBGP peering. The router ID can be the same IP address or not, I dont think this is too relevante.

[MHM Cisco World]

Router ID not need to be reachable IP, 

The must important is update source ip which must be reachable.

So you can use any number. 

But why it sometimes router id important to be reachable?

Because in troubleshooting you can use router-id for ping or tracer router. 

[paul driver]

Hello
The BGP RID is used in best path selection, if you do not hardcode the RID then the router will choose one either by the highest loopback or physically active interface set on the rtr, so letting the rtr to automatically choose its own RID is not recommended as new loopbacks and interfaces can be added as such over time the bgp rid would change, For evpn/ipv6 deployments my understand its even an necessity to manually set a RID, As for ospf its potentially worse as neighbour adjacency's will be torn down and re-established if the RID changed.

So its highly recommended to always hard code the router id, BGP/OSPF.

[Kanan Huseynli]

Hi,

it is recommended to design RID for your all current and future BGP speakers like "ID" in BGP domain (I mean all interconnections) and hard-code them. It is like system-ip from SD-WAN, which indicates unique element in overlay. With hard-coding you will never have chance for different RID which can result confusing while troubleshooting / checking etc.