Same route distinguishers configured in multiple routers

[DavideRanalli76560]

Hi all,

 I've seen a configuration in which 2 CEs, both peer with PE, but what puzzled me is that both CEs and PE have the same route distinguisher, as apposed to what I thought now I understood that same RD can be configure in multiple routers, I obviously was wrong thinking that RD had to be unique on routers.

But can 2 PE have the same RD configured as well?

Any help would be appreciated

Davide

[MHM Cisco World]

un predictable behavior
so config unique RD for each subnet in PE's.    

[DavideRanalli76560]

Sorry but I understood nothing of what you wrote

[MHM Cisco World]

if you config same RD for multi same prefix

un predicatale behavior

so use unique RD for each prefix in PE's  

[MHM Cisco World]

if you config same RD for multi same prefix

un predicatale behavior

so use unique RD for each prefix in PE's  

[paul driver]

Hello
Route-distinguishers are used  between PE rtrs to make a normal ip prefix originating from its attached CE rtr a unique VPNv4 address as it travels through the mpls cloud as such these a RD's shouldn't be duplicated on different PE rtrs.

[Giuseppe Larosa · Accepted solution]

Hello Davide,

>> But can 2 PE have the same RD configured as well?

Yes they can RD must be unique in a single PE router.

The attempt to add a second VRF using the same RD of an already existing VRF should generate an error like an IP addres overlapping.

One reason to have unique per PE RD values in VPN is for making easier troubleshooting so that it is possible to find out the originator PE by looking at the VPNv4 prefix.

Example : if you use the convention IP address: value you can code RDs using PE-loopback-address:value and using this convention makes very easy to track who is the originator PE of a VPNv4 prefix.

Hope to help

Giuseppe

[paul driver]

Hello
@Giuseppe Larosa  My understanding its to specify an specific RD for each vrf to each PE rtr, But your are saying it is acceptable to have the same RD appended to a VRF on differing PE routers and their VPNv4 prefix would still be unique between each other within the cloud?

Edited - so thinking about what you have stated its only for the simplicity of TS that its preferable to have different RD's for each PE rtr correct?

[Giuseppe Larosa]

Hello @paul driver ,

yes most of first documents on MPLS L3 VPN showed the use of the same RD on multiple PE nodes.

This created a lof of confusion with route target(s) values and goals.

We can say that until there is no overlapping between different sites the same RD can be used re-used on different PE nodes .

The resulting VPN is a collection of VRF sites that share the same route targets values for import and export ( with some differences in more complex services like Hub and Spokes and Central Services).

>> so thinking about what you have stated its only for the simplicity of TS that its preferable to have different RD's for each PE rtr correct?

Yes, with the notable expection of multihomed VRF sites where in order to have the VPNv4 routes generated by both PE nodes accepted and propagated by Route Reflector Server is really a benefit to use different RD.

Routes with the same RD are considered comparable and compared by RRS that would propagate the best path only ( that can end up with the PE with the lowest BGP router-id). Using different RDs on colocated PE nodes make both of their VPNv4 routes propagated.

Hope to help

Giuseppe

[paul driver]

Cheers @Giuseppe Larosa

[DavideRanalli76560]

Very helpful, thank you very much

Davide

[DavideRanalli76560]

very clear explanation, thank you very much

Davide

[DavideRanalli76560]

This answered my question perfectly, very much appreciated

Davide

[DavideRanalli76560]

Thank you for the clear explanation.

[MHM Cisco World]

https://fredrikjj.wordpress.com/2014/07/27/bgp-design-implementation-part-19-rd-and-rt-design/

please see this article, using the same RD in PE.
advantage and dis-advantage