10-18-2020 06:45 AM
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
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10-18-2020 11:28 PM
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
10-18-2020 06:50 AM
un predictable behavior
so config unique RD for each subnet in PE's.
10-18-2020 07:33 AM
Sorry but I understood nothing of what you wrote
10-18-2020 03:57 PM
if you config same RD for multi same prefix
un predicatale behavior
so use unique RD for each prefix in PE's
10-19-2020 04:39 AM
if you config same RD for multi same prefix
un predicatale behavior
so use unique RD for each prefix in PE's
10-18-2020 10:18 PM - edited 10-18-2020 10:19 PM
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.
10-18-2020 11:28 PM
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
10-18-2020 11:40 PM - edited 10-18-2020 11:44 PM
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?
10-19-2020 01:08 AM
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
10-19-2020 01:19 AM
Cheers @Giuseppe Larosa
10-20-2020 06:59 AM
Very helpful, thank you very much
Davide
10-20-2020 07:03 AM
very clear explanation, thank you very much
Davide
10-20-2020 07:06 AM
This answered my question perfectly, very much appreciated
Davide
10-22-2020 08:51 AM
Thank you for the clear explanation.
10-20-2020 08:49 AM
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
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