01-30-2013 01:41 AM - edited 03-04-2019 06:53 PM
When to tags and BGP communiyu values get stripped off in a MPLS environment.
So for example on a PE router if a tag or BGP community value is set on incoming routes from a CE, would this be propogated throughout the MPLS network or would it be local to that device and get stripped of once its routed through the core network.
Can either of these (tags/communities) be propgated through multiple AS networks, so for example set a tag/community on the CE, honour on PE, route through MPLS to remote PE into another MPLS network. At what point do these get stripped off.
thanks
01-30-2013 01:54 AM
Hello Ahmed,
BGP normal communities and BGP extended communities like route targets can both be propagated if PE devices have a configuration for address-family vpnv4 that allows for this
router bgp AS
address-family vpnv4
send-community both
with both normal and extended communities are propagated.
If at SP AS border the same is done BGP standard communities and BGP extended communities can be extended also.
For route-targets in inter-AS VPN sometimes the ASBR performs route target rewrite at border.
Hope to help
Giuseppe
01-30-2013 05:52 AM
Thanks,
What about route tags set via a route map, can they be propogated.
01-30-2013 06:08 AM
Hi,
not supported, I'm afraid.
When you try to apply
neighbor x.x.x.x route-map map-with-tag out
you get an error message:
% "tag" used as BGP outbound route-map, set tag not supported
BR,
Milan
02-01-2013 12:22 AM
Thanks.
So i suppose then if a tag was set on an incoming route, it would be stripped out when routed within MPLS or to another EBGP peer.
02-01-2013 01:24 AM
Hi,
if you try to use set tag command within a route-map applied as incoming route-map on a BGP neighbor or a route-map applied when redistributing IGP into BGP, you always get the same error message:
"..., set tag not supported"
So IMHO route tagging is not supported at all in BGP, you need to use BGP communities instead.
BR,
Milan
02-01-2013 03:16 AM
Hello Ahmed,
as Milan has noted when dealing with BGP we should or actually must use BGP communities instead of route tags.
If PE-CE protocol is not eBGP you may need to use route tags with IGP, but then the route tag is NOT propagated to MP BGP as it would be a BGP community with appropriate configuration.
The PE router might be configured to add BGP communities based on route tags but it is not straightforward.
By the way, BGP communities are more powerful then route tags as multiple BGP communities can be associated to a single NLRI prefix.
Hope to help
Giuseppe
04-24-2013 01:03 AM
I am looking for an IOS code snippet that would show how a BGP community value can be "transferred" into the MPLS area so that it can checked.
Thanks,
Hank
Discover and save your favorite ideas. Come back to expert answers, step-by-step guides, recent topics, and more.
New here? Get started with these tips. How to use Community New member guide