Recursion Against IPv4+Labels prefix learned via iBGP

Unanswered Question
Dec 21st, 2009


Due to a number of reasons we have a rather unique requirement to use IPv4+labels as a means to install a BGP next-hop against which other labelled BGP routes can be resolved.  Though this sounds fairly complex I was hoping to acheive this as follows, (basic example):

R1 (loop0 = a, loop1 = b) <---- -----> R2 (loop0 = y, loop1 = z)

There is an IGP session between R1 and R2, whereby loop0 and the inter-link are inserted into the IGP, a BGP IPv4 + labels session is established between loop0's (a and y), over this session R1 advertises b --> R2, and R2 advertises z --> R1.  Using route-maps, further labelled prefixes advertised between R1 and R2 have the BGP next-hop modified to b and z respectively.

Everything looks as I would expect, labels advertised / received as I would expect, (RIB entires etc), however, CEF shows recursion issues.  I have tried various IOS images but same (or similar) behaviour.

Should this work.. All CCO references to IPv4+labels (unless related to IPv6 prefix / path distribution) explicitly state eBGP IPv4+labels, but our requirement is for IPv4+labels in conjuction with iBGP.

(If I try a similar schema using LDP - this works fine, but unfortunately LDP is not an option in the production network).

Also note, the link between devices is Ethernet,

I can appreciate why this may not work, but conversely I see no reason (except implementation) why this will not work.

Can someone please confirm whether this should work, and if so which version of IOS for the C7200.

Thanks.  Simon

I have this problem too.
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s.millar Tue, 12/22/2009 - 04:31

Now works fine with a static mpls bindings for a and y, set to phy intf address(s) with implicit-null.

Laurent Aubert Tue, 12/22/2009 - 10:53

Hi Simon,

BGP IPv4 + Labels relies on a MPLS aware core (BGP free core usually) so you need a label associated to your loopback 0. You used static mapping but LDP will do the job as well.




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