[c-nsp] MPLS VPN Problem - EoS conflict

E. Versaevel erik at infopact.nl
Tue Dec 23 05:37:08 EST 2008

>From RFC 3032:
          iv. A value of 3 represents the "Implicit NULL Label".  This
              is a label that an LSR may assign and distribute, but
              which never actually appears in the encapsulation.  When
              an LSR would otherwise replace the label at the top of the
              stack with a new label, but the new label is "Implicit
              NULL", the LSR will pop the stack instead of doing the
              replacement.  Although this value may never appear in the
              encapsulation, it needs to be specified in the Label
              Distribution Protocol, so a value is reserved.

Ibrahim Abo Zaid schreef:
> Hi All
> I was implementing MPLS VPN topology and by mistake i was configuring PE-LP
> used for MP-BGP peering with a worng mask /24 instead of /32 (remote PE-LP
> mask is /32) .
> by T.S , i discovered that P router upstream of this PE was dropping
> incoming MPLS packets with the below error message
> tagsw_replace_header: Pkt drop -- EoS conflict, incg label 18 hwinput Fa0/0
> discovering FIB
> 3#sh mpls forwarding-table | in 18
> 18     Untagged      1230       Se0/1      point2point
> so when the mask was /24 , PE advertise label as untag label so incoming
> traffic over MPLS interface will be conveted to IP traffic and looking up in
> LFIB , it will forward it down MPLS interface to PE as native IP packet
> while it should MPLS packet with label-3
> I need to know why that happens ? , does LDP-Adv tells S-bit setting in
> incoming packets according to label type ?
> BTW , the problem solved after changing LO mask to /32 and it has been
> advertised as Imp-Null
> 18     Pop tag      0          Se0/1      point2point
> your responses is highly appreciated
> best regards
> --Ibrahim
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Erik Versaevel

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