From: Brian McGahan (bmcgahan@internetworkexpert.com)
Date: Sun Nov 26 2006 - 12:39:21 ART
You need to look at two things, your IGP bound labels and your
BGP bound labels. The IGP bound labels in the "show mpls
forwarding-table" will show you the label you use to get to your BGP
next-hop. The BGP bound label will show you the VPN label for the final
destination inside the VRF.
In the below output R4 has a route for 10.1.77.0 in VRF "VPN_B".
The next-hop of 10.1.77.0 is 13.1.1.1:
Rack1R4#show ip route vrf VPN_B | in 10.1.77.0
B 10.1.77.0 [20/1] via 13.1.1.1, 4d11h
The VPN label for 10.1.77.0 is 19:
Rack1R4#show ip bgp vpn vrf VPN_B labels | in (Out
label|Distinguisher|10.1.77.0)
Network Next Hop In label/Out label
Route Distinguisher: 100:2 (VPN_B)
10.1.77.0/24 13.1.1.1 nolabel/19
The IGP label for the next hop, 13.1.1.1, is 21:
Rack1R4#show mpls forwarding-table | in (Local|interface|13.1.1.1)
Local Outgoing Prefix Bytes tag Outgoing Next Hop
tag tag or VC or Tunnel Id switched interface
20 21 13.1.1.1/32 560 Se0/0 34.1.24.2
This means that when R4 sends traffic to 10.1.77.0 inside VRF
VPN_B it will be encapsulated with the VPN label 19, then
re-encapsulated with the IGP label 21. Debug output on the next hop
router (34.1.24.2) verifies this:
Rack1R2#debug mpls packet
Packet debugging is on
Rack1R4#ping vrf VPN_B 10.1.77.7
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.1.77.7, timeout is 2 seconds:
Rack1AS>2
[Resuming connection 2 to r2 ... ]
MPLS turbo: Se2/0: rx: Len 112 Stack {21 0 255} {19 0 255} - ipv4 data
The point is that as long as everyone in transit path knows how
to get to 13.1.1.1 they don't need to know how to get to 10.1.77.0
because they are only label switching the traffic towards the BGP
next-hop.
HTH,
Brian McGahan, CCIE #8593 (R&S/SP)
bmcgahan@internetworkexpert.com
Internetwork Expert, Inc.
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> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> Bozhidar Batev
> Sent: Sunday, November 26, 2006 6:58 AM
> To: ccielab@groupstudy.com
> Subject: MPLS VPN
>
> Hi,
>
>
>
> If I have MPLS VPN scenario how can I see what label PE assigns to the
> MPLS VPN tunnel. Documentation said that when MP-BGP is encapsulated
in
> MPLS packet, this packet has two labels. I cant find any command to
show
> me this tow labels. I'm not sure that I really understand the purpose
of
> the two labels. Thanks a lot.
>
>
This archive was generated by hypermail 2.1.4 : Fri Dec 01 2006 - 08:05:48 ART