RE: MPLS VPN Label

        The prefix itself doesn't have two labels, the actual packets in the data plane will have two (or more) labels. The VPN label is the bottom-most label, not the top label. The top label is usually the transport label that is derived from LDP. In short the transport label tells the MPLS cloud which PE router the packet is destined to, then once it arrives there the VPN label tells the PE which CE facing interface the packet is destined to.

        On the PE routers you can see what the VPN label is by issuing the "show bgp vpnv4 unicast all w.x.y.z", where w.x.y.z is the VPNv4 prefix in question. In the actual MPLS cloud you can see both the transport (topmost) label and the VPN label by looking at the "debug mpls packet" output.

        "untagged" and "no label" mean the same thing, that the packet will be forwarded out an interface that is not running MPLS, or does not have a label binding to that prefix. For the PE to CE link this is normal, because the CE is not running MPLS.

        For more detail check this video on MPLS Layer 3 VPN Verification & Troubleshooting: http://goo.gl/Ys0lF

HTH,

Brian McGahan, CCIE #8593 (R&S/SP/Security)
bmcgahan_at_INE.com
 
Internetwork Expert, Inc.
http://www.INE.com

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of Naufal Jamal
Sent: Friday, June 24, 2011 2:26 PM
To: ccielab_at_groupstudy.com
Cc: rahula_at_hcl.com
Subject: MPLS VPN Label

Hi,
I have set up a MPLS VPN network and my end-to-end ping works fine over the
MPLS. Ie I can ping CE1 from CE2 and vice-versa. I need to understand few
things regarding MPLS VPN label.
It was written on the books that the prefixes carry two labels with them while
traversing through the MPLS network with VPN label being on the top. Can we
see the VPN label for any prefix in the P routers?
PE1(config-router)#do sh mpls forwarding-tableLocal Outgoing Prefix
     Bytes tag Outgoing Next Hoptag tag or VC or Tunnel Id
 switched interface19 Untagged 1.1.1.1/32[V] 3762 Fa0/0
 10.10.10.1
Why the outgoing tag is mentioned as Untagged. 1.1.1.1 is my route in CE1
router which is inside the vrf.
PE1(config-router)#do sh ip bgp vpnv4 all labels Network Next Hop
   In label/Out labelRoute Distinguisher: 100:100 (ABC) 1.1.1.1/32
10.10.10.1 19/nolabel
Why is "nolabel" mentioned as the Out label here?
Please help me understand.

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Received on Fri Jun 24 2011 - 15:15:46 ART