Re: Simple MPLS : Difference between "untagged" and "pop tag"

Pop tag means that the destination (network) is connected to a LSR,
i.e., a router that this router knows that supports MPLS.
This may be because he is receiving LDP from it indicating
"implicit-null" as the tag for this prefix.

Untagged means that the destination is known by some means (routing
protocol?) but the next hop is not MPLS aware (this router is not
receiving MPLS tag info for this prefix) so it will remove the stack
before forwarding.

In your example, the 11.1.68.0/24 is locally connected, and the "next
hop" is this router itself.
The 11.1.6.6/32 is connected to another router and there is no tag info
for this prefix. May be the loopback is a /24 ?

-Carlos

Manouchehr Omari wrote:
> Pop tag means remove the top label and send the remaining payload.
> Untagged means the outgoing interface is not MPLS enabled remove the label
> and send the packet without label.
>
> I recommend you to read "MPLS Fundamentals" which cover these tips in
> detail.
>
> HTH
>
>
> On Sat, Dec 25, 2010 at 9:33 PM, Lefe Meedorf <feeldefreedom_at_gmail.com>wrote:
>
>> Hi,
>>
>> In my simple MPLS setup, I see following entires in "LFIB".
>>
>> R5#show mpls forwarding-table
>> Local Outgoing Prefix Bytes tag Outgoing Next Hop
>> tag tag or VC or Tunnel Id switched interface
>> 16 Untagged 11.1.6.6/32 0 Se0/0 point2point
>> 17 Pop tag 11.1.68.0/24 0 Se0/0 point2point
>>
>> What is the difference between "Untagged" and "Pop tag" ?
>> 11.1.6.6 is R6 (i.e. PE) Loopback 0.
>> 11.1.68.0/24 is network between R6 and CE router.
>>
>> Topology
>> ---(R5)----(R6)----(CE)
>>
>> R6 Lo : 11.1.6.6/32
>> R6/CE : 11.1.68.0/24
>>
>> --
>> /Lefe Meedorf/
>>
>>
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-- 
Carlos G Mendioroz  <tron_at_huapi.ba.ar>  LW7 EQI  Argentina
Blogs and organic groups at http://www.ccie.net