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

Indeed.
Tested with 12.2(15)T17 on 7200s (dynamips):

R2#sh mpls forwarding-table
Local Outgoing Prefix Bytes tag Outgoing Next Hop
tag tag or VC or Tunnel Id switched interface
16 0 10.0.0.1/32 0 Se1/0 point2point

I feel this is better than Untagged too :)

-Carlos
P.S.
For the record, the configuration I used is almost identical to that
that was used by George, just a /32 loopback at R1 and a serial p2p.

George Goglidze wrote:
> Hi Carlos,
>
> I guess we are both right!!!!!!
>
> I just tested it out on GNS3:
>
> Example:
> Just two neighbors, R1 f0/0 --- f0/0 R2
> Very simple topology, connected by F0/0
>
> R1 config:
>
> interface FastEthernet0/0
> ip address 172.16.1.1 255.255.255.252
> duplex auto
> speed auto
> mpls ip
> end
>
> R1#show run int f0/1
> Building configuration...
>
> Current configuration : 93 bytes
> !
> interface FastEthernet0/1
> ip address 10.0.0.1 255.255.255.0
> duplex auto
> speed auto
> end
>
> R1#show run | sec ospf
> router ospf 1
> log-adjacency-changes
> network 10.0.0.1 0.0.0.0 area 0
> network 172.16.1.1 0.0.0.0 area 0
>
>
> ------------------
>
> R2 config:
>
> interface FastEthernet0/0
> ip address 172.16.1.2 255.255.255.252
> duplex auto
> speed auto
> mpls ip
> end
>
> R2#show run | sec ospf
> router ospf 1
> log-adjacency-changes
> network 172.16.1.2 0.0.0.0 area 0
>
>
>
> -----------------------
>
> IMPLICIT-NULL:
>
> R2#show mpls forwarding-table
> Local Outgoing Prefix Bytes tag Outgoing Next Hop
> tag tag or VC or Tunnel Id switched interface
> 16 *Pop tag* 10.0.0.0/24 <http://10.0.0.0/24> 0
> Fa0/0 172.16.1.1
>
> As expected!!!
>
> EXPLICIT-NULL:
>
> R2#show mpls forwarding-table
> Local Outgoing Prefix Bytes tag Outgoing Next Hop
> tag tag or VC or Tunnel Id switched interface
> 16 *Untagged* 10.0.0.0/24 <http://10.0.0.0/24> 0
> Fa0/0 172.16.1.1
>
> --------------------
>
> Tested on:
> GNS3 router model: Cisco 2691
> IOS: (C2691-ADVENTERPRISEK9-M), Version 12.4(5a)
>
> It might show correct label in other IOS versions. this might be just
> some kind of cosmetic bug.
>
> Regards,
>
> On Sun, Dec 26, 2010 at 8:22 PM, Carlos G Mendioroz <tron_at_huapi.ba.ar
> <mailto:tron_at_huapi.ba.ar>> wrote:
>
> Hmm, no.
> Explicit-null would actually use the null (0) tag on the last MPLS hop.
> Explicit-null will just show as 0, AFAIK.
>
> -Carlos
>
> George Goglidze wrote:
>
> I can't check it right now, but I think "explicit-null" label
> would indicate "Untagged" as well in the LFIB.
> Please correct me if I'm wrong.
>
> Regards,
>
> On Sun, Dec 26, 2010 at 2:05 PM, Carlos G Mendioroz
> <tron_at_huapi.ba.ar <mailto:tron_at_huapi.ba.ar>
> <mailto:tron_at_huapi.ba.ar <mailto:tron_at_huapi.ba.ar>>> wrote:
>
> 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 <http://11.1.68.0/24>
> <http://11.1.68.0/24> is locally
>
> connected, and the "next hop" is this router itself.
> The 11.1.6.6/32 <http://11.1.6.6/32> <http://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 <mailto:feeldefreedom_at_gmail.com>
> <mailto:feeldefreedom_at_gmail.com
> <mailto: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 <http://11.1.6.6/32>
> <http://11.1.6.6/32> 0
> Se0/0 point2point
> 17 Pop tag 11.1.68.0/24 <http://11.1.68.0/24>
> <http://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 <http://11.1.68.0/24>
> <http://11.1.68.0/24> is network between R6 and
>
> CE router.
>
> Topology
> ---(R5)----(R6)----(CE)
>
> R6 Lo : 11.1.6.6/32 <http://11.1.6.6/32>
> <http://11.1.6.6/32>
> R6/CE : 11.1.68.0/24 <http://11.1.68.0/24>
> <http://11.1.68.0/24>
>
>
> --
> /Lefe Meedorf/
>
>
> Blogs and organic groups at http://www.ccie.net
>
>
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>
>
>
>
>
>
>
> -- Carlos G Mendioroz <tron_at_huapi.ba.ar
> <mailto:tron_at_huapi.ba.ar> <mailto:tron_at_huapi.ba.ar
> <mailto:tron_at_huapi.ba.ar>>>
>
> LW7 EQI Argentina
>
>
>
> Blogs and organic groups at http://www.ccie.net
>
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
>
>
>
>
>
>
>
>
>
> --
> Carlos G Mendioroz <tron_at_huapi.ba.ar <mailto:tron_at_huapi.ba.ar>>
> LW7 EQI Argentina
>
>

-- 
Carlos G Mendioroz  <tron_at_huapi.ba.ar>  LW7 EQI  Argentina
Blogs and organic groups at http://www.ccie.net