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New Member

Enterprise MPLS

Folks,

This is my senario:

CoreA(6500)-----CoreB(6500)------CoreC(6500)

I have tag-swithcing enabled on CoreA and CoreB as they are my test sites. I DO NOT have tag switching enabled between CoreB and CoreC.

Here is the problem:

When i look at the output of "show mpls forward-table" on Core A, I see a tags for networks hanging off CoreC through CoreB. CoreC has multiple 3550 Layer3 switches hanging off it doing layer 3 routing at the edge.

So when a packet destined to one of the networks hanging off a latey 3 switch connected to coreC leaved CoreA, it has a tag associated with it. When the packet reaches CoreB, the tag is replaced or swapped with another tag even though there is not tag-switching enabled between CoreB and CoreC.

Will the packet be dropped when it reached CoreC as CoreC does not know what to do with the labelled packet? or will it route it now based on its routing table regardless of the tag??

I want to role out enterprise MPLS in my network in a systematic and phases approach and i am having a hard time doing it because of my current topology.

Is there a way i have control what labels get advertised and what labels do not get advertised? any sample configuration would be highly appreciated.

Thanks

4 REPLIES
Cisco Employee

Re: Enterprise MPLS

Parwal,

I doubt the packets would be labeled as they travel from CoreB to CoreC if LDP is not enabled between these 2 routers. You should see the outgoing tag set to "untagged" for the prefixes learnt from CoreC in the output of the "show mpls for" command on CoreB.

Could you provide us with a "show mpls for" from CoreB for one of the prefixes learnt from CoreC.

Thanks,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
New Member

Re: Enterprise MPLS

I will surely do that, thank you very much for responding, in the mean time could you please tell me how to filter and accept certain tags. i would only like to advetise the loopback from coreB to CoreA since that is all i need(I am doing ATOMPLS) for xconnect sessions.

Thanks,

Cisco Employee

Re: Enterprise MPLS

Parwal,

You need to use the "mpls ldp advertise-labels" command to filter labels that and it goes something like this:

CoreA:

!

no mpls ldp advertise-labels

mpls ldp advertise-labels for pfx-filter

!

ip access-list standard pfx-filter

permit

!

For more information on that command, please refer to the following URL:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios123/123cgcr/swtch_r/swi_m2.htm#wp1149769

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
Cisco Employee

Re: Enterprise MPLS

Needless to say you would do the same on CoreB.

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
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