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New Member

Tag-switching config doubt

Hello everybody,

I would like to get some advise in a tag-switching config in order to perform a testing: I have a Cisco 12012 and a Cisco 7507 each with a GigE interface. I would like to establish several tdp sessions using this single interface. I was thinking in creating sub-interfaces and to add a dot1.q vlan tag to each of them and then to configure tag-swithching in all of the sub-interfaces. I wonder if this might work.

I cannot perform this test right now since I have my equipment in different sites so if I am certain of this to work I might transport them.

I would appreciate any help!! :)

Thanks in advance,

Regards,

Nataniel

7 REPLIES
Cisco Employee

Re: Tag-switching config doubt

You will only have one TDP (or LDP) session between two routers, no matter how many interfaces you have between these two routers.

So even if you were to create several dot1q subinterfaces between the two routers, only one TCP session would be created.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
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Re: Tag-switching config doubt

Hi,

what Harold pointed out is because in frame-mode MPLS you have one label space per platform (A.B.C.D:0) and there is only one TDP/LDP TCP session per address space.

In case you have an ATM network and configure cell-based MPLS you could end up with several TDP/LDP sessions between two routers.

Anyhow, I am assuming you are not really intersted in several LDP sessions but in MPLS forwarding (label switching) across several interfaces. If my assumption is true, please be aware that you would need 3 routers or - because of penultimate hop popping - you would need MPLS VPN to see labeled packets crossing the interfaces.

Hope this helps

Martin

P.S.: please rate helpful posts.

New Member

Re: Tag-switching config doubt

Thanks Martin, thanks Harold,

In fact what I want to achieve is to establish several (as many as possible) tdp sessions among my 12K and any other Cisco router, so I am not seeking for the label switching functionalities.

Soon after I posted my message I created in my lab a FE back to back connection among two 7507s and configured as I said: sub-interfaces tagged with dot1q and added a /30 in each of them. Afterwards I configured tag-switching in all the subinterfaces and could see that the tdp sessions were created. Certainly I did not verify the TCP sessions linked to the tdp sessiones neither did debugging to see messages but I think that this scenario might work for what I want: to give some stress in tdp sessions to my 12K as I have in production.

Our core is based in 12Ks and runs tag-switching so I am figuring out how to test a migration scenario towards mpls, this is my final goal. I want to observe a 12012´s performance while handling tdp and ldp sessions at the same time. ANY SUGGESTIONS? :)

Thank you guys!

Regards,

Nataniel

Re: Tag-switching config doubt

Hi Nataniel,

as written above there will be only one LDP TCP session per neighbor in frame-mode MPLS. So this means you can increase the number of hellos produced, but not really an LDP stress test. What you could do is to take a route generator and flood the IGP with a number of routes equal to the one in your backbone, as for every IP route in IGP LDP has to choose a label and advertise it. Then tear down the session and check what happens.

But generally LDP creates not a lot of stress to your router as it only sends hellos unless IGP changes occur. In this case IGP calculation would presumably stress much more than LDP.

Hope this helps

Martin

New Member

Re: Tag-switching config doubt

Thank you Martin,

you are totally right.

Do you happen to have any documents, URLs where I could read about migrating a Tag-Switching network towards MPLS?

Thanks a lot!

Regards,

Nataniel

Re: Tag-switching config doubt

Hi Nataniel,

with "converting tag-switching to MPLS" you mean converting from TDP to LDP? This is rather simple.

a) mpls label protocol both on all relevant interfaces

b) wait until LDP is converged (TDP and LDP will advertise the same Labels)

c) mpls label protocol ldp on all relevant interfaces

You should not even loose a single packet as the CEF tables should not change. But as always: test before implementation.

Regards

Martin

New Member

Re: Tag-switching config doubt

Again, thanks a lot Martin!

Regards and Merry Christmas!!

Nataniel

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