MPLS TE FRR on Cat 6500 GigabitEthernet convergence ?

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Jan 31st, 2006
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Someone can explain me about convergence time (50 ms or others ?) on Cat 6500 with GigabitEthernet Interfaces using MPLS TE FRR with 12.2.18SXD1 or later ?

We have these line cards and sups:




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mheusinger Wed, 02/01/2006 - 00:31
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there are mainly two contributions to FRR convergence time as far as I know.

First you have to detect the failure, second the router switches over to the predefined backup LSP.

The second portion is only a local rewrite of the LFIB and should be practically instantaneous.

The first one - failure detection - is the major contribution. In SONET/SDH a failure condition in the optical network is propagated in certain bytes in the SONET/SDH frame header, thus it is rather quick to detect failures.

With ethernet that might be different. Assume two routers connected through a LAN switch. In this case a link-down event in one router will only be detected by means of keepalives. Those might be your routing hellos or in MPLS TE also RSVP messages. With standard timers that means several seconds.

In case you have back-to-back fibers then the convergence time will be considerably lower. You should be able to reach less than a second, but I have not measured this myself - this is "second hand" information.

Another option to look at: f.e. in IS-IS we can lower keepalive timers to less than a second and hold timer to one second. This should be designed carefully not to introduce unwanted instability into your routing.

In any case you cannot reach 50ms IP routing convergence time.

The question should really be, which convergence time is acceptable in your environment, i.e. which applications require less than a second outage and whether it will justify the efforts.

Hope this helps! Please rate all posts.

Regards, Martin

infotn-cco Thu, 02/02/2006 - 02:56
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thanks for your response.

So do you think we can't obtain 50 ms of convergence using MPLS FRR TE w RSVP with gigabit ethernet link and cisco 6509-NEB-A switch (SUP 720 3BXL and WS-X6724-SFP) ?

We have one metropolitan ring with 8x1gbps link gigabit ethernet (MPLS, OSPF for IGP and MP-BGP).



mheusinger Thu, 02/02/2006 - 05:00
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I did not test your specific equipment. I am just cautious in stateting some values I haven´t tested myself or am sure of.

But in case you have the switches connected back-to-back you could possibly reach the 100 ms range.

I know of another network which gets 50-100 ms switchover time with GE and FRR using different hardware.

Hope this helps! Please rate all posts.

Regards, Martin


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