Fast Switching

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Dec 11th, 2007
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Good day I just have a quick question...I have a point to poing frame relay connection and I want to enable fast switching at the distant end. If I do that is there a possibitlity of disconnecting myself from the distant router? Also would I need to enable fast switching at the near router as well?

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Hi, have you checked to see if fast switching was turned off on your interfaces? fast switching is enable by default on all interfaces that support fast switching. As long as the badwidth is more than 64k shouldn't be no problem.

I dont think you would get disconnected from your distant router with fast switching, you might see an increase in packets drops because the local interface cant process the packets fast enough.

Use the "show IP cache" command to see the fast switching cache.

use "ip route-cache" to enable fast switching.

Have a look at the document below for more information.


wgranada1 Wed, 12/12/2007 - 06:29
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Yes the fast switching is disabled I wanted to enable it as we are doing compression on the distant end router which is kind of sluggish I'm hopeing that fast switching will help out.

bvsnarayana03 Tue, 12/11/2007 - 21:07
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To add to what williams explained, also chk the output of "sh interface stat". Check the pkt in & out against route-cache under the switching path. If there are matches to pkt in & out, then your fast switching is working.

also chk output of "sh ip cache", if fast switching is enabled you'll se entries in table with prefix, next-hop & interfaces.

hope that clarifies.

pls rate all helpful posts.

wgranada1 Wed, 12/12/2007 - 06:32
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Thanks for the info I will try it out, I checked both ends of the connection and fast switching is disabled on both sides. So inorder for this to work properly I'm assuming that I need to enable fast switching on both ends, the near and distant end serial interfaces correct?

Richard Burts Wed, 12/12/2007 - 06:36
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Here are a couple of things about your questions. If you enable fast switching on the remote end it should not (if it is the only change) have any potential to terminate your connection.

You can enable fast switching on one end but not the other (if that is what you want to do - but why would you want to force process switching?).

Depending on the type of router and especially depending on the version of code running you may be running (or able to run) CEF forwarding in which case CEF is better than fast switching.

If you are doing compression in software (and we can not tell from your post whether it is or not - but I assume that it is) then you are effectively processing switching anyway since the router CPU must process each individual packet. So fast switching may not matter.



wgranada1 Wed, 12/12/2007 - 06:46
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Hi Rick thank you for that I wasn't sure if I would get disconnected or not.

I noticed that the near end has fast switching enabled while the distant end doesn't so I wanted to enable that so both ends are the same.

I have a 2811 running 12.4(9)T3 running software compression I notice that the CPU utilization is high and the preformance of the router is sluggish that is when I noticed

that fast switching wasn't enabled on the distant end and I wanted to enable it to see if that would help in preformance. So what you are telling me is that I'm better off using CEF forwarding instead of fast switching as that will not help out with the preformance due to I'm using software compression? By the way I also see that CEF switching is disabled as well if I enable that do I need to enable as well on the near end? Thanks Rick for your input!!!!

wgranada1 Wed, 12/12/2007 - 06:38
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Hi guys thanks for the info I have answered my own question about enabling fast switching on both ends. I check to see if fast switching was enable on the near end router and it is but the distant end router fast switching is disabled so I think that is the root cause of why the performance on the distant end router is sluggish. I will enable fast switching on the distant end router and see if that helps and will let you guys know.....thanks so far for all your help!!!

wgranada1 Mon, 12/17/2007 - 08:15
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It appears fast switching doesn't help with compression as when I do a show interfaces switching the only thing I see is process switching no packets are fast switching. I guess my next step would be to enble CEF on the distant end router as well as the local end to see if that helps out.


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