Need to simulate WAN failure to test SRST

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Jan 29th, 2008
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I have a centralized CCM deployment with a pub and sub.

In a remote office, it is not possible for me to take down the WAN to test SRST. What is the simplist way to do this?

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dezoconnor Tue, 01/29/2008 - 06:40
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You could stop the CCM service on your Pub and Sub but this would affect all your telephony users across all your sites.

Best way is to have your local IT at the remote sites just simply disconnect the WAN link. You're going to need someone on site to make test calls anyway!

hauchinango Tue, 01/29/2008 - 06:48
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I am at the remote site. I cannot bring down the WAN link, but I may bring down the voice in order to test SRST. I cannot stop the ccm service becasue this will affect all locations.

I am just looking for an easy way to simulate WAN failure at the far end.

chris.mann Tue, 01/29/2008 - 06:49
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Depending on your WAN design, you could maybe just break the IP Routing between the voice vlan at the site, and your call managers. That would leave your data traffic up, and not interrupt your users there, but the phones would be forced to fail over to srst.

Jon Nelson Tue, 01/29/2008 - 09:22
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Create an ACL on the remote router that blocks traffic coming from the PUB/SUB. This way it only affects voice traffic. Make sure you keep an allow for other traffic as you don't want to lock yourself out completely!


Thank you,

Jon Nelson

mattcalderon Tue, 01/29/2008 - 11:34
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Just to add on to the good info from Jon, you can simulate SRST for one phone only by using an extended ACL and block traffic from the pub/sub to the ip of the phone itself.


pcameron Tue, 01/29/2008 - 13:45
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There is an even simpler method ... On the actual WAN router, use an host ip route for the CCM IP address and send it to null0.

ip route null0

ip route null0

Any traffic for the Pub/Sub will be sent to the router's bit bucket, so the all traffic to the CCM is blocked, and the devices loose keepalive responses.

All other services on the router remain unaffected. This allows you get around issues with incorrect access lists blocking all traffic to the router (it happens all the time...)

The only caveat with doing this - be VERY CAREFUL if you are running a routing protocol and you have the command 'redistribute static' - you don't want your entire network's traffic learning about this low cost route and then having all packets for the CCM dropped!

guy.richard Fri, 02/01/2008 - 00:31
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What I do is olso affecting routing but I do it to the IP Phone I want to test SRST to.

On the central router or L3 switch I add a route /32 to null0 for one or two Ip Phones I want to prevent seeing the CUCM. Fri, 02/01/2008 - 00:47
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stop stop stop bunny :)))

only thing.that you should to do is

access-list 111 deny tcp "you internal network ip range" host CCMIP eq 2000

access-list 111 permit ip any any

so you block SCCP port

and add ip access-group 111 in to you desired interface, thats all. Everything is working

jason-calbert_2 Fri, 02/01/2008 - 12:43
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If the phone is in the same subnet as the SRST router just change the default gateway on 1 particular phone to point to a fake IP address. This way the phone can't reach callmanager and will unregister. The phone will then try and register with SRST

Using this method you can test just one phone without having to take down all voice at this site.

Just something I use and thought might be helpfull to you



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