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Configuring two SRST refrences (redundant IP WAN routers per site)


I need some advice and best practice guidance, plus some reference material for the following case (novell alert).

Currently we are running a CallManager cluster 4.0(1)SR2a with the publisher and a subscriber in our datacenter. A second subscriber is located at another location (connection between datacenter and co-location is a 10Mbps MAN). This co-location also holds an IPCC 3.5.1 server. Three other co-locations use the cluster resources. All locations use a local gateway to the PSTN. The WAN in between all other co-locations and the datacenter is a MPLS VPN service with different classes of services for call-signaling and RTP streams. Everything is operational and working fine for a couple of years now.

Currently, the IP WAN in not used for intersite RTP streams, but we are in the works of implementing a new MPLS based WAN (new provider) which delivers QoS for less costs which will make intersite dialing over the IP WAN interesting for us. Also, we will have redundancy for the WAN by implementing a second router on a DSL which builds a GRE/IPSec encrypted tunnel to the second router in the datacenter. As a result it is very unlikely that the WAN will fail and that phones will loose connectivity to the CCM cluster. However, for some important sites we will still implement SRST in case the IP WAN fails (very unlikely, but still).

To save costs we want to split the number of e-phones over the two routers (otherwise the required platforms are to excessive) and as far as we understood so far this should be possible. However, documentation and best practice information is quite hard to find (and believe me, I've tried).

So far I figured that to achieve this I will need to configure two SRST references in CallManager and split the phones into two device pools. Then associate the two different SRTS references which the two devicepools to achieve the SRST split. This is the easy part, but now the hard part. Only one router holds the BRI or PRI interfaces to the PSTN so I need to setup dialpeers on the routers in order to get everything to route correctly while in SRST. So, the main question is, what would be the best practice and needed dialpeer configuration to achieve this?

Another thing I am strugling with is the phone load that I will need. We will be running IOS 12.4(6)T on the routers, so this is SRST 4 (if I am not mistaken). This together with CCM 4.0(1)SR2a, what would be the best phoneload for the 7940, 7960, 7920 and 7936 phones?

Any other information for guidance in this setup will be highly appreciated.

Kind regards,


Community Member

Re: Configuring two SRST refrences (redundant IP WAN routers per


You're on the right track in that you'll have to have two device pools for the site to be able to split up the SRST load. If possible, try to make the extensions on each of the routers similar so you can easily add VoIP dial-peers to enable extension to extension dialing as well as to easily be able to route inbound calls.

On the router w/o the PSTN connection, you're going to have to create your same local, LD, international, services etc etc dial-peers. The only difference is that they'll be voip dial-peers pointing over to the router with the PSTN connections.

I'm attaching a config example you can try. I just free handed please excuse any typos.

As for the code versions, just make sure you keep your CallManager updated with the latest devpak's and you won't have to worry about anything further.

Let me know if I can help anymore.


Re: Configuring two SRST refrences (redundant IP WAN routers per

And that while I never followed any IPT course, I just love CCO, everything is so well documented :-))

Anyway, you reply confirmed what I was already thinking and I am very happy to have that verified (thus I rated your reply). I expected that it woudl be advisable to keep the extension in a range to make dialpeer configuration more easy.

About the phone loads, I figured that it would not matter, but just wanted to verify. I just tested the latest (version 8) load with one 7940 and it upgraded perfect without any issue.

Again, thanks for the quick and excellent reply!


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