SRST and HSRP

[MLADEN MILANOVIC]

Hi,

is it possible to have two or more SRST routers on the remote location which will be in the same HSRP group. IP address of the virtual router should be configured in the CCM on the central location in the SRST reference field. PSTN trunks on the remote locaton will be equaly distributed on the routers in the same HSRP gorup. Idea is that we have full redundant solution during the WAN outage. If active SRST router fails during the WAN outage standby router will take signalisation for the IP phones on the remote location.

What you think about this design/concept. In fact does someone did some testing of this configuration or mabye someone has an instalation with this design ?

Thanks.

Mladen

[allan.thomas]

CallManager 3.3 introduces SRST references, have you considered configuring separate device pools which have a different SRST reference.

Remember depending of the specification of the router you are using for SRST you are limited to the number of Phones, and DNs you can have registered. With two devices pools for example each pointing to a different SRST gateway you will be able to divide the IP Phones between them.

Further resiliency can be added by configuring pots dial-peers with different preferences for directly connected trunks, and a single VOIP dial-peer (last preference) of the other PSTN trunk on the other SRST gatway as a last resort.

For example: If you have two SRST gateways, with an equal number of E1 trunks, you can configure two pots dial-peers as follows:

dial-peer voice 1000 pots

preference 1

incoming called-number .

destination-pattern 9T

translate-outgoing calling 1

direct-inward-dial

port 1/0:15

!

dial-peer voice 1001 pots

preference 2

incoming called-number .

destination-pattern 9T

translate-outgoing calling 1

direct-inward-dial

port 1/1:15

As a last resort if both the local trunks are down,the third preference is the other SRST gateway which will have similar pots dial-peers for directly connect E1 trunks.

dial-peer voice 1002 voip

preference 3

destination-pattern 9T

session target ipv4:192.168.1.254

dtmf-relay h245-alphanumeric

no vad

Hope this helps.

[MLADEN MILANOVIC]

Allan,

thanks on your reply. This is a good idea and standard design approach, but if the main SRST router fails IP phones which are on that router stays without service.

If we have HSRP and two SRST routers in that case if one of them fails second router will take all signaling between phones.

Anyway, this is the teory and I was wondering did someone really tries that. If not I will arrange lab testing and I'll inform the community about results :-)))

Thanks again and have a nice day,

Mladen

[allan.thomas]

Unfortunately I have not come across this particular design, and not entirely sure of the implications of using a virtual address instead of a real address for the fallback ip source-address.

I agree with the concept, however the only reference I can find regarding HSRP fail-over and IPT deployments is for CAC/Gatekeeper control.

As I have mentioned earlier, the only other main consideration with this deployment, is the specifications of SRST, in particular the max number of ephones and dn's you can have registered with a single gateway at anyone time.

The most scaleable platform is either the 3660 or 3745 supporting upto 240 phones and 960 dn's. More information regarding the specifications for SRST version 3.0 can be found at the below url.

http://www.cisco.com/en/US/partner/products/sw/iosswrel/ps5012/products_feature_guide_chapter09186a0080181320.html#wp1376270

I would be interested to know how the testing goes.