Branch office esrst and ITSP issues

[Keith Lawrence]

Hi,

Our branch offices have 5-10 handsets which connect over VPN as part of our overall CUCM environment. To provide resilience and a local PSTN breakout on the sites, ISRs have been installed and configured to connect to a SIP ITSP (Voicehost UK). ESRST has also been configured so the handsets will fail over to SRST mode in the event of head office outage.

We are seeing a problem where handsets in our branch offices are trying to register to our SIP ITSP via the ISR. This is causing problems because the ITSP sees lots of unauthorised connection attempts (in the form HANDSETDN#@voicehost.co.uk) and eventually blocks our IP address.

We have tried to avoid this by configuring the following:

voice register global
 mode esrst
 no outbound-proxy <<---- this command is supposed to prevent proxy registration of handsets i believe
 system message !FAILOVER MODE CALL IT SUPPORT!
 max-dn 20
 max-pool 10

We have also disabled the SRST reference in CUCM for the device pool and applied the config but this doesnt seem to make any difference - the router keeps trying to register the phone DNs with the ITSP directly.

Has anyone seen a similar issue and if so how can we fix it?

[Keith Lawrence]

Okay, googled even harder and it seems SIP SRST and CUBE on the same router is not a supported configuration:

https://supportforums.cisco.com/sites/default/files/attachments/discussion/c0n3wg2wqaaf3pf.jpg

Guess im having to put another router in here just to run SRST then!

[Jitender Bhandari]

Hi Keith,

Your research is 100% correct for 4k platform it does not support any SRST, for ISR G2 it supports only SCCP SRST, i was working with BU on similar query sometime back. I was told that CUBE BU is working on the requirement you might expect something towards the ends of this year (tentative) on this feature. Till then you will have to use another router for SRST.

(Rate if it helps)

JB