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Router Reload during SRST failover


We run a centralized call manager environment with H.323 gateways to remote voice routers.  When the WAN fails the phones go into SRST and register with the router.  Rebooting the router during an SRST event seems to break SRST.  After the reload the phones do not register with the router.

What are the possible causes of this?  I'm not able to review a remote router while the WAN is down and haven't been able to troubleshoot the issue. 

The phone DHCP server is remote, but a router reload would not cause the phones to lose their IP configurations right?

The router initially connects to call manager to get the phone configuration, are the phone configurations stored in flash?  Does the router need to reconnect to call manager foloowing a reboot in order for SRST to work correctly?

Any help is appreciated,


3 Replies 3


What model phones are you using?  I found CSCue91938 (Registration failed if reset phone while it is on SRST).  This only affects the 8961/9951/9971s though.

Gregory Brunn

This sounds very strange indeed.

Sounds like something with SNAP Simple Network Auto Provisioning.  Are you using SRST or CUCM express in SRST mode?

When an SRST enable gateway detectes newly registered ip phones because of a WAN outage the gateway will query the ip phone for their configuration and then autoconfigures itself. 

SNAP is used to autoconfigure the branch office router to provide call processing for phones registered with the router.

I wonder if setting up CUCM express in SRST mode will get ride of this problem as the configuration can be pre-done and not done through SNAP.

Once again this just a theory.  Might be worth trying?

Brian I tried to reference you bug however access denied. Is this something that is not externally facing yet?

Also in regards to a question in the orginal post.

The phone DHCP server is remote, but a router reload would not cause the phones to lose their IP configurations right?

It may if you are using a ISM or SM to power your phones.   On small branch offices CME delpoyments I have worked on with ISM or SM if you reloaded the router you brought down the whole site.  So yes IP configurations would be lost however if you had an external switch your phones would stay up and keep ip address information.   Can you confirm that you have an external switch?

The switches are external to the router, the phones shouldn't be rebooting. 

Here is the SRST configuration:



max-conferences 5 gain -6

transfer-system full-consult

ip source-address port 2000

max-ephones 25

max-dn 150 dual-line


I will do more testing on this next week, we are rolling another office over to Cisco Voice so I can test while there.  I need to see what is going on after the router reloads.

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