Cisco SPA3xx/5xx freeze - SOLVED!

[Alex A. Welzl]

We had experienced the well-known freezing of SPA phone (3xx/5xx) in our environment. It happened everytime when a phone looses its connectivity to the SIP proxy. After googling a lot with many attempts but no real solution, we started digging into the issue. First we were testing different firmwares - no difference in behaviour, then we started with an try-and-error approach. There we found out that the NAT Keep-Alive setting was the source of the trouble. As soon as we disabled the Keep-Alive setting the phones did not freeze at all. We assume that the phone has a buffer overrun when no keep-alive message could be sent out successfully.

[Dan Lukes]

Not so much details, unfortunately. It would be nice to know how long the connectivity needs to be lost, also, captured syslog&debug as well as SIP messages will be valuable.

I has been never affected by the issue you described, despite we have hundreds phones deployed with Keep-Alive turned on all the times. So either our connectivity outages are so short or issue depend not only on Keep-Alive but on something other as well.

Despite of it, thank you for your report, it may help.

[Steven Howes]

Interesting! We've seen this a fair bit (if you lose sight of the network but the link stays up then it's quite reproducible). On firmware newer than 7.5.4 we can do it almost every time (we've stopped moving forwards with firmware until we could identify it). I'll do some work in my test environment and see what happens.

[Dan Lukes]

Our current settings (used with 7.5.6 & 7.5.7 firmware):

SIP->NAT Support Parameters
Handle VIA received:	Yes	Handle VIA rport:	Yes
Insert VIA received:	Yes	Insert VIA rport:	Yes
Substitute VIA Addr:	No	Send Resp To Src Port:	No
STUN Enable:	No	STUN Test Enable:	No
STUN Server:		EXT IP:
EXT RTP Port Min:		NAT Keep Alive Intvl:	55
Redirect Keep Alive:	No

Ext N -> NAT Settings
NAT Mapping Enable:	No	NAT Keep Alive Enable:	Yes
NAT Keep Alive Msg:	$NOTIFY	NAT Keep Alive Dest:	A.B.C.D