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New Member

Cisco ISR G2 and SIP NAT ALG engine core mistake ?

Good morning.

I have following example schema

SIP PHONE -> CISCO 887 -> SIP GATEWAY

1) SIP phone register on SIP gateway and send

REGISTER sip:sip.gateway.com SIP/2.0

Via: SIP/2.0/UDP 10.111.111.6:5060;branch=z9hG4bK-t8pe125htptd;rport

......

2) Everything fine but after packet pass through NAT on Cisco 887 it look like

REGISTER sip:sip.gateway.com SIP/2.0

Via: SIP/2.0/UDP 2.2.2.2:1025;branch=z9hG4bK-t8pe125htptd;rport

.......

but packet itself go from port 1024

Due to it gateway register PHONE in accordance with field VIA and port 1025 and all incoming calls to phone go to port 1025

which never reach phone.

3) looking on nat table

udp 2.2.2.2:1024    10.111.111.6:5060     sip.gateway.com:5060    sip.gateway.com:5060

udp 2.2.2.2:1025    10.111.111.6:5060     sip.gateway.com:5061    sip.gateway.com:5061

udp 2.2.2.2:1025    10.111.111.6:5060     sip.gateway.com:5060    sip.gateway.com:5060

Is it possible to do something to force Cisco router not to do this mess ? I.e not to change port number in VIA header.

Everyone's tags (5)
9 REPLIES
Hall of Fame Super Gold

Cisco ISR G2 and SIP NAT ALG engine core mistake ?

Hmmmm ... I've seen something like this.  Particularly when you run SIP firmwre 9.X.  Downgrade your phone's firmware to 8.X.

New Member

Cisco ISR G2 and SIP NAT ALG engine core mistake ?

Thanks for answer. But it is not related to phones.

It is more related that broken sip alg in lastest version of IOS 15.3

Hall of Fame Super Gold

Re: Cisco ISR G2 and SIP NAT ALG engine core mistake ?

Thanks for answer. But it is not related to phones.

It is more related that broken sip alg in lastest version of IOS 15.3

Errrr ... I don't think so.

I have, at home, CP-7970 and a 880 router.  When I first ran my 7970 with 9.X firmware, it wouldn't register with my Voice SP.  When I did "sh ip nat trans | i " I am seeing the phones trying to go through a port numbers not specified in the SEPmacaddress.xml.cnf.  It was basically shooting all over the place.  My 7960, however, works like a treat.  No problem.

Disabled ALG on the router, still no result.  Enabled port forwarding, doesn't work.

In the end, I downgraded the 7970 to 8.X firmware and rolled-back the changes I made to the router and everything works.

Now, I've got an Asterisk in a Raspberry Pi with my 7970 and a handful of 7960.  Works a treat!

Don't even bother reading this response. 

Hall of Fame Super Gold

Cisco ISR G2 and SIP NAT ALG engine core mistake ?

Leo, from my understanding, the OP is not using a Cisco phone at all.

Hall of Fame Super Gold

Cisco ISR G2 and SIP NAT ALG engine core mistake ?

You're right, Paolo.

Somehow I had the impression he was. 

New Member

Re: Cisco ISR G2 and SIP NAT ALG engine core mistake ?

Thanks for reply.

Sorry but I am really not undertand why you speak about phones . It is BUG in Cisco ios 15.3

Because when i returned to IOS 15.2 all started to work.

I still trying to find out is it possible to force CISCO SIP NAT ALG to be compatible with RFC 3261.

Hall of Fame Super Gold

Cisco ISR G2 and SIP NAT ALG engine core mistake ?

What you should do is to contact the TAC so that the bug in 15.3 can be identified and fixed.

New Member

Cisco ISR G2 and SIP NAT ALG engine core mistake ?

Hi. Thanks again for your answer.

Yeah i understand it.

But for me much better to force router to avoid such behavior at all. Because such SIP ALG issues happens not first time. I seen such issue at least couple of IOS versions. In one version it broken, next fixed,  after couple of monthes they break it again etc.

Hall of Fame Super Gold

Re: Cisco ISR G2 and SIP NAT ALG engine core mistake ?

That is normal with Cisco software.

If you have a version that works, just use it.      

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