[VoiceOps] Cisco 7941 SIP

Kumudu Suriyaarachchi ksuriyaarachchi at alteva.com
Tue Oct 6 18:58:05 EDT 2015

Two things I would try

1.      Point the phone to alternate port (5090) . You will need a realm configured on the HNT SBC to accept 5090

2.      Downgrade the phone firmware

Kumudu Suriyaarachchi    ksuriyaarachchi at alteva.com<mailto:ksuriyaarachchi at alteva.com>
P 484.534.4427


From: VoiceOps [mailto:voiceops-bounces at voiceops.org] On Behalf Of Pete E
Sent: Tuesday, October 06, 2015 5:10 PM
To: voiceops at voiceops.org
Subject: [VoiceOps] Cisco 7941 SIP

Greetings Voice Operators,

We have an interesting (code word for annoying) challenge that we've never dealt with before, probably because we don't do much with Cisco phones. We have a new customer coming on who wants to keep their very old Cisco 7941 phones. They have a few offices and the phones work as expected behind an Edgemarc. However, they also have 100+ home users, and that's where the issue comes in.

Apparently Cisco introduced a security "feature" where they create the session using a random high numbered port (e.g. 49123) but in the Via header, they say to respond to private IP, port 5060. So when the SBC sees the private address it assumes it is being NAT'd through a firewall and replies back to public IP, port 49123. What we're seeing is that the home router passes the response back to private IP, port 49123, which the phone doesn't accept (because it wants it on 5060) and the REGISTER fails.

As you know most home routers are poor at handling ALG (and we've tested and found they are equally bad at handling this scenario). We (and the customer) don't want to troubleshoot 100+ individual home routers.

We haven't found a way to turn off this really awesome "feature" so we're trying to find other solutions. Anyone been through this and have any suggestions?

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