Cause 127 Cisco VGW - Huawei VGW (H323)

Hello,

Last week, I helped two followers of my blog to solve a problem with an H323 connection between a Cisco Voice Gateway and a Huawei Voice Gateway. The topologies of both networks were as follows:

PBX1 (E1) -> E1 Cisco -> H323 -> Huawei E1 -> (E1) PBX2

The problem was this one: when an outgoing call was made from PBX1 to PBX2, the connection was not established, the caller received a hang-up. With a more detailed diagnosis, it was found that the Huawei gateway released the call.

Debug cch323 h225 was launched on the Cisco gateway to clarify the reason for the hang-up. He showed that Huawei was disconnecting the call with Cause 127:

Dec  3 08:22:13.748: //-1/cch323_h225_receiver: Received msg of type RELEASEIND_CHOSEN

Dec  3 08:22:13.748: //11760/release_ind: Disconnect cause 127 location code 0

Dec  3 08:22:13.748: //11760/cch323_h225_receiver: RELEASEIND_CHOSEN: src address = 10.22.255.33; dest address = 10.22.255.34

Cause 127 is usually set by the called party on incoming VoIP calls when the call comes from "unknown" or "untrusted" IP addresses. Many vendors (including Cisco on CUCM and on voice gateways with IOS rel.15.x) on their VoIP devices by default deny incoming calls from other VoIP devices if their IP address is not configured, or is not configured as "trusted ”, or is not specified as the IP address of the far-end side with which this system interacts. This is done intentionally to prevent the possibility of third-party calls at your expense (toll-fraud).

For Huawei routers, the allowed calling IP address is the one specified in the trunk group settings. Incoming calls from all other IPs will be released with Cause 127.

On Huawei, the trunk group setup looks like this (the settings and debugs are given for one of the two problematic networks):

#

 trunk-group h323 h323 symmetrical

  ...... (часть конфига пропущена)

  peer-address static 10.22.255.250 1720

That is, this Huawei gateway is waiting for a call from a device with an IP address of 10.22.255.250. Let's take a closer look at the previous debug:

Dec  3 08:22:13.748: //11760/cch323_h225_receiver: RELEASEIND_CHOSEN: src address = 10.22.255.33; dest address = 10.22.255.34

As you can see, the call to the Huawei gateway comes from the Cisco gateway, marked with a completely different IP address, and not the one expected by the Huawei gateway. Therefore, Huawei considers this address "untrusted" and hangs up the call. A more detailed examination of the problem revealed that on Huawei  they had configured the IP address of the Loopback interface of the Cisco gateway interface (10.22.255.250) as the address of the opposite side, and Cisco sent VoIP H323 packets with the address of its physical interface (10.22.255.33).

Solutions for this situation can be the following:

- reconfigure the peer-address on Huawei to the IP address of the physical interface of the Cisco gateway (i.e. in our example to 10.22.255.33)

- or force the Cisco Gateway to mark its VoIP packets for H323 signaling with the IP address of the Loopback interface:

interface Loopback0

  ip address 10.22.255.250 255.255.255.255

 h323-gateway voip bind srcaddr 10.22.255.250

Both readers who turned to me for help preferred the first option, i.e. they reconfigured their Huawei gateways.