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One-way audio on calls placed across the PIX Firewall with NAT or PAT

Core Issue

This problem relates to voice communications across a toll-bypass network, as shown in this network configuration:

PSTN1---Gw1(192.168.210.30)-----inside(192.168.210.1)PIX(63.99.210.129)-Outside------Internet---------(66.196.208.253)GW2---PSTN2

When PSTN1 calls PSTN2 (or vice versa), PSTN1 can not hear PSTN2, but PSTN2 can hear PSTN1.

The PIX Firewall is doing Port Address Translation (PAT) for inside IP addresses with 63.99.210.130.

Issuing the show call active voice brief command on GW2(iad2420) reveals that the 63.99.210.130 is an H.323 peer, which is correct. Refer to this command output:

Telephony call-legs: 1

SIP call-legs: 0

H323 call-legs: 1

Total call-legs: 2

1290 : 2051562hs.1 +-1 pid:1 Answer 2146965151 connected

dur 00:00:00 tx:205/32482 rx:434/69440

Tele 1:23:125: tx:8690/869/0ms g711ulaw noise:0 acom:9  i/0:-50/-82 dBm

1290 : 2051563hs.1 +-1 pid:2 Originate 2148937404 connecting dur

00:00:00 tx:434/69440 rx:205/32482 IP 63.99.210.130:17300 rtt:12ms

pl:3410/20ms lost:0/1/0 delay:54/54/65ms

Issuing the show voip rtp connections command reveals that the remote RTP peer is 192.168.210.30. So the IP address of the inside gateway has not been translated. The GW2 is sending the Real-Time Protocol (RTP) stream to a private address that goes nowhere, as shown:

VoIP RTP active connections :

No. CallId  dstCallId  LocalRTP RmtRTP LocalIP         RemoteIP

1   120     119        16434    17850  66.196.208.253  192.168.210.30

The PIX allows traffic to pass correctly for H.225 but not H.245.

Resolution

For a workaround, add this on the inside gateway (GW1):

interface Loopback0
ip address 63.99.210.130 255.255.255.255
h323-gateway voip bind srcaddr 63.99.210.130

For more information, refer to the Bind the H.323 Signaling to a Specific IP Address on Cisco IOS Gateway/Routers section of Troubleshooting One Way Voice Issues.

Version history
Revision #:
1 of 1
Last update:
‎06-22-2009 03:40 PM
Updated by: