[Freeswitch-users] [SOS] Help Needed with Strange Behavior

[Moe Navid]

Hi Anthony,

Thank you very much for your response.

After almost 9 hours of debugging I was able to reproduce the issue.

I went through all our logs and found out whenever a particular customer
calls out, we loose connectivity with our router.

I found out the customer had moved his IP Phone from his office to another
location. That location has same private IP address as our servers.

On all our servers we use 10.0.0.0/24 on eth0 and eth1 has public IP
address.

What I did next was isolated a FreeSWITCH server and spawn up a dedicated
Kamailio to only send traffic to this FS server. I also changed my lab's
LAN from 172.16.16.0/24 to 10.0.0.0/24.

Here is what happens when I make a call:

First call is fine and I get:

switch_rtp.c:5846 Auto Changing port from 10.0.0.179:61856 to
108.178.144.243:10249

On second call, here is what happens:

The value of rtp_session->flags[SWITCH_RTP_FLAG_AUTOADJ] is correctly set
to 1 but the “bytes" variable is always at zero for following if statement
on line 5833 in switch_rtp.c:

if (bytes && rtp_session->flags[SWITCH_RTP_FLAG_AUTOADJ] &&
switch_sockaddr_get_port(rtp_session->from_addr))

I also did raw packet captures on eth1, I found out right after my FS
receives SIP 183 with SDP from carrier, it sends out following:

1) an ICMP to my public IP address which is 108.178.144.243

2) an ARP broadcast “Who has 10.0.0.179? Tell 208.65.xxx.xxx”
(208.65.xxx.xxx is the public IP of the FS server)

Right after that, the router is no longer reachable and 10.0.0.179 will
show up in arp table of FS with mac address of the router.

I tested above scenario zillion times to make sure it’s reproducible before
reporting back.

What I did next was installing rtpproxy and made few changes to our
Kamailio to rewrite SDP and pass the traffic through rtpproxy and when I
make calls with rtpproxy in the middle, the problem does not occur.

Any thoughts?

Thank you,

Moe
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