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New Member

Unexpected routing behavior on 7609 router

Router novice here... 

We have a lab network set up with a 7609 router as the central core.  Scenario:  Laptop with a SIP client.  In the lab is a session border controller that will route signaling and media to a SIP gateway with a call agent (172.23.112.201) and a media "handler" (172.23.113.6).  The call processing device will forward packets to an RF network (108.x.x.x) where an NCS cable modem sits.

Call signaling works perfectly fine.  However, RTP traffic from the laptop to the NCS phone is getting routed incorrectly.  RTP traffic from the phone to the laptop works fine.

Expected traffic patterns:

Laptop to phone:  Orange + Blue in picture below.  Laptop > corporate router > 7609 > SBC > 7609 > SIP Gateway > 7609 > CMTS > MTA > Phone.

Phone to laptop:  Green in picture below.  Phone > MTA > CMTS > 7609 > SIP Gateway > 7609 > SBC > 7609 > corporate router > Laptop.

Packet captures show the laptop to phone RTP packets are being routed back towards the corporate router.  These time out with ICMP TTL exceeded packets.  There are static routes for 172.23.113.0/27 to the optical interfaces that go to the SIP gateway.  Interestingly, I can ping an IP on the SIP gateway (not used for media, but is pingable) in that static range (172.23.113.1) just fine from the 7609 (i.e. it's not getting routed to the corporate router).  Unfortunately, the IP for the media endpoint on the SIP gateway is not pingable.  Config for the 7609 is attached.

Any thoughts?  Questions I have concerning the config are with the "ip source-route" entry as well as the mls & cef entries.

One Way Audio.jpg

2 REPLIES
New Member

Unexpected routing behavior on 7609 router

Forgot to specify... the actual laptop to phone routing that is occurring is the orange + red lines in the image.

New Member

Unexpected routing behavior on 7609 router

Ok, figured out the issue.

The SBC is sending RTP to the mac of the corporate router, which does not route 172.23.113.x to the lab 7609 router.  It's a config issue on the SBC.

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