[c-nsp] Issues with 2921, NAT and Skype?

Chuck Church chuckchurch at gmail.com
Thu Jun 11 13:46:04 EDT 2015

Not really positive, but Skype does rely on SIP I believe.  If so, the IOS
NAT could be trying to modify the addresses in the payload, which the
NAT-awareness in Skype itself is probably trying to correct.  Leading to a
lot of confused packets.  Try adding this:

no ip nat service sip tcp port 5060
no ip nat service sip udp port 5060

If not that, maybe it's a NAT timeout issue, maybe bump up the NAT timers.


-----Original Message-----
From: cisco-nsp [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of
Scott Granados
Sent: Thursday, June 11, 2015 12:53 PM
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] Issues with 2921, NAT and Skype?


I have a strange problem and I'm not familiar with the inner workings of
Skype to know for sure but I believe I have a problem caused by my NAT
config.  In some instances, after 1 minute the video will freeze especially
when using a Skype gateway to another service.  Point to point Skype calls
for the most part work and audio is generally unimpacted.  I have a very
basic NAT setup which follows.

interface GigabitEthernet0/1
 bandwidth 50000
 ip address
 ip access-group 101 in
 ip nat outside
 ip virtual-reassembly in
 media-type sfp
interface GigabitEthernet4/0
 ip address
 ip access-group 102 in
 ip nat inside
 ip virtual-reassembly in
ip nat inside source list 120 interface GigabitEthernet4/0 overload

Is there a modification to this that might better supports the needs of
Skype callers originating requests from behind this router?  Any pointers
that might have some general best practices for this type of setup?  Any
ideas would be most appreciated.

Thank you

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