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New Member

One-way SIP audio through Cisco SF300-48p and 2901.

Got another weird one that we are struggling to figure out. 

We have a voice only network with a Cisco 2901, a cisco SF300-48p is trunked to the router with 3 more SF300-24p starred off it.

All the 2901 is doing routing to the voice gateway from the remote location.

We have pulled many captures and not one has had an issue when listening to the calls using the RTP stream analysis.

Verified all mac addresses are indeed Cisco VoIP phones and verified that the ARP table is populated with the same macs.

So far we have been able to tell that no data is traversing this network, and it is indeed just voice traffic.

The main complaint we are having is one way audio coming from the voice gateway. Like stated before captures taken at the voice gateway and before the router all sound normal, we are unable to capture on the voice network due to resources.

I cannot find anything online showing other people having issues with the SF300-48pand voice, and most say that is teh best switch out there for small applications like ours.

I don't see any issues with link overload or any other bandwidth type issues on the links.

Any advice as to where to go next would be appreciated, I can tell you the config on the switches are pretty much defualt with the exception of the "Auto Voice VLAN" being set and enabled to 100. Other than that nothing else has been changed and the smartport settings are all defualt.

The router config is the most basic you will ever see, outside/inside interfaces with nat and "no ip nat service sip udp port 5060" applied since we have had issues with phones registering multiple times without that command.

I can post screenshots and show run, as I don't have access at this time.





  • LAN Switching and Routing

Hi,Most VoIP one way audio


Most VoIP one way audio issues are
IP routing caused ( A few times it can be phone sw loads etc)

Can you prove with ping etc that there
is good ip routing from the voice vlan to 
the voice gateway and vice versa ?

Is there a firewall in the route?
Are you allowing the rtp through in
both directions ?


Regards, Alex. Please rate useful posts.
New Member

Haven't tried a ping yet,

Haven't tried a ping yet, there is no firewall and I am certian that rtp is allowed as there are other remote locations that are working perfectly fine.  If a routing issue why would the wireshark captures sound fine?  They are captured right before the router.


I will popst the ping along with any need config tomorrow.

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