RTP: Specifying a Static Port

Unanswered Question
Oct 28th, 2007


As you know, RTP uses port range 16384 to 32767 dynamically. Can we define any specific static port manually so that rtp always use that udp port for voice call. I am using 3800 series router for voip setup. I tried to find any configuration but couldn't.

Waiting for immediate positive response…….

Best Regards


I have this problem too.
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Paolo Bevilacqua Sun, 10/28/2007 - 09:39

As far as I know, it is not possible to change that.

What problem are you trying to solve ?

rameezsardar Sun, 10/28/2007 - 11:00

My service provider says that he cann't assign priority to this long range rtp ports on its bandwidth manager. Are you sure, it is not possible? As i also could not found doc that mention commands regarding this.


Paolo Bevilacqua Sun, 10/28/2007 - 11:30

That is very strange because "bandwidth managers" should be very aware of RTP packets. Some can even recognize them without specify ports etc.

What you can do, is to have packets with DSCP EF given priority. That is the default for media packets with most equipment including cisco.

rameezsardar Sun, 10/28/2007 - 11:37

Actually Bandwidth Manager is a non-cisco device that manage bandwidth as well as prioritize traffic from specific ip or port over other traffic.

Paolo Bevilacqua Sun, 10/28/2007 - 12:28

Sure, all the ones I've seen allowed port ranges as well dscp settings. Is your isp familiar enough with the operation of the device ?

rameezsardar Sun, 10/28/2007 - 21:53

I think they are not much familiar with differentiated services because they just provide point to point links and have not big setup. Anyhow thanks and reconfirm whether commands for defining static ports are available or not.. Thanks for Responding...


Paolo Bevilacqua Mon, 10/29/2007 - 04:29

Not available as mentioned above. Please have your ISP familiarize with DSCP based QoS that is the worldwide standard.

rseiler Mon, 10/29/2007 - 09:08

NBAR can properly classify RTP and RTCP, so you could use NBAR on the outbound GigEthernet interface to remark the packets to a specific ToS/DSCP value that would match your service provider's contracted CoS value(s).

You do have multiple classes of service in your contract with your service provider?

You mentioned in an earlier post that this is a satellite link. Not for voice (UDP) traffic, but have you tried Cisco RBSP Satellite optimizations for TCP over the Satellite link?

vinay_verma80 Tue, 01/01/2008 - 22:14


U can not specify the rt static port as these will be negotiated at the time of call initiate

so their are 2 option for u is either user nbar or define policy map using the static ip address( eg loop back interface)



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