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Walkthrough Wednesdays

RTP port range


do I need to open the full UDP port range, 16384 - 32767 does CM and phones use every port in this range or could I reduce it to say the first 500 , does it look for the first open port?

whats the impact of reducing this?


The phone randomly selects a port from the range.

It's very dependant on the phone/app you use I think.

Some devs seem to pick a low port all the time, some pick different.

Save yourself a lot of pain, and open them all - better than spending all your time troubleshooting random failures...

Aaron Please remember to rate helpful posts to identify useful responses, and mark 'Answered' if appropriate!

I have modified the SIP profile for Jabber to use only 24 port instead of 32000 ports and I test was OK, my question there are any problem on reducing the RTP range?

Yes as you are limiting the number of concurrent calls. Unlike Expressway,
multiplexing can't be done naively by Jabber

Do you mean concurrent calls from same devise OR from all devices? And What do you mean by multiplexing can't be done naively by Jabber

>From all the devices. These ports will be allocated for all calls managed
Joseph Martini
Cisco Employee

Nipun Singh Raghav
Cisco Employee

You can open up the complete range on your firewall or if inspection is enabled then automatic udp pin holing does help as well.
Do remember that if you have ISR-4k, the UDP port range has been increased. 8000 - 48198 is the range supported by ISR-4k and also ASR routers.

Nipun Singh Raghav
"We cannot solve our problems with the same thinking we used when we created them"

I have similar question.


Voice Gateway ISR4xxx

-> RTP Ports 8000 to 48200


VoIp Provider, Patton Smartnode 5300

-> RTP Ports 6000 to 9999


The ports aren’t completly overlapping.

Does it work? Must be changed the port range on one side (Gateway or ISP) to get an 100% overlapping?

It should not matter. What your VoIP provider uses for RTP does not need to be part of what IOS supports. Example, let say your ISP want to receive RTP on port 6001. The router will just stream the RTP to that port. Similarly, if the IOS GW wants to receive RTP on port 41000, it will tell the ITSP in the SDP and it should just send the RTP stream to that port.

Nipun Singh Raghav
"We cannot solve our problems with the same thinking we used when we created them"

But if I have a firewall between the two devices (placed in different subnet). I must create a policy for RTP which one include the whole range:



- SIP = 5060

- RTP = 6000 to 48200


To GW:

- SIP = 5060

- RTP = 6000 to 48200


BR, Tifoso


checking to see if you got an answer to your last quesiton.

Yes, a firewall rule for the entire RTP range has to be created to ensure that packets to and from the SP are not dropped.

Hi guys 

quick question is it mandatory to open all RTP range ports from 16384 to 32766 from the firewall is there anyway to force telepresence end points to use lower range of ports than that??

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