[cisco-voip] Cisco SIP Phones - Ephemeral Source Ports

[Boon]

Hi,

I ran into a peculiar issue last week where I had to advise a client on
firewall rules related to Cisco Phones running a SIP firmware image.

I was surprised to find that Cisco phones use an ephemeral source port
instead of 5060. Therefore for CUCM initiated SIP messages to phones the
destination port is from this ephemeral range.

Could somebody point me towards the documentation or release notes that
specify the use of this range of ports? Has it always been this way?

Unless I'm mistaken the CUCM TCP/IP Port Usage guide has always shown 5060
for CUCM-SIP Phone signalling.

Thanks
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