NTP & NAT

[volkovstanislav]

Hi,

somebody please explain , why cisco router when perform PAT choose source ports from reserved IANA range.

Example:

2801_Stend#sh ip nat translations | inc :123|Pro

Pro Inside global Inside local Outside local Outside global

udp xxx.xxx.xxx.130:5 172.16.17.2:123 67.215.65.132:123 67.215.65.132:123

udp xxx.xxx.xxx.130:6 172.16.17.2:123 78.46.194.186:123 78.46.194.186:123

udp xxx.xxx.xxx.130:7 172.16.17.2:123 88.198.34.114:123 88.198.34.114:123

udp xxx.xxx.xxx.130:9 192.168.214.24:123 84.204.87.243:123 84.204.87.243:123

udp xxx.xxx.xxx.130:12 192.168.219.5:123 80.90.180.140:123 80.90.180.140:123

udp xxx.xxx.xxx.130:2 192.168.219.5:123 193.125.143.173:123 193.125.143.173:123

udp xxx.xxx.xxx.130:16 192.168.220.50:123 195.13.1.153:123 195.13.1.153:123

udp xxx.xxx.xxx.130:1 192.168.220.50:123 213.142.207.7:123 213.142.207.7:123

udp xxx.xxx.xxx.130:14 192.168.220.58:123 91.189.94.4:123 91.189.94.4:123

udp xxx.xxx.xxx.130:11 192.168.220.117:123 84.204.87.243:123 84.204.87.243:123

udp xxx.xxx.xxx.130:8 192.168.220.117:123 195.13.1.153:123 195.13.1.153:123

udp xxx.xxx.xxx.130:23 192.168.220.250:123 62.141.95.246:123 62.141.95.246:123

udp xxx.xxx.xxx.130:123 192.168.220.251:123 62.141.95.246:123 62.141.95.246:123

udp xxx.xxx.xxx.130:10 192.168.231.236:123 211.233.40.78:123 211.233.40.78:123

udp xxx.xxx.xxx.130:512 192.168.231.240:512 208.53.158.34:123 208.53.158.34:123

udp xxx.xxx.xxx.130:15 192.168.235.70:123 216.144.229.211:123 216.144.229.211:123

2801_

Sent from Cisco Technical Support iPad App

[hobbe]

Hi

I am not sure about this

but it could be because UDP is normally connected to and from the same port number.

If you connect to a UDP 1234 then in most applications this will then come from port 1234.

so it could be to maintain a compability thing.

This is just my guess on the matter but it makes sense to me.

Good luck

HTH