How do I open UDP port 123 thru the Cisco 1941 router

Posted on 2011-03-09
Last Modified: 2012-05-11
I am new in cisco, and I have one question about open UDP port 123. I have a 1941 router. I need to open UDP port 123 for to one of my internal server (IP Do I use the following? Thank you in advance.

permit udp eq 123
Question by:weikiiro
  • 3

Expert Comment

ID: 35088682
Correct ,But you also need to assign this access-list to an interface.
And also you have decide in which direction it has to assign.

As an example if your is in the range for fast ethernet 0/1 and your Server is in the range of Fast ethernet 0/0 then :

Conf t
ip access-list extended Test
Interface fa0/1
access-group Test in


Thats all.

Expert Comment

ID: 35088714
Sorry i have to correct my previous syntax :

Ip access-group Test in

Author Comment

ID: 35088931
ic, thank you for your help mrmozaffari. for permit udp eq 123, should the external Ip go first or internal ip? I need to establish a 2 way communication.

Accepted Solution

mrmozaffari earned 500 total points
ID: 35089050
You did it correctly ,Why ?
Oh just one :
To define a correct access list ; Your syntax is not correct,
Don't Forget Wild card or "Host"
Correct is :

permit udp eq 123


permit udp Host Host eq 123

They are same.

It is the structure of the Extended ACLs :

Permit/Deny Protocol [Source] [Destination]
for permit Rule :

Permit [protocol] [Source address] [Wild card mask] [eq] [port number] [Destination Address] [Wild card mask] [eq] [port number]

Best Regards,

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