Question

Recommendation / steps  NTP access through Cisco ASA firewall

Asked by: markpalinux


I need to configure a Cisco ASA 8.0 to allow access to Internet NTP servers.
1)
the syntax of the rule to allow , NTP port 123 udp
2)
should I allow two or three servers access to use port 123 or specific servers, I am asking because I know the list will grow  /change over time  would it be a big security risk?
3) I have another site at ASA with version 7 ? same syntax?


Background:

Configuring a time source for the forest
http://technet.microsoft.com/en-us/library/cc784800(WS.10).aspx

In Active Directory the domain should synchronize clocks according to Active Directory hierarchy.   The PDC emulator ( AD FSMO role ) should be set to a Internet NTP  ( SNTP) server.  I know over time the PDC emulator will likely be transferred to another server.

NTP uses UDP port 123.


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Asked On
2009-10-06 at 18:42:52ID24791068
Topics

Enterprise Firewalls

,

Cisco PIX Firewall

Participating Experts
2
Points
500
Comments
3

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Answers

 

by: PeteLongPosted on 2009-10-07 at 04:24:08ID: 25514129

Configure the Servers as per my website here

http://www.petenetlive.com/Tech/Windows/EventID/Events/time_events.htm

Then on the firewall allow UDP Outbound

access-list outbound extended permit udp any any eq 123
access-group outbound in interface inside

NOTE this assumes you DO NOT have an access group applied to the inside interface - if you do change the word "outbound" to match the one on your firewall

I tend to open time for all clients but if you wanted to lock it down to just the PDC emulator then use the following instead (where 192.168.1.1 is the ip of the server in question).

access-list outbound extended permit udp host 192.168.1.1 any eq 123
access-group outbound in interface inside

 

 

by: rsivanandanPosted on 2009-10-19 at 07:59:48ID: 25605742

I would recommend only your DC's to get out of ASA and do the time sync.

All other domain computers can be configured to sync time from DC's. This would be scalable and remain simple, as you don't have to allow every PC on the network go out and sync.

It is not only a security issue but an efficiency matrix, like every machine downloading windows updates from microsoft site (think about the volume of that).

Now coming to the syntax, what Pete has above is basically to it, except for you add the machines which you want to allow to go out.

8.0 or 7.0 -> same syntax.

Cheers,
rsivanandan

 

by: PeteLongPosted on 2009-11-03 at 04:41:31ID: 25728316

Thanq

20120131-EE-VQP-002

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