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NTP through ASA

I am trying to setup NTP from a router that is behind an ASA. I am trying to sync it with (UDP port 123). However, the "sh asso det" list the NIST server as "insane and invalid". The ASA does do a source NAT and also changes the source port. When I use my backup internet connection that is a DSL modem then NTP work fine, different NAT address. On the ASA, for NTP, the packets are getting NAT'ed and UDP session is built. After 2 minutes the session is tore down.

Here is the syslog message:

Built outbound UDP connection 186440 for ouside: ( to inside:

I have forced the NAT so that the source port stays 123 after NAT but no change.


Appreciate any input.

  • Firewalling
Hall of Fame Super Silver

NTP shouldn't care what your

NTP shouldn't care what your source port is, as long as the destination is udp/123.

Since it looks like the udp flow is being setup, I'd suspect something upstream isn't getting your packets to the destination NTP server.

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