AT&T blocking port 123

Hal Murray halmurray at
Fri Aug 5 20:09:54 UTC 2022

Does anybody have an AT&T residential account?

Google gets lots of hits on the subject.

Their forums have several comments similar to this one:
> No, Port 123 is restricted both ways on residential AT&T accounts because
> it's a known DDoS risk.

With no help at all for how to get time.

That links to:
Down at the bottom is a table of the ports they block which says they block 
port 123 in both directions.

>From another thread:

> AT&T performs source port blocking for port 123 for traffic coming from
> endpoints in its network.  It allows requests to go to servers on port 123.
> NTP peers use both a source and a destination port of 123, so this would
> typically block traffic.
[But if you go through NAT, the internal source port gets translated so it 

I'm a bit surprised I haven't heard about this before.  Is this well known and 
I just, somehow, missed it?

These are my opinions.  I hate spam.

More information about the devel mailing list