On 3/18/14, 12:41 AM, Matthew Seaman wrote:
On 18/03/2014 03:56, Ronald F. Guilmette wrote:
(It was explained to me at the time that NTP operates a bit like DNS...
with which I am more familiar... i.e. that all outbound requests originate
on high numbered ports, well and truly away from all low numbered ports,
including, in particular, 123. I am just re-verifying that my understanding
in this regard is correct, and that my current blanket firewall rule is
fine as it stands.)
It's not uncommon for NTP to have both source and destination ports set
to 123. This was the standard some years back, but such things as NAT
always meant that couldn't be relied on. I don't know if this is still
seen as a normal practice, but all the NTP related entries sockstat
shows me are bound to port 123 on the local side.
Unlike DNS, I don't think there are any particular security penalties to
not using a wide range of UDP source ports for NTP.
yes, you are correct.. in fact what I have is a rule that only allows
ANY udp packets if they are responses to something I sent.
I have an exception rule for DNS which I do serve.
I have an option in my firewall that further narrows that down to only
allow ME to send udp (other than dns) packets to my own ntp sources.
so even if my
ntpd were somehow comromised it couldnt reach anyone else.
Cheers,
Matthew
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