[Pool] DDoS Type Attack

Mouse mouse at Rodents-Montreal.ORG
Fri Feb 14 13:35:47 UTC 2014

>> it seems any remote client who needs to talk to our NTP servers on
>> UDP 123, must also originate the request from UDP 123.

>> Could someone confirm if this is correct?  Or are we blocking
>> legitimate reqeusts as well?

> You are blocking legitimate requests as well.  One example: traffic
> coming from behind NAT firewalls. NAT changes the source port to some
> other port.

Opinions differ on how `legitimate' such traffic is.  My own stance is
that anyone doing NAT has earned any resulting brokenness by
deliberately corrupting packets in transit.

However, I don't think any spec calls for the use of port 123 on both
ends of NTP traffic, so even if you agree with my stance I see no
reason to think all non-123/123 traffic is due to NAT.  That is, at
best you're using a heuristic that mostly works - no worse than any
other heuristic, but no better, either, really.

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