Filter NTP traffic by packet size?

Blake Hudson blake at
Tue Feb 25 20:09:38 UTC 2014

As an ISP in the USA, we try to follow the FCC's guidelines on a policy 
of non blocking. Not just because the FCC says so, but because we think 
it's in our and our customer's best interests. We don't dictate what our 
customer's can do with their internet connection as long as they're not 
breaking the law or negatively affecting the service for others.


Staudinger, Malcolm wrote the following on 2/25/2014 11:22 AM:
> Why wouldn't you just block chargen entirely? Is it actually still being used these days for anything legitimate?
> Malcolm Staudinger
> Information Security Analyst | EIS
> EarthLink
> E: mstaudinger at
> -----Original Message-----
> From: Blake Hudson [mailto:blake at]
> Sent: Tuesday, February 25, 2014 8:58 AM
> To: nanog at
> Subject: Re: Filter NTP traffic by packet size?
> I talked to one of our upstream IP transit providers and was able to negotiate individual policing levels on NTP, DNS, SNMP, and Chargen by UDP port within our aggregate policer. As mentioned, the legitimate traffic levels of these services are near 0. We gave each service many times the amount to satisfy subscribers, but not enough to overwhelm network links during an attack.
> --Blake

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