Re: TWC (AS11351) blocking all NTP?

["Dobbins, Roland" <rdobbins () arbor net>]

On Feb 3, 2014, at 1:02 PM, Dobbins, Roland <rdobbins () arbor net> wrote:

> b) enforce their AUPs (most broadband operators prohibit operating servers) by blocking *inbound* UDP/123 traffic 
> towards their customers at the customer aggregation edge

Actually, this can cause problems for ntpds operating in symmetric mode, where both the source and destination ports 
are UDP/123.  Allowing inbound UDP/123 - UDP/123 and then rate-limiting it would be one approach; another would be to 
block outbound UDP/123 emanating from customers based upon packet size, if one's hardware allows matching on size in 
ACLs.

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Roland Dobbins <rdobbins () arbor net> // <http://www.arbornetworks.com>

          Luck is the residue of opportunity and design.

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