North American Network Operators Group

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traffic filtering

  • From: Stephen Griffin
  • Date: Mon Jan 21 17:55:51 2002


I'm curious about how many networks completely filter all traffic to
any ip address ending in either ".0" or ".255".

I'm curious because any network /0-/23,/31,/32 can legitimately have
ip addresses in-use which end as such. /32's can obviously have (most) any ip
address, since there is no notion of a network or broadcast address. /31
doesn't have a directed broadcast. For /0-/23 only the first ".0" and the
last ".255" correspond to reserved addresses. All of the intervening
addresses are legal.

Is this type of filtering common? What alternate solutions are available
to mitigate (I'm assuming) concerns about smurf amplifiers, that still
allow traffic to/from legitimate addresses. What rationale is used to
filter all traffic to network/broadcast addresses of /24 networks while
ignoring network/broadcast of /25-/30? For that matter, what percentage
of smurf amplifiers land on /24 boundaries?