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[FYI] Broadcasts at NAPs

  • From: Lyndon Levesley
  • Date: Sat Aug 02 23:55:13 1997

This ICMP discussion reminded me that we've been logging broadcasts 
for a while at ME to see what percentage of traffic they represented 
and what it was (the wrong way round to track back thru ICMP DoS 

 If anyone's interested, the results are :      (254376 matches)     (1694830 matches)
any other dest.     (1047899270 matches)

which is 0.18% of the total accounted for by broadcasts. Bad, of 
course, but not as bad as I thought. I guess the bigger the provider 
the smaller percentage of total (that 1billion is total input on our 
FDDI since I applied the list, rather than total packets on the LAN)

 I'm assuming that a billion packets is enough to be a representative 

 A bit of a breakdown from the logs :

Split of broadcasts is 

	ICMP 12%
	UDP  88%

(actually, there were 5 packets for protocol 9 (private IGP?) but 
that's neither here nor there)

Port breakdown (based on a smaller sample to save resources)


I won't name names (I'll contact people later on probably) but 99.2% of 
the ICMP traffic comes from one provider (two routers) and is 
directed at That should be fairly easy to stop. Is 
there any good reason for a router to ping the broadcast address of a 


PORT: 53        PACKETS: 5
PORT: 67        PACKETS: 5364
PORT: 123       PACKETS: 9950
PORT: 161       PACKETS: 12
PORT: 513       PACKETS: 6635
PORT: 520       PACKETS: 19486
PORT: 5841      PACKETS: 4344

53 = DNS (badly configured cisco, but temporary so that's OK)
67 = BOOTPS (!) (probably misconfigured cisco again ;)
123 = NTP (ditto!)
161 = SNMP (?? - god knows why this would happen)
513 = who?
520 = routed ( oh dear)
5841 = ??? (is this CDP?)

 The upshot would seem to be that even with loads of misconfigured/
clueless stuff going on, random traffic is so insignificant that it 
wouldn't affect the performance of the NAP infrastructure.



Penis Envy is a total Phallusy.