ipf icmp types?

[Seth Arnold <sarnold_(_at_)_willamette_(_dot_)_edu>]

Greetings,

once in a while, every few minutes I think, ipf puts something
similar to these entries into my logs:

Nov 30 00:16:53 sarnold ipmon[26825]: 00:16:52.616440              xl1 @0:11 b 172.144.210.58 -> 24.20.70.203 PR icmp len 20 28 icmp 8/0 IN 
Nov 30 00:16:59 sarnold ipmon[26825]: 00:16:58.935545              xl1 @0:11 b 24.5.253.142 -> 24.20.70.203 PR icmp len 20 32 icmp 8/0 IN 
Nov 30 00:17:25 sarnold ipmon[26825]: 00:17:25.092178              xl1 @0:11 b 172.155.122.95 -> 24.20.70.203 PR icmp len 20 28 icmp 8/0 IN 

RFC 792 suggests ICMP 8/0 is an echo reply. This I suppose is all well
and good, but why on earth are these machines replying? It isn't often I
send pings out -- certainly not this often. Once every few weeks is more
like it. :)

Any suggestions what this means?

Thanks :)

-- 
``Oh Lord; Ooh you are so big; So absolutely huge; Gosh we're all
really impressed down here, I can tell you.''