[Snort-users] Is this a valid traffic?
joem at ...692...
Wed Apr 3 11:13:29 EST 2002
At 12:39 PM 4/3/02, Skip Carter wrote:
> -- the packet size is 1500 bytes. There is never any reason for an
> to be larger than 128 bytes.
I see these all the time and have commented this rule out. This looks like
the MTU discovery that comes with some of the newer *nix versions. A ping
packet is sent out with
a "don't fragment" bit set, 1500 bytes in size, and if a remote
router can't forward the packet on a smaller MTU channel (say some
old serial link), it will return a "can't fragment" ICMP pkt.
to the web server, which will then lower the packet size for
that host. In today's internet, those who can't handle
a 1500 byte packet should be < .1%, so all that traffic is extraneous.
One of our groups shut this off in their AIX web server a year ago because
folks were complaining that they were getting ping scanned from it. They
upgraded the OS on Monday and guess what -- it was turned back on by the
upgrade. They shut it back off. I've also seen this behavior in Solaris
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