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author | cjc <cjc@FreeBSD.org> | 2002-05-01 06:29:16 +0000 |
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committer | cjc <cjc@FreeBSD.org> | 2002-05-01 06:29:16 +0000 |
commit | 6b0c9026c6322f63603f8716a3da2bcf9ca230b6 (patch) | |
tree | 57c6a5e5a59c5e67d936cafb4d00efbc59d40f9e /sbin/ipfw/ipfw.8 | |
parent | 7b6f84310a6bb3411a131c01ba2e7b01e558752c (diff) | |
download | FreeBSD-src-6b0c9026c6322f63603f8716a3da2bcf9ca230b6.zip FreeBSD-src-6b0c9026c6322f63603f8716a3da2bcf9ca230b6.tar.gz |
Enlighten those who read the FINE POINTS of the documentation a bit
more on how ipfw(8) deals with tiny fragments. While we're at it, add
a quick log message to even let people know we dropped a packet. (Note
that the second FINE POINT is somewhat redundant given the first, but
since the code is there, leave the docs for it.)
MFC after: 1 day
Diffstat (limited to 'sbin/ipfw/ipfw.8')
-rw-r--r-- | sbin/ipfw/ipfw.8 | 17 |
1 files changed, 14 insertions, 3 deletions
diff --git a/sbin/ipfw/ipfw.8 b/sbin/ipfw/ipfw.8 index 6966a74..aaaf9dc 100644 --- a/sbin/ipfw/ipfw.8 +++ b/sbin/ipfw/ipfw.8 @@ -1052,9 +1052,20 @@ Don't forget the loopback interface. .Sh FINE POINTS .Bl -bullet .It -There is one kind of packet that the firewall will always -discard, that is a TCP packet's fragment with a fragment offset of -one. +There are circumstances where fragmented datagrams are unconditionally +dropped. +TCP packets are dropped if they do not contain at least 20 bytes of +TCP header, UDP packets are dropped if they do not contain a full 8 +byte UDP header, and ICMP packets are dropped if they do not contain +4 bytes of ICMP header, enough to specify the ICMP type, code, and +checksum. +These packets are simply logged as +.Dq pullup failed +since there may not be enough good data in the packet to produce a +meaningful log entry. +.It +Another type of packet is unconditionally dropped, a TCP packet with a +fragment offset of one. This is a valid packet, but it only has one use, to try to circumvent firewalls. When logging is enabled, these packets are |