Yes, if you use NAT, you cannot block fragmented packets.
Assuming my testing isn't too lame then you can drop with a policer. It will still let the last packet through though, as the match is on the more fragments flag. I suppose using the next field could do them all - but I don't know how to say not with u32.
tc qdisc add dev eth0 handle ffff: ingress
tc filter add dev eth0 parent ffff: prio 1 protocol ip u32 \ match ip protocol 17 0xff \ match u8 0x20 0x20 at 6 \ police rate 1kbit burst 10 drop \ flowid :1
The rate is irrelevant here, it's the burst 10 that means that only packets <= 10 bytes will ever pass.
To delete it do
tc qdisc del dev eth0 handle ffff: ingress
To see stats -
tc -s qdisc ls dev eth0
Andy.
PS
I had to remove jason from the cc as my isps mailserver threw a domain not found.
-----Original Message----- From: netfilter-bounces@xxxxxxxxxxxxxxxxxxx [mailto:netfilter-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Bruno Wallace Sent: Monday, January 03, 2005 7:39 AM To: Jason Opperisano; netfilter@xxxxxxxxxxxxxxxxxxx Subject: Re: how to block udp frag?
the iptables dont see this traffic..
On Sat, 1 Jan 2005 19:08:45 -0500, Jason Opperisano <opie@xxxxxxxxxxx> wrote:
On Sat, Jan 01, 2005 at 09:58:41PM -0200, Bruno Wallace wrote:
hello, how to block this?????
20:53:44.628586 83.102.166.15 > xxx.xxx.151.35: udp (frag 1720:25@512) (ttl 53, len 45) 0x0000 4500 002d 06b8 0040 3511 2599 5366 a60f E..-...@5.%.Sf.. 0x0010 c896 9723 11ef 0035 0019 1e70 71f7 0100 ...#...5...pq... 0x0020 0001 0000 0000 0000 0000 0200 0100 .............. 20:53:47.197264 83.102.166.24 > xxx.xxx.151.34: udp (frag 48577:25@512) (ttl 53, len 45) 0x0000 4500 002d bdc1 0040 3511 6e87 5366 a618 E..-...@xxxxxxxx 0x0010 c896 9722 11ef 0035 0019 1e68 71f7 0100 ..."...5...hq... 0x0020 0001 0000 0000 0000 0000 0200 0100 .............. 20:53:49.306206 83.102.166.76 > xxx.xxx.145.115: udp (frag 21990:25@512) (ttl 53, len 45) 0x0000 4500 002d 55e6 0040 3511 dbdd 5366 a64c E..-U..@xxxxxxxx 0x0010 c896 9173 11ef 0035 0019 23e3 71f7 0100 ...s...5..#.q... 0x0020 0001 0000 0000 0000 0000 0200 0100 .............. 20:53:49.529603 83.102.166.7 > xxx.xxx.146.119: udp (frag 26427:25@512) (ttl 53, len 45) 0x0000 4500 002d 673b 0040 3511 c9c9 5366 a607 E..-g;.@xxxxxxxx 0x0010 c896 9277 11ef 0035 0019 2324 71f7 0100 ...w...5..#$q... 0x0020 0001 0000 0000 0000 0000 0200 0100
thanks Bruno Wallace
either (a) use a default deny policy that doesn't allow UDP traffic or (b) in your rules where you accept UDP traffic, specify "! -f" which, according to the man page:
When the "!" argument precedes the "-f" flag, the rule will only match head fragments, or unfragmented packets.
-j
