source port offset for udp and tcp are both at 0 for IPv4
destination port offset for udp and tcp are both at 16 for IPv4
On 02/27/2010 11:46 AM, ratheesh k wrote:
port offset may be differ based on which layer 4 protocol , you are
using . If u dont specify protocol ( layer 4 ) , netfilter dont know
this .
Please find below some code sinppet from xt_multiport.c .
113 pptr = skb_header_pointer(skb, protoff, sizeof(_ports), _ports);
114 if (pptr == NULL) {
115 /* We've been asked to examine this packet, and we
116 * can't. Hence, no choice but to drop.
117 */
118 duprintf("xt_multiport: Dropping evil offset=0
tinygram.\n");
119 *hotdrop = 1;
120 return 0;
121 }
122
123 return ports_match(multiinfo->ports,
124 multiinfo->flags, multiinfo->count,
125 ntohs(pptr[0]), ntohs(pptr[1]));
thanks,
Ratheesh
On Sat, Feb 27, 2010 at 9:47 PM, U. George<netbeans@xxxxxxxxxxxx> wrote:
U'll have to let me know why "-p udp" is needed when the chain can only have
udp packets, and therefor can only process udp packets.
I dont want to test over (( and over ) and over ) again when I know that the
packet is already KNOWN to be from eth1 and of protocol UDP.
adding "-p UDP" to multiport does make iptables happy, but appears to be a
useless test.
On 02/27/2010 10:06 AM, ratheesh k wrote:
Port is in Layer 4 of protocol stack .
On Sat, Feb 27, 2010 at 8:33 PM, U. George<netbeans@xxxxxxxxxxxx> wrote:
In order to get to the chain, the protocol, as well as the interface must
match. PRE_UDP if already filtered for "-p udp" . So why does multiport
require another check for -p udp? Does it really need to have that option
in
order for it to work?
+ /sbin/iptables -t filter -N PRE_UDP
+ /sbin/iptables -t filter -A INPUT -i eth1 -p udp -j PRE_UDP
+ /sbin/iptables -t filter -A PRE_UDP -m multiport --dport
137,138,139,512,514,515,1433,1434 -j DROP
iptables v1.4.5: multiport needs `-p tcp', `-p udp', `-p udplite', `-p
sctp' or `-p dccp'
Try `iptables -h' or 'iptables --help' for more information.
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