diff --git a/docs/FAQ.xml b/docs/FAQ.xml index c94954f38..c37ed4948 100644 --- a/docs/FAQ.xml +++ b/docs/FAQ.xml @@ -1344,22 +1344,28 @@ DROP net fw udp 10619 Nov 25 18:58:52 linux kernel: Shorewall:net2all:DROP:IN=eth1 OUT= MAC=00:60:1d:f0:a6:f9:00:60:1d:f6:35:50:08:00 SRC=206.124.146.179 - DST=192.0.2.3 LEN=56 TOS=0x00 PREC=0x00 TTL=110 ID=18558 PROTO=ICMP - TYPE=3 CODE=3 [SRC=192.0.2.3 DST=172.16.1.10 LEN=128 TOS=0x00 PREC=0x00 + DST=192.0.2.3 LEN=56 TOS=0x00 PREC=0x00 TTL=110 ID=18558 PROTO=ICMP + TYPE=3 CODE=3 [SRC=192.0.2.3 DST=172.16.1.10 LEN=128 TOS=0x00 PREC=0x00 TTL=47 ID=0 DF PROTO=UDP SPT=53 DPT=2857 LEN=108 ] 192.0.2.3 is external on my firewall... 172.16.0.0/24 is my internal LAN - Answer: While most people - associate the Internet Control Message Protocol (ICMP) with - ping, ICMP is a key piece of IP. ICMP is used to report - problems back to the sender of a packet; this is what is happening here. - Unfortunately, where NAT is involved (including SNAT, DNAT and - Masquerade), there are a lot of broken implementations. That is what you - are seeing with these messages. When Netfilter displays these messages, - the part before the "[" describes the ICMP packet and the part between - the "[" and "]" describes the packet for which the ICMP is a + Answer: First of all, please note + that the above is a very specific type of log message dealing with ICMP + port unreachable packets. Do not read this answer and assume that all + Shorewall log messages have something to do with ICMP (hint -- see FAQ 17). + + While most people associate the Internet Control Message Protocol + (ICMP) with ping, ICMP is a key piece of IP. ICMP is used + to report problems back to the sender of a packet; this is what is + happening here. Unfortunately, where NAT is involved (including SNAT, + DNAT and Masquerade), there are a lot of broken implementations. That is + what you are seeing with these messages. When Netfilter displays these + messages, the part before the "[" describes the ICMP packet and the part + between the "[" and "]" describes the packet for which the ICMP is a response. Here is my interpretation of what is happening -- to confirm this