In my firewall logs I see lots of entries like this.
IN= OUT=eth0 SRC=192.168.1.105 DST=18.104.22.168 LEN=148 TOS=0x00 PREC=0xC0 TTL=64 ID=55705 PROTO=ICMP TYPE=3 CODE=3 [SRC=22.214.171.124 DST=192.168.1.105 LEN=120 TOS=0x00 PREC=0x00 TTL=54 ID=0 DF PROTO=UDP SPT=53 DPT=25566 LEN=100 ]
It looks like the OpenDNS server at 126.96.36.199 sent my computer some kind of message by UDP from port 53, and my computer tries to respond with an ICMP code type 3 (which my firewall blocks, because I've configured it to block ICMP out, with a few exceptions.)
An ICMP type 3 coming from the OpenDNS servers would make sense, since my computer would try to query their servers, but I don't understand why my computer would try to send this message to their servers, unless their servers were trying to query my own computer for some destination, and I don't understand why their servers would do that.
Is that UDP packet coming from their severs some kind of query?
What's going on here?