What I need is help developing my troubleshooting process so I can figure this out on my own from now on. I want to learn how to fish rather than have someone hand me one, so to speak. Still, any insights at all would be helpful. ;-)

Environment:

Ubuntu
WAN: eth0
LAN: eth1 which is connected to a switch via a cross-over cable.
Currently all other machines are plugged into the switch.

Problem: I've a Vista Notebook that I'm trying to share my connection with. I've got DNS which is to say that I can ping the gateway box by it's dns name but no apparent connection besides.

I'm a Software developer but this is my first time with iptables. Seems like a great tool. Would really like to get to know how to use it. I've been operating out of a book so far but it doesn't provide much context for debug output.

Debug output:

jim@obsidian:~$ sudo /etc/init.d/firewall
jim@obsidian:~$ sudo iptables -t filter -L -v -n --line-numbers
Chain INPUT (policy DROP 0 packets, 0 bytes)
num pkts bytes target prot opt in out source destination
1 0 0 ACCEPT all -- lo * 0.0.0.0/0 0.0.0.0/0
2 0 0 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp spts:1024:65535 dpt:22 state NEW
3 0 0 ACCEPT udp -- * * 0.0.0.0/0 0.0.0.0/0 udp spts:1023:65534 dpt:53 state NEW
4 0 0 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp spts:1023:65534 dpt:53 state NEW
5 0 0 ACCEPT all -- * * 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED
6 0 0 ACCEPT icmp -- * * 0.0.0.0/0 0.0.0.0/0 icmp type 8
7 0 0 ACCEPT icmp -- * * 0.0.0.0/0 0.0.0.0/0 icmp type 11
8 0 0 ACCEPT icmp -- * * 0.0.0.0/0 0.0.0.0/0 icmp type 3
9 0 0 LOG all -- * * 0.0.0.0/0 0.0.0.0/0 limit: avg 15/min burst 5 LOG flags 0 level 7 prefix `INPUT - Dropped : '
10 0 0 DROP tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp flags:0x17/0x02

Chain FORWARD (policy DROP 0 packets, 0 bytes)
num pkts bytes target prot opt in out source destination
1 0 0 ACCEPT all -- eth1 eth0 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED
2 0 0 ACCEPT all -- eth0 eth1 0.0.0.0/0 0.0.0.0/0 state NEW,RELATED,ESTABLISHED
3 0 0 LOG all -- * * 0.0.0.0/0 0.0.0.0/0 limit: avg 15/min burst 5 LOG flags 0 level 7 prefix `FORWARD - Dropped : '

Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
num pkts bytes target prot opt in out source destination
1 0 0 LOG all -- * * 0.0.0.0/0 0.0.0.0/0 limit: avg 15/min burst 5 LOG flags 0 level 7 prefix `OUTPUT - Dropped : '

I've also got some log output:

jim@obsidian:/var/log$ tail -f kern.log | grep -v ": link"
Nov 8 01:03:02 obsidian kernel: [85621.452070] OUTPUT - Dropped : IN= OUT=eth0 SRC=66.235.54.84 DST=74.125.15.29 LEN=52 TOS=0x00 PREC=0x00 TTL=64 ID=56326 DF PROTO=TCP SPT=45843 DPT=80 WINDOW=66 RES=0x00 ACK URGP=0
Nov 8 01:03:15 obsidian kernel: [85634.879989] OUTPUT - Dropped : IN= OUT=eth0 SRC=66.235.54.84 DST=74.125.15.29 LEN=52 TOS=0x00 PREC=0x00 TTL=64 ID=56327 DF PROTO=TCP SPT=45843 DPT=80 WINDOW=66 RES=0x00 ACK FIN URGP=0
Nov 8 01:03:39 obsidian kernel: [85659.372389] INPUT - Dropped : IN=eth0 OUT= MAC=ff:ff:ff:ff:ff:ff:00:50:57:01:f3:75:08:00 SRC=66.235.36.1 DST=255.255.255.255 LEN=328 TOS=0x06 PREC=0x00 TTL=16 ID=0 PROTO=UDP SPT=67 DPT=68 LEN=308
Nov 8 01:03:46 obsidian kernel: [85665.628673] martian destination 0.0.0.0 from 10.10.58.1, dev eth0
Nov 8 01:03:47 obsidian kernel: [85666.629912] martian destination 0.0.0.0 from 10.10.58.1, dev eth0
Nov 8 01:03:48 obsidian kernel: [85667.625743] martian destination 0.0.0.0 from 10.10.58.1, dev eth0
Nov 8 01:05:02 obsidian kernel: [85742.400643] INPUT - Dropped : IN=eth1 OUT= MAC=ff:ff:ff:ff:ff:ff:00:16:d4:f8:99:b3:08:00 SRC=10.0.0.10 DST=10.0.0.255 LEN=99 TOS=0x00 PREC=0x00 TTL=128 ID=2398 PROTO=UDP SPT=64640 DPT=5353 LEN=79
Nov 8 01:05:05 obsidian kernel: [85744.402812] FORWARD - Dropped : IN=eth1 OUT=eth0 SRC=10.0.0.10 DST=192.168.0.198 LEN=83 TOS=0x00 PREC=0x00 TTL=127 ID=2399 PROTO=UDP SPT=39025 DPT=9100 LEN=63
Nov 8 01:05:40 obsidian kernel: [85780.368615] OUTPUT - Dropped : IN= OUT=eth0 SRC=66.235.54.84 DST=66.235.59.6 LEN=74 TOS=0x00 PREC=0x00 TTL=64 ID=0 DF PROTO=UDP SPT=9391 DPT=53 LEN=54
Nov 8 01:05:40 obsidian kernel: [85780.372695] OUTPUT - Dropped : IN= OUT=eth0 SRC=66.235.54.84 DST=66.235.59.6 LEN=69 TOS=0x00 PREC=0x00 TTL=64 ID=0 DF PROTO=UDP SPT=31328 DPT=53 LEN=49
Nov 8 01:05:40 obsidian kernel: [85780.376675] OUTPUT - Dropped : IN= OUT=eth0 SRC=66.235.54.84 DST=66.235.59.6 LEN=69 TOS=0x00 PREC=0x00 TTL=64 ID=0 DF PROTO=UDP SPT=29937 DPT=53 LEN=49
Nov 8 01:05:40 obsidian kernel: [85780.380408] OUTPUT - Dropped : IN= OUT=eth0 SRC=66.235.54.84 DST=66.235.59.6 LEN=69 TOS=0x00 PREC=0x00 TTL=64 ID=0 DF PROTO=UDP SPT=15637 DPT=53 LEN=49
Nov 8 01:05:40 obsidian kernel: [85780.384055] OUTPUT - Dropped : IN= OUT=eth0 SRC=66.235.54.84 DST=66.235.59.6 LEN=69 TOS=0x00 PREC=0x00 TTL=64 ID=0 DF PROTO=UDP SPT=24154 DPT=53 LEN=49
Nov 8 01:05:41 obsidian kernel: [85780.992630] INPUT - Dropped : IN=eth1 OUT= MAC=ff:ff:ff:ff:ff:ff:00:16:d4:f8:99:b3:08:00 SRC=10.0.0.10 DST=10.0.0.255 LEN=78 TOS=0x00 PREC=0x00 TTL=128 ID=2404 PROTO=UDP SPT=137 DPT=137 LEN=58
Nov 8 01:05:42 obsidian kernel: [85781.742153] INPUT - Dropped : IN=eth1 OUT= MAC=ff:ff:ff:ff:ff:ff:00:16:d4:f8:99:b3:08:00 SRC=10.0.0.10 DST=10.0.0.255 LEN=78 TOS=0x00 PREC=0x00 TTL=128 ID=2405 PROTO=UDP SPT=137 DPT=137 LEN=58
Nov 8 01:05:43 obsidian kernel: [85782.492236] INPUT - Dropped : IN=eth1 OUT= MAC=ff:ff:ff:ff:ff:ff:00:16:d4:f8:99:b3:08:00 SRC=10.0.0.10 DST=10.0.0.255 LEN=78 TOS=0x00 PREC=0x00 TTL=128 ID=2406 PROTO=UDP SPT=137 DPT=137 LEN=58
Nov 8 01:05:43 obsidian kernel: [85783.315852] FORWARD - Dropped : IN=eth1 OUT=eth0 SRC=10.0.0.10 DST=65.55.12.249 LEN=52 TOS=0x00 PREC=0x00 TTL=127 ID=2408 DF PROTO=TCP SPT=50102 DPT=80 WINDOW=8192 RES=0x00 SYN URGP=0
Nov 8 01:05:46 obsidian kernel: [85786.307624] FORWARD - Dropped : IN=eth1 OUT=eth0 SRC=10.0.0.10 DST=65.55.12.249 LEN=52 TOS=0x00 PREC=0x00 TTL=127 ID=2409 DF PROTO=TCP SPT=50102 DPT=80 WINDOW=8192 RES=0x00 SYN URGP=0
Nov 8 01:05:48 obsidian kernel: [85788.398340] FORWARD - Dropped : IN=eth1 OUT=eth0 SRC=10.0.0.10 DST=192.168.0.198 LEN=83 TOS=0x00 PREC=0x00 TTL=127 ID=2410 PROTO=UDP SPT=39025 DPT=9100 LEN=63
Nov 8 01:05:52 obsidian kernel: [85792.309332] FORWARD - Dropped : IN=eth1 OUT=eth0 SRC=10.0.0.10 DST=65.55.12.249 LEN=48 TOS=0x00 PREC=0x00 TTL=127 ID=2411 DF PROTO=TCP SPT=50102 DPT=80 WINDOW=8192 RES=0x00 SYN URGP=0
Nov 8 01:05:53 obsidian kernel: [85792.404265] INPUT - Dropped : IN=eth1 OUT= MAC=ff:ff:ff:ff:ff:ff:00:16:d4:f8:99:b3:08:00 SRC=10.0.0.10 DST=10.0.0.255 LEN=99 TOS=0x00 PREC=0x00 TTL=128 ID=2412 PROTO=UDP SPT=65048 DPT=5353 LEN=79
Nov 8 01:05:54 obsidian kernel: [85794.324617] OUTPUT - Dropped : IN= OUT=eth1 SRC=10.0.0.1 DST=10.0.0.10 LEN=276 TOS=0x00 PREC=0x00 TTL=64 ID=0 DF PROTO=UDP SPT=53 DPT=52740 LEN=256
Nov 8 01:05:54 obsidian kernel: [85794.334896] INPUT - Dropped : IN=eth1 OUT= MAC=ff:ff:ff:ff:ff:ff:00:16:d4:f8:99:b3:08:00 SRC=10.0.0.10 DST=10.0.0.255 LEN=78 TOS=0x00 PREC=0x00 TTL=128 ID=2414 PROTO=UDP SPT=137 DPT=137 LEN=58
Nov 8 01:05:55 obsidian kernel: [85794.407354] FORWARD - Dropped : IN=eth1 OUT=eth0 SRC=10.0.0.10 DST=192.168.0.198 LEN=83 TOS=0x00 PREC=0x00 TTL=127 ID=2415 PROTO=UDP SPT=39025 DPT=9100 LEN=63
Nov 8 01:05:55 obsidian kernel: [85795.084739] INPUT - Dropped : IN=eth1 OUT= MAC=ff:ff:ff:ff:ff:ff:00:16:d4:f8:99:b3:08:00 SRC=10.0.0.10 DST=10.0.0.255 LEN=78 TOS=0x00 PREC=0x00 TTL=128 ID=2416 PROTO=UDP SPT=137 DPT=137 LEN=58
Nov 8 01:05:56 obsidian kernel: [85795.834817] INPUT - Dropped : IN=eth1 OUT= MAC=ff:ff:ff:ff:ff:ff:00:16:d4:f8:99:b3:08:00 SRC=10.0.0.10 DST=10.0.0.255 LEN=78 TOS=0x00 PREC=0x00 TTL=128 ID=2417 PROTO=UDP SPT=137 DPT=137 LEN=58
Nov 8 01:05:57 obsidian kernel: [85796.587095] FORWARD - Dropped : IN=eth1 OUT=eth0 SRC=10.0.0.10 DST=65.55.12.249 LEN=52 TOS=0x00 PREC=0x00 TTL=127 ID=2418 DF PROTO=TCP SPT=50104 DPT=80 WINDOW=8192 RES=0x00 SYN URGP=0
Nov 8 01:05:59 obsidian kernel: [85798.411454] FORWARD - Dropped : IN=eth1 OUT=eth0 SRC=10.0.0.10 DST=192.168.0.198 LEN=83 TOS=0x00 PREC=0x00 TTL=127 ID=2419 PROTO=UDP SPT=39025 DPT=9100 LEN=63
Nov 8 01:05:59 obsidian kernel: [85798.466254] INPUT - Dropped : IN=eth0 OUT= MAC=00:14:c1:4b:df:64:00:50:57:01:f3:75:08:00 SRC=202.97.238.231 DST=66.235.54.84 LEN=598 TOS=0x00 PREC=0x00 TTL=52 ID=0 DF PROTO=UDP SPT=47980 DPT=1026 LEN=578
Nov 8 01:06:00 obsidian kernel: [85799.581197] FORWARD - Dropped : IN=eth1 OUT=eth0 SRC=10.0.0.10 DST=65.55.12.249 LEN=52 TOS=0x00 PREC=0x00 TTL=127 ID=2420 DF PROTO=TCP SPT=50104 DPT=80 WINDOW=8192 RES=0x00 SYN URGP=0
Nov 8 01:06:03 obsidian kernel: [85802.417404] INPUT - Dropped : IN=eth1 OUT= MAC=ff:ff:ff:ff:ff:ff:00:16:d4:f8:99:b3:08:00 SRC=10.0.0.10 DST=10.0.0.255 LEN=99 TOS=0x00 PREC=0x00 TTL=128 ID=2421 PROTO=UDP SPT=52744 DPT=5353 LEN=79
Nov 8 01:06:05 obsidian kernel: [85804.419856] FORWARD - Dropped : IN=eth1 OUT=eth0 SRC=10.0.0.10 DST=192.168.0.198 LEN=83 TOS=0x00 PREC=0x00 TTL=127 ID=2422 PROTO=UDP SPT=39025 DPT=9100 LEN=63
Nov 8 01:06:06 obsidian kernel: [85805.581912] FORWARD - Dropped : IN=eth1 OUT=eth0 SRC=10.0.0.10 DST=65.55.12.249 LEN=48 TOS=0x00 PREC=0x00 TTL=127 ID=2423 DF PROTO=TCP SPT=50104 DPT=80 WINDOW=8192 RES=0x00 SYN URGP=0
Nov 8 01:06:07 obsidian kernel: [85806.740181] OUTPUT - Dropped : IN= OUT=eth1 SRC=10.0.0.1 DST=10.0.0.10 LEN=276 TOS=0x00 PREC=0x00 TTL=64 ID=0 DF PROTO=UDP SPT=53 DPT=50882 LEN=256
Nov 8 01:06:07 obsidian kernel: [85806.751884] INPUT - Dropped : IN=eth1 OUT= MAC=ff:ff:ff:ff:ff:ff:00:16:d4:f8:99:b3:08:00 SRC=10.0.0.10 DST=10.0.0.255 LEN=78 TOS=0x00 PREC=0x00 TTL=128 ID=2425 PROTO=UDP SPT=137 DPT=137 LEN=58
Nov 8 01:06:08 obsidian kernel: [85807.501206] INPUT - Dropped : IN=eth1 OUT= MAC=ff:ff:ff:ff:ff:ff:00:16:d4:f8:99:b3:08:00 SRC=10.0.0.10 DST=10.0.0.255 LEN=78 TOS=0x00 PREC=0x00 TTL=128 ID=2426 PROTO=UDP SPT=137 DPT=137 LEN=58
Nov 8 01:06:09 obsidian kernel: [85809.003461] FORWARD - Dropped : IN=eth1 OUT=eth0 SRC=10.0.0.10 DST=65.55.12.249 LEN=52 TOS=0x00 PREC=0x00 TTL=127 ID=2428 DF PROTO=TCP SPT=50106 DPT=80 WINDOW=8192 RES=0x00 SYN URGP=0
Nov 8 01:06:12 obsidian kernel: [85811.994666] FORWARD - Dropped : IN=eth1 OUT=eth0 SRC=10.0.0.10 DST=65.55.12.249 LEN=52 TOS=0x00 PREC=0x00 TTL=127 ID=2429 DF PROTO=TCP SPT=50106 DPT=80 WINDOW=8192 RES=0x00 SYN URGP=0
Nov 8 01:06:18 obsidian kernel: [85817.996375] FORWARD - Dropped : IN=eth1 OUT=eth0 SRC=10.0.0.10 DST=65.55.12.249 LEN=48 TOS=0x00 PREC=0x00 TTL=127 ID=2430 DF PROTO=TCP SPT=50106 DPT=80 WINDOW=8192 RES=0x00 SYN URGP=0
Nov 8 01:06:22 obsidian kernel: [85822.006858] FORWARD - Dropped : IN=eth1 OUT=eth0 SRC=10.0.0.10 DST=65.55.12.249 LEN=52 TOS=0x00 PREC=0x00 TTL=127 ID=2432 DF PROTO=TCP SPT=50107 DPT=80 WINDOW=8192 RES=0x00 SYN URGP=0
Nov 8 01:06:28 obsidian kernel: [85828.008550] FORWARD - Dropped : IN=eth1 OUT=eth0 SRC=10.0.0.10 DST=65.55.12.249 LEN=48 TOS=0x00 PREC=0x00 TTL=127 ID=2433 DF PROTO=TCP SPT=50107 DPT=80 WINDOW=8192 RES=0x00 SYN URGP=0
Nov 8 01:06:40 obsidian kernel: [85840.055900] FORWARD - Dropped : IN=eth1 OUT=eth0 SRC=10.0.0.10 DST=65.55.12.249 LEN=60 TOS=0x00 PREC=0x00 TTL=127 ID=2434 PROTO=ICMP TYPE=8 CODE=0 ID=1 SEQ=57
Nov 8 01:06:44 obsidian kernel: [85843.626031] FORWARD - Dropped : IN=eth1 OUT=eth0 SRC=10.0.0.10 DST=65.55.12.249 LEN=60 TOS=0x00 PREC=0x00 TTL=127 ID=2435 PROTO=ICMP TYPE=8 CODE=0 ID=1 SEQ=58
Nov 8 01:06:48 obsidian kernel: [85847.626364] FORWARD - Dropped : IN=eth1 OUT=eth0 SRC=10.0.0.10 DST=65.55.12.249 LEN=60 TOS=0x00 PREC=0x00 TTL=127 ID=2436 PROTO=ICMP TYPE=8 CODE=0 ID=1 SEQ=59
Nov 8 01:06:48 obsidian kernel: [85847.829348] OUTPUT - Dropped : IN= OUT=eth1 SRC=10.0.0.1 DST=10.0.0.10 LEN=125 TOS=0x00 PREC=0x00 TTL=64 ID=0 DF PROTO=UDP SPT=53 DPT=59377 LEN=105
Nov 8 01:06:49 obsidian kernel: [85848.415168] FORWARD - Dropped : IN=eth1 OUT=eth0 SRC=10.0.0.10 DST=192.168.0.198 LEN=83 TOS=0x00 PREC=0x00 TTL=127 ID=2440 PROTO=UDP SPT=39025 DPT=9100 LEN=63
Nov 8 01:06:52 obsidian kernel: [85851.626810] FORWARD - Dropped : IN=eth1 OUT=eth0 SRC=10.0.0.10 DST=65.55.12.249 LEN=60 TOS=0x00 PREC=0x00 TTL=127 ID=2441 PROTO=ICMP TYPE=8 CODE=0 ID=1 SEQ=60
Nov 8 01:06:53 obsidian kernel: [85852.421089] INPUT - Dropped : IN=eth1 OUT= MAC=ff:ff:ff:ff:ff:ff:00:16:d4:f8:99:b3:08:00 SRC=10.0.0.10 DST=10.0.0.255 LEN=99 TOS=0x00 PREC=0x00 TTL=128 ID=2442 PROTO=UDP SPT=56174 DPT=5353 LEN=79
Nov 8 01:06:55 obsidian kernel: [85854.423512] FORWARD - Dropped : IN=eth1 OUT=eth0 SRC=10.0.0.10 DST=192.168.0.198 LEN=83 TOS=0x00 PREC=0x00 TTL=127 ID=2443 PROTO=UDP SPT=39025 DPT=9100 LEN=63

It looks to me like you've got your interfaces backwards in your rules, unless you made a mistake in your description. Also, you should probably let us look at your NAT table configuration too. You can do so by posting the output of:BTW, you're sure you've got IP forwarding enabled, right? You can check with:

Yep. Just figured out that the interfaces were bass ackwards in the script. This also explains why the debug output didn't make any sense to me. Still kicking myself. Still no network connectivity though. I have verified that DNS works without the firewall, BTW but I can see now in the logs where it is being blocked though. Going to try and poke a hole in the firewall to let it through.

Bingo! I added the ISP's DNS server to the list of DNS servers used on my Vista client's network interface and Viola! Instant access. As soon as I figure out how to put a hole in the firewall, it should work now. We'll see.

OK, I've got it working! :-)

Last thing I have to do is modify the ssh port for DOS and Brute force attacks on the external interface.