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Long time reader here, first time poster. I usually find the answer to my problem thumbing through the threads. I ask far more questions than I answer, but here it goes.
I've got a Slackware box running as my gateway, router, firewall. My internal IP scheme is 10.10.10.x. I've got odd behavior that just appeared lately and it's bugging me something fierce. I've made no changes to my system lately, the machine's been untouched for about 90 days now. It just "works."
Here's what happens. I can talk to all my machines but one from the linux box (via ping), but ALL my machines, including the one I can't talk to, access the internet just fine through the linux box. The machine in question (from the logs pasted below) is 10.10.10.3. The machine I can't talk to gets "Destination Host Unreachable" from the gateway/linux box (10.10.10.1). This also prevents me from forwarding any ports to the 10.10.10.3 machine for the FTP server, bittorrent, remote desktop protocol.
Despite this, the host 10.10.10.3 access the internet just fine through the linux machine.
I've tried shutting the interfaces up and down, the routing table looks okay (it's listed below too), I've been at it for about 2 days on and off now and have had no resolution. Any help would be appreiciated greatly.
dave@atlantis:~$ ping 10.10.10.2
PING 10.10.10.2 (10.10.10.2) 56(84) bytes of data.
64 bytes from 10.10.10.2: icmp_seq=1 ttl=128 time=0.559 ms
64 bytes from 10.10.10.2: icmp_seq=2 ttl=128 time=0.399 ms
64 bytes from 10.10.10.2: icmp_seq=3 ttl=128 time=0.377 ms
--- 10.10.10.2 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 1998ms
rtt min/avg/max/mdev = 0.377/0.445/0.559/0.081 ms
dave@atlantis:~$ ping 10.10.10.3
PING 10.10.10.3 (10.10.10.3) 56(84) bytes of data.
From 10.10.10.1 icmp_seq=1 Destination Host Unreachable
From 10.10.10.1 icmp_seq=2 Destination Host Unreachable
From 10.10.10.1 icmp_seq=3 Destination Host Unreachable
--- 10.10.10.3 ping statistics ---
4 packets transmitted, 0 received, +3 errors, 100% packet loss, time 3000ms, pipe 3
dave@atlantis:~$ ping 10.10.10.100
PING 10.10.10.100 (10.10.10.100) 56(84) bytes of data.
64 bytes from 10.10.10.100: icmp_seq=1 ttl=64 time=0.914 ms
64 bytes from 10.10.10.100: icmp_seq=2 ttl=64 time=0.496 ms
64 bytes from 10.10.10.100: icmp_seq=3 ttl=64 time=0.492 ms
--- 10.10.10.100 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2010ms
rtt min/avg/max/mdev = 0.492/0.634/0.914/0.197 ms
well these machines are all local, so there is no routing going on, and no issue about your ethernet interfaces as you can reach the other machines. sounds to me like you simply have a firewall running on that particular device. when you ping it and it fails, check the arp cache on your client to see if it has been able to resolve that machine's mac address to the ip. "arp -n" i think... if it has a valid entry then there has to just be something on that machine dropping icmp packets.
I didn't think routing was an issue, because the proper 10.10.10.0 route is there and if that was boned, it would affect ALL the LAN machines.
There's no firewall running on the 10.10.10.3 machine. Windows Firewall is disabled and Norton's overly protective assault-any-packet-that-arrives Internet Security package was promptly disabled when I installed the anti-virus component.
Also, it's not just ping that doesn't work. It's everything. There's an FTP server running on that machine, and ftp claims "no route to host."
dave@atlantis:~$ ftp 10.10.10.3
ftp: connect: No route to host
Also, correct me if I am wrong. Wouldn't I just get a time out or refusal on the connection if it was a firewall issue? Not a "no route to host" or "destination host unreachable" error message? That's just my humble understanding of it. The target machine isn't actively refusing or timing out any requests, the linux machine just exclaims there's no route to it.
if the machine is rejecting packets then you would get a refusal, but if it is dropping packets instead then the machine may as well not exist at IP level. so this still certainly could be a firewall issue, but then if you are saying that it definitely is not, then we'll have to work with that assumption.
so you have all these other machines, can they talk to each other? can any other machine ping this invisible one?
Alright, the verdict is in, I'm a complete idiot. Apparently, at some point in the last few days, unknowing to me, this machine went from a static IP to a dynamic one. *sighs* Well, at least it was something simple. I discovered it when I tried to ping it by machine name from the other windows box and it came up with 10.10.10.246 (part of my dhcp pool).
Well, sorry I wasted everyone's time. I need to go do something to redeem myself. Thanks guys.