Extremely Strange Network Issue

adastra · Tux's lil' helper Joined: 16 Oct 2002 Posts: 106

I have no idea why such a thing would happen . . .

Installed LiveCD 1.4rc1 two weeks ago and am very pleased. Love it.
Previously had Redhat 7.3 loved it too but a bit bulky.

I'm surfing around on mozilla and decide to check out the activity on a Debian box I maintain running Debian-SF (sourceforge). Can't connect with Mozilla. Try Konqueror. Can't connect. Try IE on my Microshaft box. Get right on.

Long story short, I CAN'T EVEN PING THIS BOX!! Ping resolves the name into an IP but just sits there. When I ctrl-C I get 100% packet loss. I can't ssh into this box, connect with telnet, connect with ftp, or connect with a web browser from my Gentoo. (my BSD and Redhat boxen connect just fine)

Say the IP of the Debian box in question is ##.##.57.119. . .
I can ping/connect/ssh ##.##.57.120 and ##.##.57.118. . . but not 119.

All other boxes (windows or *nix) can do anything to this ##.##.57.119 they want to but my Gentoo can't even ping it. All other websites from my Gentoo are accessible.

Any ideas would be greatly appreciated. I am really at a loss.
I have already checked for iptables and chains but neither are installed/running.

rac · Posted: Wed Oct 16, 2002 10:40 pm Post subject:

What kernel sources are you using? Does running tcpdump on both machines tell you anything?
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RagManX · Posted: Thu Oct 17, 2002 4:17 am Post subject:

Are you on the same network as the machine with which you can't communicate? Could be an ARP issue. But as rac said, running tcpdump on both machines is your best bet. What exactly is the destination machine seeing from you? What is it sending back? I suspect your traffic is getting there but it is somehow confused on who you are and not talking back to the correct machine.

RagManX
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adastra · Tux's lil' helper Joined: 16 Oct 2002 Posts: 106

I am running kernel 2.4.19. I chose the vanilla kernel during the install.

I have never used tcpdump but will look into its capabilities. However, here is why i don't think the Debian-SF machine can be confused about where to reply back to.

My Gentoo is a laptop and I use it in one of two places, home and at school. At home I have DSL and am behind a DSL router running DHCP with my M$, BSD and another Debian machine (not the Debian-SF machine I can't get to). My Gentoo can get to any of these machines behind the firewall as well as any other machines outside the firewall, just not the Debian box located at school. In addition, all these boxes behind the DSL router can reach the Debian-SF machine at school.

When I take the laptop to school I am behind a Smoothwall (linux) box running DHCP and ipmasq. From there it is more of the same (other boxes behind the firewall get to the Debian-SF box just fine but not my laptop).

When I had Redhat 7.3, I had no problems reaching the Debian-SF machine. I have not changed any hardware since then. I always receive the same IP from the DHCP firewalls at home and at school. The only thing different in Gentoo (that I can think of) is the kernel. In 7.3, I was using 2.4.18 and now in Gentoo I am using 2.4.19.

What the heck is going on???????

pjp · Administrator Joined: 16 Apr 2002 Posts: 20067

In case you don't have it installed yet:

mglauche · Posted: Thu Oct 17, 2002 5:54 pm Post subject:

@kanuslupus: what ? no tcpdump installed ? how can you live without it ?

BackSeat · Posted: Thu Oct 17, 2002 7:23 pm Post subject:

What is the output of 'ifconfig'?

BS

pjp · Administrator Joined: 16 Apr 2002 Posts: 20067

adastra · Tux's lil' helper Joined: 16 Oct 2002 Posts: 106

I have installed tcpdump but really don't know what I am looking at or what I am looking for.

I run it on my laptop and I get some messages about ARP "who-has" and then some hostname (not the hostname of the computer I am trying to connect to or the hostname of my Gentoo box). But I also get these messages on a successful ping to a known host (say yahoo.com). I can't decipher it. Running tcpdump on the Debian-SF box I am trying to get to doesn't really help because there are so many packets hitting that thing I can't see which are mine.

I am certain that this has something to do with my Gentoo not being able to decipher the replies that are coming back from the Debian-SF box (but then that wouldn't explain why I can't connect to it with a web browser, would it?). I'm lost on this one. If I can't get it working I will have to re-image back to Redhat but I really don't want to do that but I really need access to this box!!

adastra · Tux's lil' helper Joined: 16 Oct 2002 Posts: 106

Oh my god, I am the biggest idiot in the entire f*ing world. Sorry to cuss and waste all of your precious time like this. You guys have been amazing by the way and I must say that this is by far the coolest, most helpful community in the Linux world. Madd props to you all.

I had the incorrect IP address specified in my /etc/hosts file. Nuff said. You guys have a nice life, I'm going to go kill myself now

Later.