ping and telnet dhcp network routing
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From: Tony Lawrence <firstname.lastname@example.org> Newsgroups: comp.unix.sco.misc Subject: Re: SCO and ping/telnet Date: Wed, 03 Oct 2001 11:20:21 GMT Bela Lubkin wrote: > > I would look for a problem in reverse DNS lookups. Start by trying the > "-n" flag in your ping attempts. If that fixes it, the problem is that > ping is getting hung up trying to translate the IP addresses of received > replies back into host names. > > If you let the ping run for a long time, DNS will eventually time out > and you'll see one reply. I assume you are otherwise interrupting the > ping attempts. If you look closely, you should also notice that ping > says something about having received 1 reply in its final summary, even > though you never see the reply itself.
I had an interesting one just last night. A guy calls, says he's adding a SCO box to his home network. Two Windows machines that happily talk to each other, but the SCO won't. I went through the obvious stuff first, but it all sounded fine. Correct supplements, right drivers, good card. All machines 192,168.2.x. Sounds fine. I had him ping the SCO from Windows- he said "that's odd- that didn't work before". I then had him ping from SCO- no response. Must be DNS- had him add the Windows ip to /etc/hosts and try again- but it still didn't work. OK, clear out the arp tables and back to the Windows machine to try a telnet. Doesn't work and doesn't show up in arp. Try a ping again- hmm, doesn't work. But it did work a few minutes ago.. but the arp shows the ping got there. So now I asked him to fully describe his setup- hubs, where everything is plugged, how long are the wires, is it all cat 5, 10/100 what make/model nics.
All good model cards, all brand new cat 5 cables, a little 8 port 10/100 hub.. and a router. A router? Yes, a little internet router-thingy, he says. Does that thingy give the Win machines their ip addresses? Yes, indeedy, he said. Ahh. I asked him to remove the router from the hub and temporarily give the Windows machines static ip addresses. OK, mutter, mutter, fumble, fumble, sound of machines rebooting and Bingo- everything works. Next question. What's the DHCP range this router thingy assigns from? Dunno, he says. Set it up a long time ago, don't remember having to tell it anything, don't know how to get to it. OK, plug it back in, but this time lets give the SCO box a number way the heck away from the numbers the Win machines get. The Win boxes were getting 192.168.2.8 and 192.168.2.10, so give the SCO box 110. Son of a gun, it works. So- apparently this internet router thingy didn't like the SCO box trying to use an ip address in its DHCP pool. Makes sense, but: Why were 192.168.2.0 packets going to the router anyway? Should have just gone through the hub and everybody is happy. Unless.. oh, darn I just realized I forgot to check the netmasks! I'll forgive myself because I was working over the phone completely free of charge and really wanted to get back to other things. I bet that's it. I bet the router gave them a mask that put them down in their own little network. That might explain it. Anyway, this stuff can be fun. Especially flying blind on the other end of the telephone :-) -- Tony Lawrence SCO/Linux Support Tips, How-To's, Tests and more:
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