APLawrence.com -  Resources for Unix and Linux Systems, Bloggers and the self-employed

ping and telnet dhcp network routing

© December 2004 (various authors)

What is this stuff?

If this isn't exactly what you wanted, please try our Search (there's a LOT of techy and non-techy stuff here about Linux, Unix, Mac OS X and just computers in general!):

From: Tony Lawrence <tony@aplawrence.com>
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 and, 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 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: 

Got something to add? Send me email.

(OLDER)    <- More Stuff -> (NEWER)    (NEWEST)   

Printer Friendly Version

-> ping and telnet dhcp network routing ––>Re: SCO and ping/telnet

Inexpensive and informative Apple related e-books:

Take Control of Automating Your Mac

Take Control of iCloud, Fifth Edition

iOS 8: A Take Control Crash Course

Are Your Bits Flipped?

Take Control of Pages

Printer Friendly Version

Have you tried Searching this site?

This is a Unix/Linux resource website. It contains technical articles about Unix, Linux and general computing related subjects, opinion, news, help files, how-to's, tutorials and more.

Contact us

Printer Friendly Version

Anyone who slaps a 'this page is best viewed with Browser X' label on a Web page appears to be yearning for the bad old days, before the Web, when you had very little chance of reading a document written on another computer, another word processor, or another network. (Tim Berners-Lee)

Linux posts

Troubleshooting posts

This post tagged:




Unix/Linux Consultants

Skills Tests

Unix/Linux Book Reviews

My Unix/Linux Troubleshooting Book

This site runs on Linode