Date: Sat, 4 Aug 2001 8:3:57 From: gjukema@jukeware.com To: questions@freebsd.org Subject: Re: unable to ping through WAN Message-ID: <20010804150645.0ABB137B405@hub.freebsd.org>
next in thread | raw e-mail | index | archive | help
>snip< > > > > Sorry, I didn't mean to say "I know" - and all the documentation I found > > regarding the explanation of subnet masks, I couldn't make sense of, so I > > was only guessing that changing the subnet mask would actually make a > > difference in this scenario. I apologize if my question was inappropriate. > > It just seemed strange that you knew that this was not right, but > hadn't changed it. I suppose I could have explained why I didn't change it, but just felt that wasn't part of the actual problem at hand. Long story short: I don't have any access to the machine, and walking people over the phone with a `guess' as to what's wrong is just no fun - been caught there before and my guesses have usually caused me more trouble. > > BTW - changing the subnet mask did work - but I fail to find an explanation > > that actaully makes sense what the subnet mask actually does, and why > > it would make a difference to the outside WAN. Crist, the following explanation that you provide here is excellent, thank-you. With this and Fernando's reply yesturday, it all makes sense to me. > It doesn't make any difference to anyone but the machine that had the > wrong mask. Looks like the actual addresses of some machines got > snipped, but let's say 10.10.20.100 is the machine with the incorrect, > 255.255.0.0, mask, and 10.10.10.50 is the machine on the other side > of the WAN it wants to talk to. So, our machine takes its address and > does a binary-AND with its netmask, > > 10.10.20.100 & 255.255.0.0 = 10.10.0.0 > > So we have our local network number, 10.10.0.0. Now, let's check if > the remote machine is on our network by taking its address and doing > a binary-AND with our netmask, > > 10.10.10.50 & 255.255.0.0 = 10.10.0.0 > > Its network number is 10.10.0.0 is the same. That means it is on the > same network and directly reachable and we don't need to go through > any routers. > > But this is not the case. The netmask is incorrect, but the computer > doesn't know that. > > > Of course, this isn't a > > FreeBSD question any longer, so I'll shut up now and look elsewhere. > > Any basic tutorial on routing should have this kind of stuff. I have a book that *trys* to explain it - but they came no where near what you and Fernando did. Perhaps the author's didn't actually *know* the real workings of subnet masks and networks - or perhaps I was looking in the wrong place. > > Funny, this is my third question I've asked on the FreeBSD questions list > > since 1998 - and again I feel like an ass for doing it. I guess I'm out > > now - hopefully there's more innings left in this game :) > > I guess the answers just look so-o obvious to others some of the > time. It takes conscious effort to keep from cracking wise, but > sometimes it sneaks through. Except RTFM questions, those I feel free > to let loose on. But it's not as bad as the Linux lists. ;) I can relate. Thanks again, Geoff To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20010804150645.0ABB137B405>