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Multiple IP's across PPP

bemidji asked
Medium Priority
Last Modified: 2010-03-17
How do I route multiple (16)  IP's over a PPP dial-in.
ip-up ?       If so, what's the script and syntax ?
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Bhidji, be more specific.
1) Route 16 of your friends to the outside world?
2) Or use 16 different IPs on a single dial-up account?

If it's the first one, that's simple.
Basically, your "friends" will have to put your machine as a "defaultroute" in their ppp scripts and you will have to add the route to them when they log in. Now, if you have legal IPs for all your 16 friends, then it's easy. There's not enough space
to answer all of that here, but you could read the NAG and maybe NET-3-HOWTO. But, if you DON'T have legal IPs for your 16 friends then you'll have to use ip-masquerading. IP Masquerade Mini-HOWTO (http://WWW.REDHAT.COM/linux-info/ldp/HOWTO/mini/IP-Masquerade)
will help you a great deal.

If it's the second one, it's tricky; if all of the IPs you're using are from the same subnet, then it's ok, but if they are from different subnets then it's impossible. Because the router
at the other end (your ISPs router) won't let you.

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sorry pele- here's more info.  The ppp dial-in is on a isp ppp server.  The 16 ip's are internic legal and are for use as virtual domains on my www NT IIS server.  Does address your questions?


Still, you're not telling me if the friends are loging on to your
machine, and using your machine as the gateway to the outside
world, or if you want to use all of the 16 IPs for your own machine.
Or is it something completely different, for example, that your 16 friends are actually on the local ethernet you got in your office?? Then that's even easier. Let's assume for a moment that your machine's IP is
Your subnet is, your netmask is, your broadcast is
When you've dialed in (to your ISP), then I suppose everything works for you? Now...well...first tell me if this is the actual situation and I'll answer, if not, then tell me if which one of the first two is it.


OK PELE - as I stated above the 16 ip's are for VIRTUAL DOMAINS on my www server.  Am I mis-stating something here?

My Nt server will Dial In to an ISP (who is using linux slackware ) via a ppp connection.  The ISP has assigned my server 16 ip's.  
THEY DON'T KNOW HOW to route the static ip's to my name server/virtual domains over the ppp connection.
They have asked me to help them out and fix the routing on THEIR linux box. (not my server) They have one Class C.


Oh so there you are.
Ok, ok, don't panic, calm down, everything will be just fine.
First, if your ISP doesn't know the basics of routing - switch ISPs, my friend. But let's leave that for a moment.
Just tell them to use static routes to your machine (that is if you have the money for the dial-up to be up all the time).
If not, then tell them to add more routes through their ppp interface once you've loged on.
Something like:
route add -host virtualIP1 gw isprouter netmask dev ppp0
route add -host virtualIP2 gw isprouter netmask dev ppp0
and so on. (a script does that)

But, why are you using 16 IPs for your virtual domains?
Just tell them to put aliases on their dns. Or if you're doing dns yourself (which would be a bit odd) then you put the aliases.
That way you only have one IP (and pay less to your ISP, if I'm not wrong), and your webserver should easilly handle that. Different pages for different names.

But there's another question. If you've decided to do some virtual hosting, why are you doing it over a dial-up anyway? Think bigger than the miserable 33.6 you're getting. Or is that an ISDN line? If it is, then you do have call-back-demand don't you?



Pele : You mention many good points.  The IIS server with NT will only do virutal domains (virtual hosts in MS words) with a unique ip for each domain.  The dial-up is only for testing for the next month and then the box is going co-host with a different ISP.  Having them manually add the routes each time I log in has it's drawbacks though.  Their configuration assigns a different ppp# to the tty port each time. A different ISP - would be nice.  I'm in northern minnesota.  Not many choices for local dial-up access.  The other isp didn't even know about static ip's.  Maybe I should Move ?
Since I posted this originally, I've added the appropriate case statement (to check for my port), the route add commands and
a proxy arp to the ip-up.  Hopefully this takes care of it.
Thanks Much for your time.


I forgot to mention subneting. Tell them to subnet their C-class, that way they don't even have to worry about your IPs as you will handle them. Just tell them to make up a subnet IP (say if their C-class is then your subnet will be say) and then tell them to re-calculate the netmask and broadcast for both their own and your subnet (every ISP worth it's salt should know how to) and then tell them to route to your subnet.
something like
route add -host netmask calculatednetmask dev ppp?
route add -net gw yourmachine
and that's it really.
Good luck with your virtual hosting...

P.S. move or employ me for fee and fun to handle all your admin stuff...pele@artewisdom.com
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