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Routing multiple IP addresses to Dialup user

Q010797 asked
Medium Priority
Last Modified: 2010-03-18
Hey all..

I want to route a number of IP addresses via one of my dialup modems.  Is there a text file I can look at to explain how to do this?  am I best doing this in linux or on my ascend P50 router?
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Best way is setting up a radius deamon on your linux machine, and use your ascend router. Radius can do authetication and tell your router what IP number to use.


Radius will route multiple IPs via a dialup will it?  But users dial into the linux box via analogue dialins.  They don't actually dial into the router.  Can I use the router itself to setup a new route for IP's to a dialup?  Or is there something I can setup in linux to do this without the router?

Is this a dedicated dialup? ie. do they get the same ip everytime?


yes.. yes they do..
This user that wants multiple ips on a dialup... are they going to have all the ips configed on one server machine, or several different machines? If all the IP addresses are going to be configured to one machine, it should be very easy. Otherwise you will probably need to subnetwork a bit, unless you could somehow make it bridge instead of route.

I don't think an Ascend Pipeline 50 talks RADIUS, does it?
If it doesn't, create an entry in the pipeline that routes the IP adresses to the user.
Make sure that it's a subnet, and not some separate IP adresses.


yea they want it over a number of PC's . . can you explain the advantages / disadvantages from bridging the IP's instead of routing.. I would rather route them from what I've been told.

If I use the Pipeline 50 to route the IP's... I need to do it in the format aaa.bbb.ccc.ddd/xx

how do I work out the value of the xx for the ip's I want to route?

To do it in Linux, just use:

route add a.b.c.d pppx

Where a.b.c.d is the IP address and pppx is the interface they are attached to.  You may have to do a grep to find out which ppp interface they are attached to if you have multiple ppp interfaces.

Couple things to consider.  

1) If routing multiple single IP's, you'll need to make sure that the customers end is setup to not route them back over the dialup.

2) Might be wise to route a subnet over to them, like a 240 or something.   In which case you'd use something like this:

route add -net a.b.c.d netmask pppx

Remember that the net is not the IP address in this case, rather the subnet address, so in the case of 1.2.3.*, it might be something like network subnet mask

Hope that helps.


yea it does.. just need a little more detail...  can you explain what routing over to them would give them?  which IP's ?  what would I route to give them more or less IP's?  and how do I know if they are routing the IP's back over the dialup ?

A 240 subnet gives two blocks of 64 IP addresses, you'd keep one and route the other to the customer.  To subnet into more than 2 segments, you could use a subnet of 248 for example.

For information about how to subnet check out the RFC 950 at:

Also there is some documentation at:

You can also search the web for "subnet calculator" for tools to help aid in calculating the network/subnet.  

One word of caution, is that you should read up a bit on subnetting first otherwise you may end up segmenting out currently assigned addresses.

If subnetting confuses you and you just need to send a few IP's over, it would be much easier to just do:

route add a.b.c.1 pppx
route add a.b.c.2 pppx
route add a.b.c.3 pppx


is it possible to route them to an IP address instead of an interface?  I have no way of running a script when the user logs in or out.  But their IP is always the same.
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yea that sounds like a winner :)
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