Re: pppd question with Redhat (hopefully simple)

["Andrew F. Seila" <andy ms cba uga edu>]

On Sun, 24 May 1998, Mark Conway Wirt wrote:

> 
> Now that my UDB is up and running (thanks to everyone on the list!), I've
> decided to put it on the net using a PCMCIA modem and pppd -- easier than
> carrying it to the office to plug it into our Ethernet ;-)  I've gotten it
> to work, but only by the following magic:
> 
>    1) Make sure that the Ethernet card is enabled.
>    2) Make the connection.
>    3) Disable the Ethernet card, thus clearing the route cache.
>    4) Add a route the the remote terminal server by hand.
>    5) Add a default gateway pointing to the remote terminal server.
> 
> !
> 
> Whenever the Ethernet card is up, I get "Network Unreachable" messages
> when pppd tries to add the routes.  This is true in all cases: using a
> statically assigned IP address from the same subnet on which the Ethernet
> resides; using a dynamically allocated IP from a different subnet; and
> using terminal servers from different subnets (different dial-in
> locations), including and excluding the subnet of the Ethernet card.
> 
> Anyone seen this behavior, and know a fix?  As I said, it works, but it's
> a bit of a pain...
> 
I had this problem on a Linux/Intel box.  The problem is a routing 
issue.  The networking code in the kernel cannot figure out where to send 
ip packets.  You probably have a subnet setup for your ethernet card, and 
the default route points to a machine on the subnet (or something).  In 
my case, the machine on the other end of the ppp link was on the same 
subnet as the machine on the local end of the ppp link.  The 
solution that worked for me was to setup static routes to each machine on 
the subnet, and a default route to the machine on the other end of the 
ppp link.  Since I have about 6 machines on my local network, this was 
not too hard to do.  If your local net is really big, you will need to 
figure a different solution.  The solution (without IP masquerading) is 
to either setup static routes for machines on the remote end of the ppp 
link or define a different subnet on that end.  

I hope this rambling helps.  It would be helpful to know the details of 
your routing table.

Andy Seila

Andrew F. Seila				e-mail       andy@ms.cba.uga.edu
Terry College of Business		voice campus        706-542-4290
201 Brooks Hall				fax campus          706-542-4295
The University of Georgia
Athens,  GA  30602-6255