[ale] Problem with PPP over null modem

[Lex Spoon]

> I'm having trouble getting a ppp perfectly configured over a direct
> serial connection.
> Here's my present configuration:
> 
> null-modem
>  papa-bear   <== ethernet ==> mama-bear <---- ppp ----> baby-bear
>  (171.16.1.2 eth)                     (171.16.1.1
> eth)                    (171.16.10.197 ppp)
>                                                (171.16.10.196 ppp)
> 
[pppd works, but papa doesn't see baby]

First, have you read the Linux Network Administrator's Guide?  It's
very nice; it's where I learned pretty much everything I know about
networking in Unixish environments.  A cool thing about Linux is
that you can do about any low-level thing you want, once you've
figured out just what you want to do.


Anyway, it sounds like you just need to set up some routing.  In
particular, papa-bear must be told somehow that baby-bear exists and
can be reached via mama-bear.

If there's just one papa-bear, you can probably get by with running
this on papa-bear:

    route add baby-bear  gw  mama-bear



If there are a lot of papa-bears (such as an Internet full of them),
and you can't add route entries on all of them, here are some ideas
to try.

One possibility is to set up mascarading on mama-bear, and have
mama-bear mascarade baby-bear as herself.  This means you probably
can't run any servers on baby-bear, but it will let you creak along
with www, ftp, and even mail.  Maybe this is good enough for your
interests.  The inaccessibility of any servers on baby-bear might even
be construed as a security measure.


Another interesting possibility would be to give baby-bear a number
used on the ethernet segment (such as 171.16.1.3), and tell mama-bear
to advertise for baby-bear on the ethernet (since baby-bear can't
touch the ethernet itself).  On mama-bear you'd have to do something
like:

    arp -s baby-bear [mama-bear's ethernet address]

mama-bear's ethernet address can be found by running ifconfig on
mama-bear.


Finally, you could install a routing package like gated, which is
designed to deal automatically with complex, changing networks.  I
hear it takes a lot of memory though, and that it is overkill if you
just have a relatively simple network.



hope this helps,

lex