Re: [SLUG] Routing across ethernet and ppp?

[DaZZa <dazza@nospam.zip.com.au>]

On Tue, 2 May 2000, Jason Lowe wrote:

> Computer 1:
> * ppp0: 203.x.x.121 (Direct connection to Telstra Big Pond)
> * eth0: 203.x.x.123

This is your first problem.

Without knowing your subnet masking {but assuming a standard class C mask
of 255.255.255.0}, you have a single machine with two IP addresses on the
same subnet but different interfaces. From memory, this will completely
screw routing. The box won't know which interface to throw packets for the
subnet out on.

> Computer 2:
> * eth0: 203.x.x.122
> 
> The problem: How do I setup routing so that computer 2 can be seen on the
> Internet?

You need to change your ppp0 IP address to the elstra assigned 139.x.x.x
address.

So you end up with this.

Computer 1

ppp0	-	139.x.x.x {Telstra link
eth0	-	203.x.x.1 {Your Ip range}

Computer 2

eth-	-	203.x.x.2 {Your IP range}.

> Computer 1 has a direct connection to the Internet and works fine. We are
> running mail, web and squid to give all internal users access to the
> Internet. Computer 2 cannot be seen from the Internet.
>
> * The ppp0 to telstra is 203.x.x.121 our end which is linked to teltra's
> gateway of 139.x.x.x

Who assigned this address for your gateway? And what subnet mask is being
used?

> * I can ping 139.x.x.x from Computer 1
> * I cannot ping 139.x.x.x from Computer 2
> * I have swapped over IP address on Computer 1 (ppp0) to that on Computer 2
> (eth0) and manage to operate the direct connection correctly. This implies
> that routing on Telstra's end to 203.x.x.12x is correct!
> * Computer 2 can ping 203.x.x.121 and 203.x.x.123 on Computer 1 (They're on
> the same network)

As they should - there's no routing involved - just a direct broadcast.
However, with the two network adapters in the one machine on the same
subnet thing, I wouldn't be surprised if this ping traffic was being
directed out to the net as well as on the local subnet - at least as far
as the Telstra link, anyway.

To say more, I'd need to know your entire setup - IP addresses complete,
and subnet masks, dumps from ifconfig and route etc etc.

DaZZa



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