Re: [LARTC] Multi-Link Machine

["Martin A. Brown" <mabrown-lartc@securepipe.com>]

Brad,

 : G'day, I had a quick search through the archives to try and find an
 : answer but I have come up with a blank, so I'm hoping I can get a
 : little help here.

Probably a difficulty of terminology, rather than a difficulty with
finding questions and answers on the multi-link router.....

 : I have a linux machine with 2.4.19 on it, and 2 Internet links.

Right.  /me too!  :)

This is a NATting multi-link router.....(which is also not uncommon).

 : eth0 is Telstra Bigpond Cable (Semi static ip, its dhcp assigned), which I
 : want to route certain ips ranges over this link. 144.135.23.0/24 for eg.

Right....so: "ip route add 144.135.23.0/24 via $TELSTRA_ROUTER".  You
appear to have that down:

 : [1] route add -net ip.add.re.ss netmask 255.255.255.255 gw <gw ip of eth0>
 :
 : I can get this to sort of work, but traceroute'ing to anything I set
 : static routes [1] with, doesn't work because I assume that it trys to come
 : back via the default route. Is that right?

Eh?  What do you mean?  The routing table on your linux router has nothing
to do with the upstream routers.  Your linux box should NAT to an IP in
the network range of the interface from which you wish to send the packet.
(Clunky sentence, I know...)

Example, since the IP on eth0 is dynamic:

  iptables -t POSTROUTING -d 144.135.23.0/24 -o eth0 -j MASQUERADE

The packet will leave with the source address currently on eth0.  So, if
you are tracerouting to any IP in 144.135.23.0/24, you should see packets
on eth0 (transmitted with increasing TTLs) from this source address.  Try
it for yourself, and examine the packets with tcpdump:

  tcpdump -nn -i eth0 udp

 : eth2 is an adsl connection with a static ip which I want to be the default
 : route for any traffic left over.

Yup.  There's no traffic left over after a default route!

 : Also I need to break the adsl connection into 2 parts, its a 512kbit link,
 : so I would like to take 384kbit and 128kbit of the link, and assign
 : 128kbit to 192.168.0.192/27 which would be done on eth1, but I don't want
 : to limit traffic coming from eth0. (eth0 is 9mbit, so its a bit of a waste
 : to shape it down to 128kbit now isnt it :)

I presume you mean you want to split the available bandwidth.  This is
traffic control, and you can accomplish this with tc.  Read

  http://lartc.org/howto/  # -- linux advanced routing and traffic control
  http://docum.org/        # -- Stef Coene's thorough site

You might benefit most by starting with this:

  http://docum.org/stef.coene/qos/docs/BB/BB.html

And....

  A router can only shape what it sends.

Remember the above always.

 : Is any of this possible or am I just dreaming?

Dreaming indeed.  Dream your way right on over into traffic control and
policy routing with linux.  It's a dream to work with linux.

-Martin

-- 
Martin A. Brown --- SecurePipe, Inc. --- mabrown@securepipe.com

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