question about setting routing

Rob Landley rob at landley.net
Mon Mar 20 17:15:40 UTC 2006


On Monday 20 March 2006 7:20 am, Dariusz Zmokly wrote:
> Hi,
>
> I've just bought Pentagram's Cerberus router. It contains BusyBox
> v0.61 pre (2005-09-23).

A quick google for that brought up a page in polish, but I can't find any 
mention of source code.  (This could just be that I don't know the polish 
phrase for "source code"...)

> It has 4 ethernet ports. To the first port I've plugged network cable
> from my wireless internet modem. So I have three ports left.
>
> When I plug a cable from my computer into second port I can use
> internet. BusyBox acts just as a bridge.

Busybox does not, your hub does that entirely in hardware.

> So I get an IP address via 
> DHCP request from wireless modem.

The dhcp server is probably ours, yes.

> What I'm trying to do is to configure BusyBox as a firewall with NAT.

Technically speaking, you're trying to configure the Linux kernel as a 
firewall with nat.

> However I've problems with it ;) | logged into a BusyBox and issued
> command 'udhcpc' and it worked. BusyBox got an IP address from modem.
> But for some reason it can't ping wireless modem (this modem is
> pingable from my computer when I run 'iptables /renew' on it).

1) Did it actually set up the interface correctly?  Type "ifconfig" and see 
what addresses the various interfaces have, and whether they look right.

2) I have no idea how your firewall rules are set up.

3) For no apparent reason, ping requires root access.  (This is a kernel 
thing, not us.)  Are you running as root when you ping, or did they set the 
suid bit on busybox?

> Obviously DNS resolving doesn't work as well.

So udhcpc claimed to succeed, but you didn't actually get a usable connection.  
Note that udhcpc works with broadcast packets in promiscuous mode, so routing 
simply isn't an issue.

Do you have any previous familiarity with Linux networking?

> So there is some problem 
> with routing but I have no idea where.
>
> Could you give me some suggestions?

http://www.oreilly.com/catalog/linag2/book/index.html

Rob
-- 
Never bet against the cheap plastic solution.



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