Re: [Linux-ATM-General] About a bridged modem/router, and RFC 1483

[Zoran S. <zor...@dk...>]

Just got to my @ back. :(

Llu=EDs Batlle wrote:

>Hi :)
>Thanks!
>
>I understand about bridging. I tried some ARP pings (arp requests)
>having the modem in "Bridge" mode. I tried for all the hosts in
>MY_PUBLIC_IP/24. So, about 255 hosts I tried. And I got no single
>answer to my ARP requests.
>I should receive answers, isn't it?
> =20
>
Yes. There are various reasons why it did not work. One
possible is that you should reconfigure your IP subnets.

You have between LAN-Firewall one IP subnet /24.
The second one between Firewall and the modem.
The third one from the modem to ISP/net.

If you configured Modem to be in Bridged mode, the modem's IP
interfaces should be removed, and ports put in promiscuos mode:

IPsubnet1\24=3D>[Modem doing NAT]<=3DIPsubnet2\24 both IP addresses shoul=
d be removed,
and all the modem ports should be put to the bridge, and to the promiscou=
s mode.


(LAN)-------[Linux Firewall doing NAT]----[Modem doing NAT]-----(ISP, Int=
ernet)


>For not flooding the ADSL bridge, I connected my computer and the
>bridge through a single ethernet crossed cable. So only my arp
>requests appeared there. And specting with "tcpdump" the ethernet
>where the modem (Bridge), using promiscous mode, there was no packet.
>Well, only my ARP requests.
> =20
>
Maybe you did not finished configuring your bridge. I do not know
which bridge software your modem is using, check out brctl software,
Linux based, and commands. If it is Linux based, it ALSO should have
flag ip_forward set in Linux kernel (check out /proc/sys/net/ipv4,
file name ip_forward). Please, note that I'm typing this off the top of
my head!

My script for configuring brctl looks like (just example):

## -p 0 - routed, -p 1 bridged funcionalities
br2684ctl -b -c 0 -p 1 -a 0.0.40
##-------------------------------------------------------------
## Both interfaces: eth0, nas0 are gonna be part of the bridge
##-------------------------------------------------------------
ifconfig nas0 promisc up
ifconfig eth0 promisc up
ifconfig nas0 # display on screen
ifconfig eth0 # display on screen
## Create Bridge
brctl addbr bridge0
## Spanning Tree Protocol disabled!
brctl stp bridge0 off
brctl addif bridge0 eth0
brctl addif bridge0 nas0
ifconfig bridge0 up
brctl show

>Ah, my Linux firewall is between my LAN and the modem.
>(LAN)-------[Linux Firewall doing NAT]----[Modem doing NAT]-----(ISP, In=
ternet)
> =20
>
At the end, you should have just two IP subnets, your internal between
LAN and Linux Firewall, and public between Linux Firewall and ISP, where
yout Firewall is performing NAT. Modem is in bridged mode, so NO IP
interfaces there, only bridge correctly configured (as I tried to describ=
e
above).

Hope this helps.

Best Regards,
Zoran