quick pppoa howto. get the ip and bypass the router nat

hi all,
i have an Adsl internet connection with the tiscali
provider
and i just solved my problem of getting the IP address on my
openbsd machine.
i wish to share my experience here, feel free to correct my
english :P

tiscali's adsl support only pppoa protocol (rfc 2364) and
this is a problem
if you want to connect with pppoe with a modem/router with
ethernet port
and you don't want to be natted behind the router.
i tried the so called "Bridge Mode Only" without
success while i
succesfully used
it on another adsl line with pppoe protocol configured by
the ISP.
The trick come out with the last router's firmware update.
The new firmware let
me flag an "Half Bridge" mode.
I own a Linksys am200 (annex A) router, you should check if
your model support
half bridge if you want to try this configuration.
Once in Half Bridge the router connect with pppoa to the ISP
router,
log on with pap/chap
and give you the public IP with dbcp protocol, after this it
start to
work as half bridge:
copy the IP packets from the ethernet to the pppoa channel
and vice versa.

to configure the openbsd box is very simple,
just put in /etc/hostname.nfe0 (change with your lan card
name):
dhcp up
!route add -host 213.205.24.16 -interface -link nfe0 -expire
1
!route add default 213.205.24.16

change 213.205.24.16 with the gateway's IP of your ISP
(i check this on the router's web administration page, it
never change for me),
also change "nfe0" with your lan card.
you can try without the 2 "route add"  command if
it works, i had to use them
because the gateway is on a different subnet of my public IP
and the dhclient
command doesn't configure it automatically (anyone know
another
solution to this?).

regards
Luigi

Hi,
i wish to share a simple patch to bypass the problem showed
in my previous mail.
the patch fix 2 problems:
1- with the original "/sbin/dhclient-script"  you
don't get the
default gateway if it is
on a different subnet then your IP.

2- when you put down the interface with "ifconfig rl0
down" and then you
rerun "dhclient rl0" , you don't get the IP
configured and with a
little of debug i
found the the dhclient-script execute:
ifconfig rl0 inet 84.223.120.116 netmask 255.255.255.255
broadcast
84.223.120.116
ifconfig: SIOCAIFADDR: File exists

the problem is that you have a route that conflict with the
command:
84.223.120.116/32  link#3             UC          0        0
     -   rl0

the route is added the first time and didn't get deleted on
a FAIL event
(the env is not set by dhclient, i don't know why).
the second time you run "dhclient rl0" the old_IP
and the new_IP is
the same and so
the  delete_old_routes is not executed.
i corrected the problem commenting out the line:
route add $new_ip_address 127.0.0.1 >/dev/null
2>&1

since when you normally configure a static IP address you
don't
configure such route
(please if you know a reason to leave this route let me
know).

here the patch to /sbin/dhclient-script:

# diff -u /sbin/dhclient-script  dhclient-script.patched
--- /sbin/dhclient-script       Sun Mar 11 02:39:21 2007
+++ dhclient-script.patched     Mon May 28 22:48:25 2007
 -37,7
+37,7 
                $medium

        # XXX Original TIMEOUT code did not do this unless
$new_routers was set?
-       route add $new_ip_address 127.0.0.1 >/dev/null
2>&1
+       #route add $new_ip_address 127.0.0.1 >/dev/null
2>&1
 }

 delete_old_alias() {
 -76,6
+76,9 
        for router in $new_routers; do
                if [ "$new_ip_address" =
"$router" ]; then
                        route add default -iface $router
>/dev/null 2>&1
+               elif [ "$new_subnet_mask" =
"255.255.255.255" ]; then
+                       route add -host $router -interface
-link
$interface -expire 1 >> /tmp/dhcp.log
+                       route add default $router >>
/tmp/dhcp.log
                else
                        route add default $router
>/dev/null 2>&1
                fi

EOF


regards
Luigi


On 5/22/07, Luigi Tarenga <luigi.tarengagmail.com> wrote:
> hi all,
> i have an Adsl internet connection with the tiscali
provider
> and i just solved my problem of getting the IP address
on my openbsd machine.
> i wish to share my experience here, feel free to
correct my english :P
[...snip...]
> you can try without the 2 "route add" 
command if it works, i had to use them
> because the gateway is on a different subnet of my
public IP and the dhclient
> command doesn't configure it automatically (anyone know
another
> solution to this?).