[nzlug] ADSL modem for pppoe bridge

[Nick 'Zaf' Clifford]

Appologies to all if I'm repeating anything already said.

Half Bridging using DHCP is the most common method in NZ for DSL routers.
Be advised that if you import a DSL router from overseas, it may not
have a NZ Telepermit.

As for Linux having issues, yes, the reason is that the router issues a
DHCP lease with a default route outside of the IP/Netmask of the interface.
Eg: DHCP issues IP=202.36.240.10/255.255.255.0 and a Gateway address of
202.36.1.1
Windows happily handles this (as you've noted). Linux's routing tables
don't off the cuff.
The solution is to create a static host route to the gateway, then set
it as the default route.
eg:
route add -host 202.36.1.1 dev eth0
route add default gw 202.36.1.1 dev eth0

I believe a couple of years ago I posted on this, and provided a patch
to "pump" (dhcp client) which did exactly this (there is no harm if the
gateway IS on the same subnet).

This effect by the way, not only affects Linux, but also Cisco routers,
and Packeteers.
Again, the work around (adding a manual host route) works with this
equipment, but the cavet is that if the ISP changes their routers IP
address (which can, and DOES, happen), then your manual routes fail.

As for the whole thing being a kludge, no kidding. As I understand,
pretty much everywhere else in the world, everyone issues at least 2 IP
addresses. One for your DSL router, and one for your PC. We had a team
from the UK over here for a client, and they were stunned how our ADSL
service worked (or rather, didn't).

If someone does find a reputable, current, available in NZ with
Telepermit, in stock (and predicted to be for awhile) router that does a
PPPoE to PPPoA bridge, then I'd be very interested.

Nick


Peter wrote:
> HI again,
>
> Thanks guys.
> - Linksys AM300 (Firmware 1.19.04 )
> - PCI ADSL modem from Traverse in Australia (work under Linux).
> - Thomson Speedtouch (PPTP with pptp-client)
> - 3com Homeconnect (old)
> - Draytek Vigo r110
> Some familar names in their from my google stint. That last one looks
> very promising, and its probably no coincidence that they are used
> mostly in the UK, becasue UK telecom co's favour PPPoA as does
> telecom. 55 pounds. Maybe we could bring in a box lot?
>
> As for "half bridge", with a static ISP WAN address, its probably an
> acceptable solution. But its a cludge if ever there was one. The first
> link below explains how its acheived[1]. Basically the modem runs
> dhcp, issues you with the public WAN address, itself with WAN+1 as
> gateway, messes with the netmask and hopes that your LAN/downstream
> router can cope with it. Throw in 30 second lease renews and you got
> something of miracle if it actually works.
>
> By way of a little praxis, last week i connected a billion 7100s in
> half bridge[2] working off a dynamic WAN IP, to a windows box .
> Windows didnt even blink. Happy as a larry. Ok, then onto Debian Etch
> with updates. Long silence from route trying to figure out the default
> gateway. There are suggested workarounds in [2], and such things no
> doubt being built into recent releases of wireless router firmwares,
> left right and center.
>
> Regards
>
> Peter
>
>
> [1] about "bridge" and "half bridge" in pppoA territory
> http://whirlpool.net.au/forum-replies-archive.cfm/806160.html (martin
> half way down)
> http://phirate.exorsus.net/wiki/doku.php?id=nz_dsl_modem_networking
> http://www.speedtouch.net.nz/forum/topic.asp?TOPIC_ID=1002
> http://forums.whirlpool.net.au/forum-replies-archive.cfm/941840.html
>
> [2] Getting billion 7100 into half bridge (also works on a wide
> varierty of cheap adsl routers because they pretty much all use the
> same chipset)
> a. Quick start | username and password, PPPoA, VCI etc, reboot,
> confirm connects under NAT.
> b. Configuration | Advanced | Misc Configuration | Half bridge
> c. Configuration | Advanced | Misc Configuration | HTTP Server Port | 81
> d. Go back to Configuration | WAN | pvc0 submit| and return the
> encapsualtion to pppoa VC-MUX, Half bridge alters this wrongly to ppoe
> llc
> e. reboot router, f. use dhcp client downstream and there you have it,
> your WAN ip address on your box, check your firewall.
>
> These and many similar modems support "DMZ", but all this does is NAT
> to a static LAN address, sans firewall. Turn off NAT and DMZ doesnt
> work. This might get around some folks "port forwarding"/virtual
> server issues, but youre still stuck with a weak NAT implementation.
>
>
>
>
>
>
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