[OT] PPPoA->PPPoE gateway

[Tim Watts]

It's OT but there are a lot of computing dudes here, including me, but I know bugger all about the inner workings of DSL...

Anyway, is it likley that a typical ADSL router can be made to act like a Vigor 100/120 PPPoA->PPPoE gateway?

I have 2 ADSL routers: Solwise SAR715 and Zyxel P-660HW-T1.

A Vigor 120

as a PPPoA to PPPoE converter, effectively funnelling the PPP session on to another device, which is what I want.

In this case the other device will be an OpenWRT box.

Why? Well, I'd like to handle the PPP endpoint myself to terminate both IPv4 and IPv6 natively.

I've been through every option I can find on both ADSL routers, including the promising looking "PPPoE passthrough" on the Zyxel, but no option combination actually presents any PPPoE packets at the NICs.

I just wanted to do a sanity check before I go any buy a Vigor, or a DSL model that can handle OpenWRT...

Cheers

Tim

[Andy Burns]

I too use openWRT, but have never got round to trying PPPoE to the ADSL device (of which I have a wide selection Cisco, Zyxel, 2wire, BThomehub2, Westell, Siemens/Efficient) several of them have bridge modes that look promising ...

I think the Vigor 120 is a true ADSL->ethernet modem, and was considering one myself at one point, One disaantage I think is that once connected you can't get S/N, atten, BER type stats from the modem.

Do report progress ;-)

[Gordon Henderson]

Some can, and some use a sort of half-baked approach. The trick, AIUI is to work out which end is doing the PPP session - ie. username/password in the modem/router device or in your own separate router...

Did you wait to see, or did you poke some PPP packets towards it? You need to do the latter as the "network" is simply sitting there waiting for you to connect to it...

The Vigor 120 is fine, but the MTU is limited to 1492, then you might need to drop it further to get IPv6 through it. I'm using 1486 on my Ethernet interface that faces my V120.

However, it's what I use in my home/office to a Linux router (Entanet ISP, native IPv6). Make sure you get the latest firmware on it as earlier ones wouldn't pass IPv6.. And also setup a dummy interface on the Ethernet port pointing to it as it will initialise itself as 192.168.1.1 and offer DHCP (which you can turn off), but being able to access it out of band is handy to check for the line stats, etc.

The Billion 7800 can be reflashed with IPv6 capable software if you want native IPv6, but might not be as flexable as OpenWRT, etc.

Gordon

[Tim Watts]

Hi Gordon,

I'm clear on that - I want to handle the PPP senssion (passwords etc) at the linux end.

Yep - I had a PPPoE client running. It was sending packets, but none coming back (tcpdump).

Ok - that is interesting.

Thanks :)

Tim

[John Rumm]

You can - but you need to cheat!

Rather than connecting the WAN port of your router directly to the ethernet interface of the modem, do it via your LAN switch after configuring its management interface to be on the same subnet (but unique IP) as the rest of the LAN. You can then see the management interface of the modem from the LAN in the normal way. (the PPPoE frames will also be visible on the LAN, but most modern switches will restrict those to the relevant network ports).

[John Rumm]

From memory, the 715 did not have the ability to export a PPPoE interface. I don't know the Zyxel well enough to comment.

Alas most of the routers that support PPPoE will only do so from the router onwards - i.e. they can connect when configured with all the settings themselves, but can't just act like a true PPPoE modem and allow an external client to furnish the PPPoE termination.

Indeed.

[Tim Watts]

Thanks John - I'll go and buy a Vigor before they go out of fashion :)

Tim

[Gordon Henderson]

If connecting to a Linux based router, you simply configure an alias on the network port - so the main port is up, but unconfigured and an alias has (e.g.) 192.168.1.2 - the V120 itself is 192.168.1.1 by default.

So:

$ ifconfig eth0 eth0 Link encap:Ethernet HWaddr 00:06:4f:66:ad:fe ..etc. (no IP configuration)

$ ifconfig eth0:1 eth0:1 Link encap:Ethernet HWaddr 00:06:4f:66:ad:fe inet addr:192.168.1.2 Bcast:192.168.1.255 Mask:255.255.255.0 etc.

then with some clever routing you can get to http://192.168.1.1/ login (user admin, no password) and view the status page.. e.g.:

can also set syslogging up on it to log SNR changes, etc.

(And don't tell anyone, but you can even use them as cheap routers too - they actually have all the routing code built into them, but default to bridge mode - basically a highly cut-down Draytek 2820 ...)

Gordon

[John Rumm]

I changed my 120 to have its management interface on .1.2, and left the main 2820 on .1.1. then connected the 120 to one of the four internal LAN ports on the 2820, and another looped back to its WAN2 port. A third then connects to my main gigabit switch.

It all used to work well, but these days I get odd intermittent losses of routing to WAN2, that are fixed by rebooting the 2820. At first I thought it was an ISP or ADSL problem, but it does not seem to be.

The size of the firmware image would suggest its more than just a modem! ;-)

[Tim Watts]

Vigor 120 arroived this morning. Tested it against my linux laptop with PPPoE and all works beautifully - IPv4 and IPv6 native up and tested.

Disturbing how dark the IPv6 internet is (I disabled IPv4 for fun)...

As to the question of getting to the Vigor's management interface, others had solutions, but essentially it is only a case of giving it a local IPv4 subnet (eg 10.0.250.1/24 as I did) between it and the router and adding a static route if necessary so the other local PCs can get to it.

One word of warning- if attempting to flash it (I always attempt a flash of new equipment to highlight problems before I go live):

draytek.co.uk appear to only have the V1 firmware up on the site and then you spend hours being confused as to why it will not flash, or you partially succeed but the webserver falls off (broken filesystem) leaving you with telnet, ftp and tftp.

After discovering ftp.draytek.com via the Australian draytek site (which is less crap than the UK one), I discovered the correct firmware:

ftp://ftp.draytek.com/Vigor120%20V2/Firmware/V3.2.6/AnnexA/Vigor120_V2_v3.2.6_AnnexA_332201.zip

(we always have 332201 series in UK, Annex A (or otherwise is written on the router's label).

Bit of TFTP later and it lives again...

But the telnet interface is useful for getting stats (time for an "expect" script)...

Tim

[Gordon Henderson]

Hm. that's newer than what I flashed mine with last - 3.2.4.4 - wonder if it's any different...

I scrape them out of syslog into MRTG

Syslog lines look like:

Jun 3 12:13:37 adslmodem.drogon.net Vigor: ADSL_Status:[Mode=G.DMT States=SHOWTIME UpSpeed=832000 DownSpeed=8128000 SNR=14 Atten=25 ]

scraper:

#!/bin/sh

fgrep "Vigor: ADSL_Status" /var/log/messages | \ tail -1 | \ awk '{printf "%s %s\n", $10, $11}' | \ sed -e 's/=/ /g' | \ awk '{printf "%s\n%s\n---\nSNR and Loop in dB\n", $2, $4}'

Mrtg graph:

(snapshot)

Gordon

[Tim Watts]

Hey thanks for that - syslog sounds a minimally painful way to go...

Cheers

Tim

[The Nomad]

OK, I know I (sort of) understand _what_ you have done, but I can't figure out _how_ you did it ...

Any chance of a how-to or step-by-step guide or url?

My set up is a Vigor 120 -> Monowall (on a PC Engines ALIX) -> gigabit switch.

Thanks & regards

Nick

[John Rumm]

Not sure if that is doable when the 120 is connected indirectly to the lan via the WAN2 port of a Vigor 2820 dual wan router....?

[Tim Watts]

Sure - I'll have it on my blog once I have configured the OpenWRT box.

[Tim Watts]

Can't you have routing (with static rules if necessary) bewteen the WAN ports on a 2820?

I don't know - but all the routing modems I've had before have allowed arbitrary routing rules to be added...

[The Nomad]

Not sure I know where your blog is but no doubt you'll let us know in due time.

N

[Tim Watts]

I've managed to get the web page from the other side of my linux router.

Bit obscure...

telnet into the 120 and do:

ip route add 0.0.0.0 0.0.0.0 10.0.250.1 lan

(Replace the IP above to suit local conditions, the 10.0.250.1 refers to the interface on the linux router that's connected to the 120. Obviously, we assume the router knows what it's doing - but as it's your router, that should be a given :)

Strangely, it does not seem possible to set routing in the web interface!

The hard part is to get it to save that to the boot config:

sys commit

but sometimes, you seem to have to do the whole thing a couple of times before it sticks.

This guide is *very* useful:

[John Rumm]

OK, might have a play with that...[1] I had been experimenting with the static route capability in the 2820s web interface, rather than attempting to do anything on the 120s.

[1] Although without routing to the 120 one can't telnet either! Having said that, this is a slightly academic exercise, since I am not short of lan ports, and so using a pair to loop the 120s connection through the LAN is not great loss.

The 2820 has nice static route section where you can specify a destination IP and netmask, and a gateway IP as well as select which network interface to use (from a choice of LAN, WAN1, or WAN2). But alas it does not seem to achieve anything...

Drop me an email...

[Tim Watts]

It's OK John, thanks - I found the definitve on ftp.draytek.com :)