Modem with full-bridge / half-bridge

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art3011

39 posts

Geek

#45128 30-Oct-2009 17:10

I recently decided to get a Linksys WRT54GL router as I've mentioned here http://www.geekzone.co.nz/forums.asp?forumid=66&topicid=44731 . Now it is time to look for a modem. What I wanted to do is to have the modem connect to ISP only, then in half-bridge or full-bridge mode, let the router do NAT, DHCP, port forwarding, Qos, etc. I will be flashing the router with Tomato (or maybe dd-wrt). I would like:

1. A good modem that reliably stays connected to ISP all the time.
2. If connection to ISP disconnects, it must be able to reconnect automatically.
3. If item 2 happens, the router must be able to renew the WAN IP on its own.

I have not done this before, but I have a fair idea on how to configure it. I wanted your opinion on which modem to get.

I am leaning towards getting a Draytek modem because it has PPPoE to PPPoA bridging (or pass through). I understand this is a full-bridge and it is a better implementation than PPPoA half-bridge. I also get the impression that Drayteks are very good modems. If you have a Draytek modem, please let me know your opinion on this modem and your experience with PPPoE to PPPoA bridging.

Getting a Linksys AM300 may be another choice based on discussions here in the forum. With the latest firmware, I understand PPOA half-bridge works reliably.

Please help me choose a modem.

BTW, I'm still on ADSL1 (and not ADSL2), but I don't think that matters.

TIA ... Art

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8219 posts

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#268698 30-Oct-2009 22:33

Draytek's are great but they are expensive $125+ for something that is just doing the adsl connection then passing on to the router, seems a waste to me but if you want the full pppoa to pppoe bridge it's the way to go.

TP Link TD 8840 is a good cheap option ~$70, it's basically the same reliable broadcom chipset as the DSE XH9949 and the Dynalink RTA1320 but it's not as ugly as the DSE and doesn't have the overheating problems the Dynalink has a reputation for.

I would probably give the AM300 a miss as it uses a Texas Instruments chipset, I've heard there have been some problems with compatibilities between TI chipsets and new DSLAMS in some exchanges and cabinets, a problem where the sync speed it limited to 7Mbit max no matter what.

I'm actually using the AM300 at home at the moment but our area hasn't been cabinet'd and we only sync at 4-5Mbit anyway. Half bridge works fine but I used to get a slightly a higher sync speed with a Dynalink RTA1320 before it crapped out.

coffeebaron

6231 posts

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#268798 31-Oct-2009 14:42

Yes, go the Draytek Vigor 120. It will do as you need & works very well. I install quite a few Draytek's, and wouldn't use anything else myself.
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dharmatraveller

25 posts

Geek

#268840 31-Oct-2009 17:37

There is Draytek 120 on Trademe at the moment. Should be a cheaper option.

chriswiggins

413 posts

Ultimate Geek

#268848 31-Oct-2009 18:18

I still use my ol D-link DSL-502T Gen II in half bridge mode. Cheap on trademe and does the trick just fine!

Ragnor

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#269977 4-Nov-2009 12:21

dharmatraveller: There is Draytek 120 on Trademe at the moment. Should be a cheaper option.

The reserve was $10 which is about 1/10th the retail price of a new one but it ended up going for about half price ~$60... seems like quite a few people were interested and someone saved $40-60.

Not me unfortunately.

cr250bromo

222 posts

Master Geek

#270007 4-Nov-2009 14:09

I use a Draytek Vigor2700 on one of my Cisco routers that doesn't have a DSL2+ interface.

Works well and IMHO better than half-bridge. Since the Cisco (or whatever router you use) initiates the ppp connection when using a Draytek in pppoe to pppoa mode, it actually knows when it's got and lost ppp. Useful if you have more than one connection and want to initiate a failover when you've lost ppp (or take some other action).

Using half-bridge, the only way you can tell is when your public IP changes to 192.168.x.x and most devices aren't going to realise this means the WAN connection is down. Depending on the DHCP lease time it could also be a few minutes before the address changes too.

Only small drawback is losing 8 bytes off the MTU, but as long as you configure for that it's no problem.

A+++ to the draytek, would buy again :)

Ragnor

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#270078 4-Nov-2009 16:37

Quite right wouldn't use half bridge for a business connection.

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dharmatraveller

25 posts

Geek

#270209 5-Nov-2009 08:45

I have a Draytek modem for sale on trademe at the moment.

art3011

39 posts

Geek

#270231 5-Nov-2009 09:36

Thank you for all your comments. I ordered a Draytek Vigor 120 a couple of days ago. It now comes with a 9V 1A power adapter and in combination with patching the latest firmware should fix problems with some ADSL2+ DSLAMS (according to snappernet.co.nz).

I'm testing it with the Linksys WRT54GL with the stock firmware. So far so good. After I'm satisfied with my testing, I'll patch the Linksys with Tomato firmware.

Again thanks for your advice.

Ragnor

8219 posts

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#270263 5-Nov-2009 10:32

portunus:

Only small drawback is losing 8 bytes off the MTU, but as long as you configure for that it's no problem.

This is a good point about remembering to change the MTU for pppoe to 1492 (instead of 1500 for pppoa).

However I remember reading something about 1454 being optimal so it breaks down to 30 ATM frames once the various headers are added?

cr250bromo

222 posts

Master Geek

#270286 5-Nov-2009 11:26

mtu is set to 1492 but tcp mss (maximum segment size) gets set to 1452 - mtu minus 40. mtu discovery doesn't always work especially when people block all icmp traffic under the misguided belief it makes them more secure.

the tcp mss doesn't require working icmp but still allows the maximum packet size to be communicated. I suspect this is not an issue with udp given most udp packets are quite small.

sultanoswing

814 posts

Ultimate Geek

#276012 25-Nov-2009 01:15

I just got a Vigor 100 from Trademe (pretty similar to a 120, apparently).

It works only when it's directly connected via its LAN port to my PC and using Windows XP's 'create new connection' which creates a miniPPPoE connection. Accordingly, I'm happy it syncs, works and downloads and is able to successfully passthrough PPPoA>PPPoE.

However, connecting the modem to the 'Internet' port on my WRT54GS running Tomato 1.25 doesn't work. Setting the PPPoE connection in the Tomato web interface and entering my ISP details SHOULD work, but doesn't, with "Connecting...." only, but it never manages to actually connect through the modem.

Lynksys is at 192.168.1.1, subnet 255.255.255.0.
I've tried various IP combinations for the Vigor - same subnet range, different subnet ranges etc. etc. but no luck.

Am I missing something, or do I need to try a vigor 120 to enjoy the same success as you guys??

dharmatraveller

25 posts

Geek

#276079 25-Nov-2009 09:37

That 120 is all you need(smile) Take the Draytek IP back to 192.168.2.x Configure your Tomato to PPPoE connection type and you will be in business providing all the wires are in the right place.

dharmatraveller

25 posts

Geek

#276105 25-Nov-2009 10:34

Sorry typo " That 100 is all you need"" its a tad early for me.

sultanoswing

814 posts

Ultimate Geek

#276292 25-Nov-2009 20:16

dharmatraveller: That 120 is all you need(smile) Take the Draytek IP back to 192.168.2.x Configure your Tomato to PPPoE connection type and you will be in business providing all the wires are in the right place.

Nope still no dice. Frustrating. This better not be a rare hardware problem with my WRT54GS's internet port.

To confirm the settings to use:

On the Draytek 100:
PPPoE / PPPoA Client - enabled
VPI 0
VCI 100
Encapsulation: VC Mux
Modulation: Multimode
PPPoE Passthrough Wired LAN: Checked
? use the default MAC, or set another?
IP Address: 192.168.2.9
Subnet Mask 255.255.255.0 (does it need a different subnet from the router / LAN, which is 255.255.255.0?)
Should I enable the dreytek's DHCP Server? If so, what IP ranges?

On the WRT54GS:
PPPoE Connection enabled with username & password entered as per ISP: xxxxx@adsl.xnet.co.nz
LAN enabled with DHCP 192.168.1.x, subnet mask 255.255.255.0

Anything I'm missing? I'm about to try a different LAN cable in desperation. Oh, and I'm assuming the draytek plugs into the 'Internet' socket of the WRT54GS!

Firmware is Tomato 1.25. I;ve also tried DD-WRT and Tomato 1.26 (beta). All are also not working in PPPoE mode. DHCP half-bridge with my trusty Dynalink 1320 does work.

Hmmmm.....

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