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Any one using an ADSL modem in bridged mode?

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Any one using an ADSL modem in bridged mode?

Hi There,

I have a WatchGuard firewall and I want to present it with my external IP address rather than an internal 192.168.x.x, then have the WG act as DHCP server to my LAN side.

I have a Linksys ASDL2MUE modem, and it has an option for bridged mode. But I am quite confused as to how this works. Is it possible for this to work with only one public IP address?

Any help or suggestions greatly appreciated.

Regards

Chris
11 REPLIES
oliverb
Grafter
Posts: 606
Registered: 02-08-2007

Bridged mode

http://www.adslguide.org.uk/hardware/reviews/2005/q4/linksysADSL2.asp

It looks as if bridged mode needs the firewall to be configured for PPPoE. I think this only works if your exchange supports PPPoE, but I could be wrong there. Anyway a number of areas can use PPPoE mode in place of PPPoA now.

Otherwise you need a modem/router that supports ZIPB or a one to one NAT mode I think.
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Any one using an ADSL modem in bridged mode?

I had found the very same web site. I wasn't sure I could chance going to site and finding I can't set it up for PPoA. In fact when I got my welcome message from PN they explicitly say PPoA only - Doh.

So I searched further and ordered a D-Link DSL-300T, there are mixed reviews all over the net with regards to this one some people love it some hate it. I think hate it because people buy it thinking it will be a router and firewall etc, when it is just a modem. Any way I digress. It should arrive today and I will test it out, as they claim it can do what I want with PPoA this may just be 1 - 1 NAT or some sort of bridged modeHuh

Will report back when I have more info.

Chris
oliverb
Grafter
Posts: 606
Registered: 02-08-2007

Any one using an ADSL modem in bridged mode?

It looks right judging by the review. I've done the same trick with an old Solwise SAR110 router when I wanted to play an online game that wasn't NAT-aware. It's a form of bridging but at IP level. The trick is that both the modem and the firewall have the same public IP address so the firewall appears to be connected directly to the ISP even though there's really a router in between.
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Any one using an ADSL modem in bridged mode?

I use a D-Link DSL 300-T in bridge mode with a DGL 4300 router and it works great. The bridge mode allows either the PC or router to handle NAT which usually dedicated modems are poor at doing themselves. The router or PC needs to be set to use PPPoE but this is not a problem as even though plusnet use PPPoA this is only over the telephone cables so the modem converts it into point to point protocol over Ethernet to send it over Ethernet cables to the router. So in short using your modem in the way you describe with your PC should work fine.
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Any one using an ADSL modem in bridged mode?

The D-Link DSL-300T arrived from DSL-Warehouse.co.uk, must say very quick delivery and plenty of communication. Any way, got it out the box set it up and had a poke round the config.

I have to say I was so doubtful I called D-Link and spoke to their technical people who assured me it would be fin in PPoA and even though the DSL-300T is set to give out DHCP addresses on a private LAN.

Whizzed off to site and plumbed it all in connected the D-Link directly to my laptop and bingo got an internal address, set up all the config, rebooted it and then got my PN fixed IP on the laptop. I was so excited I nearly got a round in.

Set up on the WatchGuard went ok, but try as I might I could not browse the net and when I tried to configure it's WAN IP manually it moaned about the 255.255.255.255 net mask, so I set that to DHCP. Still no joy. Phoned WG as I had paid a heft chunk for silver support, and they say it has to be on a different IP address from the modem, so I need more IP addresses or I could use NAT - exactly what I was trying to avoid in the first place.

I have no requested additional IP addresses from PN, does any one know how long they take to set up?

Thanks again guys...
oliverb
Grafter
Posts: 606
Registered: 02-08-2007

Any one using an ADSL modem in bridged mode?

Before you go to the extreme of multiple IP you could try giving the WG a subnet mask of 255.255.255.0, 255.255.255.240 or 255.255.255.252

Some equipment won't tolerate 255.255.255.255 as it defines a subnet of one. The drawback of setting a mask is that there will be a small number of addresses close to yours that will be inaccessable.

255.255.255.252 should be the smallest "legal" subnet.
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Any one using an ADSL modem in bridged mode?

Hi, Thanks for your continued suggestions. I had looked at using a /30 as it does give one usable address. How ever I am not sure if the WG is complaining because it wants an IP address different to the default gateway.

I will test it out.

Thanks

Chris
oliverb
Grafter
Posts: 606
Registered: 02-08-2007

Any one using an ADSL modem in bridged mode?

Regarding the default gateway on the WG, that probably should be the private IP address of the D-Link (192.168.xxx.xxx). You might want to repeat the D-Link to Laptop direct test and note down the values the laptop detects.
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Any one using an ADSL modem in bridged mode?

There is something strange going on!

I raised a ticket and was duly assigned a block of four addresses on my business account. I also made the same request on my personal account so I could test the hardware before going to site again. Unfortunately I had to go to site before I had chance to test on my personal account.

I connected the D-Link to the line and directly to my laptop, it connected up ok and gave me the Router address via DHCP I was expecting, but I was unable to direct any traffic to the Internet.

I checked and rechecked the config, couldn’t find anything wrong at all. I then checked my email (on another connection) and found the block of four had been added to my personal account. So I logged in using that account. Same deal again, got the router IP address I was expecting on the laptop, but this time I was able to direct traffic to the net. Now the only thing I had changed was the login name and password – NOTHING ELSE.

Swapped it back and it had stopped working again?

I have now exchanged several messages with support and finally I have found someone useful who is willing to help me (even though we are not resolved yet)!!!

They have even changed my block of four but still nothing.

Interestingly I checked my usage through the PN portal, bizarrely is shows significant usage, 800 megabytes for today and nothing has been connected to the line at all since 5pm yesterday!!!

If any one can throw some ideas in, they would be welcome.

Regards

Chris
oliverb
Grafter
Posts: 606
Registered: 02-08-2007

Any one using an ADSL modem in bridged mode?

With a block things change slightly.

Now there's no need for the router to have a private IP at all as the router gets one address from the block and the firewall gets the other usable address. The firewall has it's gateway set to the router's public IP address.
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Any one using an ADSL modem in bridged mode?

Our company uses zoom x4 modems in bridge mode with watchguard fireboxes acting as the firewall and we have no problems - excepting defective equipment etc.

It is all about making sure the watchguard is configured properly.

The modem is in bridged mode simply to route traffic. you should not have to specify nat. Bridged mode infers the modem is invisible hence it all goes through the firebox.

It is all about setting your router in bridged mode simple as. I would investigate the settings for you but I am on the bow preparing for a mates wedding tomorrow!!! Good luck!