Geekzone: technology news, blogs, forums
Guest
Welcome Guest.
You haven't logged in yet. If you don't have an account you can register now.


297 posts

Ultimate Geek

Trusted

Topic # 31159 6-Mar-2009 23:57
Send private message

Hey GZers.

Ok so i've moved to a new place and which has Telecom dsl. They are using the supplied ST modem which is working fine. They also have a belkin router, which is not so good. So i've bought a nice shiny Asus router and put DD-WRT v24 on it and its all set up fine and dandy.

Now, to avoid double NAT and make things a little nicer and faster I want to half-bridge the modem to the router.

On the ST it gives you the option to assign the public IP to a device. Great. When I do that to the belkin router it works fine. Belkin picks up the WAN IP and gateway/dns etc and works a treat (within the belkins limitations of not being an overly good router). As a bonus it also seems to keep a route to the modem so i dont have to fiddle around changing IP addresses if i need to access the modem. Yee har!

However, switch it for the DD-WRT (and reassign the WAN IP to it in the ST) and houston we have a problem. It picks up the addresses fine via DHCP, shows the same address details as in the beklin, but it wont route anything to the WAN, and also wont route to the ST anymore. If i run a traceroute it just seems to loop in the router a couple of times then end.

If i use it without half bridging it works fine, but obviously that means double NAT.

Yes I have the modems/routers on different subnets (have the modem at 192.168.1.0/24 and the router on 192.168.3.0/24.

The only thing I can see which might put a stick in the works is that the upstream Telecom router is in 125.237.255.0/24 but my IP is in 222.154.182.0/24 - how that works is beyong my network skill but anyhoo that seems to be the deal.

So my guess is that DD-WRT maybe can't hack its WAN interface and gateway being on a different subnet? Yet the belkin can?

I might try a linksys AM300 instead, because this guy had more luck with it. Pity I just sent the one I had up to my dad last week.

Otherwise, any suggestions?

Create new topic
Minimalist
5487 posts

Uber Geek
+1 received by user: 415

Moderator
Trusted
Lifetime subscriber

  Reply # 199703 7-Mar-2009 00:26
Send private message

mushion22: . . . Otherwise, any suggestions?

1) Buy an integrated ADSL modem router

2) Buy a modem that can do it's end of the half-bridging better


EDIT: For point 2) see here

(and)
So my guess is that DD-WRT maybe can't hack its WAN interface and gateway being on a different subnet? Yet the belkin can?


I might try a linksys AM300 instead, because this guy had more luck with it. Pity I just sent the one I had up to my dad last week.

If your guess is right, the AM300 won't make any difference as you are going to DD-WRT it with the same version, correct?



297 posts

Ultimate Geek

Trusted

  Reply # 199705 7-Mar-2009 01:01
Send private message

Probably, but that guy said that when using the AM300 it changed the gateway address to be in the same subnet.

So i've just been fiddling some more and but now its changed: my IP address and gateway addresses have jumped into the 122.0.0.0/8 and 125.0.0.0/8 ranges respectively, and my IP subnet is now /16.

Also it seems that DD-WRT isn't adding a default route. It picks up the gateway address but refuses to add a route to it, and even if i try put in a static route it wont add it to its routing table ><.

8027 posts

Uber Geek
+1 received by user: 387

Trusted
Subscriber

  Reply # 199707 7-Mar-2009 01:38
Send private message

What model is the Asus, you might be able to run Tomato on it.  Tomato > DD-WRT imo.

www.polarcloud.com/tomato

I have a Dynalink RTA1320 in half bridge to a WRT54GL running tomato on Telstra PDQ. the ISP gateway address is on a different range/subnet to the WAN IP assigned to the modem and it's working fine.  I can also get to the Dynalink web ui via it's lan ip.  I also have a AM300 that I used to use (the Dynalink syncs higher) which also worked for general traffic but I could never access it via it's LAN ip with the half bridge setup.




297 posts

Ultimate Geek

Trusted

  Reply # 199744 7-Mar-2009 12:33
Send private message

Yeah I looked at Tomato but I think DD-WRT has more features that are useful to me.

I got it sorted anyway. Posted on the DD-WRT forums and was pointed to http://www.dd-wrt.com/phpBB2/viewtopic.php?p=271341#271341 which has worked a treat.

Cheers

8027 posts

Uber Geek
+1 received by user: 387

Trusted
Subscriber

  Reply # 199796 7-Mar-2009 19:29
Send private message

mushion22: ..but I think DD-WRT has more features that are useful to me.


Like which features?



1383 posts

Uber Geek
+1 received by user: 168

Trusted

  Reply # 200610 11-Mar-2009 13:54
Send private message

Mushion22,

I don't think there is an issue with DD-WRT due to the IP & Gateway being in different subnets.  There was a similar issue with the AM300 last year until Linksys did a firmware update for it, however, in the AM300's case it was not correctly passing the gateway address to DD-WRT.  I have an AM300 and DD-WRT running on a Linksys WRT54GL connecting to X-Net (who use a gateway on a different subnet to the IP) with no problems now.

I think that there are subtle differences between how different vendors implement half-bridging, so that could be the issue - vendor compatibility problems.

The only other thing I could suggest is to turn off the firewall on the belkin and see if that makes any difference.

Sam.



297 posts

Ultimate Geek

Trusted

  Reply # 200612 11-Mar-2009 14:10
Send private message

There is an issue if the modem presents the gateway via DHCP as being in a different subnet unless you have a firewall script set to edit the gateway in DD-WRT.
Yes, different modems present it differently. The Thomson we have passes the gateway via DHCP unmodified. As far as I'm aware the AM300 spoofs it to be in the same subnet as the WAN IP. 
The issue is to do with the ISP actually only giving a Point to Point connection rather than access to a subnet. Eventhing gets forwarded onto the ISP router which does some smart logic unlike a traditional network where a machine can send packets directly to other machines on it's subnet. DD-WRT is linux based, and linux implements IP to spec, where as some other platforms can handle it (either intentially or coincidentally) because they are less fussy.
Not sure what the belkin has to do with it other than that it handled the issue fine. I'm not using them simultaneously - am replacing the belkin with the dd-wrt on an asus box.
Its working fine now that I added that script in which checks the subnets of the WAN IP and gateway, and modifies the gateway address if necessary.
Now I just have the problem of my flatmates leaving the default xtra username/pwd set in the modem which expired at midnight last night! ><

1383 posts

Uber Geek
+1 received by user: 168

Trusted

  Reply # 200725 11-Mar-2009 21:25
Send private message

Huh!  I never noticed that the gateway on my DD-WRT router was different to what the AM300 picked up!

Consider me educated! : )

Create new topic

Twitter »

Follow us to receive Twitter updates when new discussions are posted in our forums:



Follow us to receive Twitter updates when news items and blogs are posted in our frontpage:



Follow us to receive Twitter updates when tech item prices are listed in our price comparison site:



Geekzone Live »

Try automatic live updates from Geekzone directly in your browser, without refreshing the page, with Geekzone Live now.



Are you subscribed to our RSS feed? You can download the latest headlines and summaries from our stories directly to your computer or smartphone by using a feed reader.

Alternatively, you can receive a daily email with Geekzone updates.