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341 posts

Ultimate Geek

# 49267 18-Nov-2009 16:00
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Hi everone, I got a 4 ports ADSL modem/router (TD-8840), but couldn't figure how to properly setup the router part so it will
be able to manage two of my PCs and a wireless router (WRT54G).

Currently my PC directly connected to one of the ports could reach the internet with a statistic IP but could not reach other PC
and I don't think the wireless part is working yet. Anyway, how to set up the Routing--Default Gateway so that my PC's could see each other? I beleive it lies in the Routing sections:
-->Default Gateway
-->Static Route
 And in the first section I have following

Routing -- Default Gateway

If Enable Automatic Assigned Default Gateway checkbox is selected, this router will accept the first received default gateway assignment from one of the PPPoA, PPPoE or MER/DHCP enabled PVC(s). If the checkbox is not selected, enter the static default gateway AND/OR a interface. Click 'Save/Apply' button to save it.

NOTE: If changing the Automatic Assigned Default Gateway from unselected to selected, You must reboot the router to get the automatic assigned default gateway.

Something like:
Enable Automatic Assigned Default Gateway
Use Default Gateway IP Address
Use interface

Which one should I change? I've tried various selections in this part, but they don't work

Or should I configure Static Route part instead?

Routing -- Static Route (A maximum 32 entries can be configured)

Destination Subnet Mask Gateway Interface

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341 posts

Ultimate Geek

  # 274268 18-Nov-2009 16:42
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Well, turn out the router setting was fine, I couldn't connected to another PC because it silently die due to a file system inconsistence caused by a power outage. It is a headless Linux serve, so I have to drag it out of dusty corner and pull out live monitor and keyboard to fix it, seems fine now.

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Uber Geek


  # 274269 18-Nov-2009 16:45
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Wan Bypass Setup

This will use the TD-8840 as the router and dhcp server and the WRT54G as just an access point.  It avoids your connection going through NAT twice and having to foward ports in both devices.

On the TD-8840

1: Unplug the WRT54G from the TD-8840 for now
2: Plug your PC into the TD-8840's switch
3: Login to the TD-8840 admin ui, the default ip address should be
4: Change the DCHP range given out by the device to start from (this is to free up for your WRT54G)
5: Save

On the WRT54G

1: Plug your PC into the WRT54G's switch
2: Login to the admin ui
3: Change the LAN IP address to be, change the LAN gateway to be (the address of the TD-8840)
4: Disable DHCP (all clients will get ip addresses from the TD-8840)
5: Save and reboot
6: Connect a network cable from a lan port on the TD-8840 to a lan port on the WRT54G (don't use the wan port on the WRT54G).

Let us know how it goes.

Note: There is an alternative way to setup the devices (PPoA Half Bridge aka IP Extension) which uses the WRT54G as the router and DHCP server and sets the TD-8840 as just a dumb modem but it's a bit trickier and unless you're running custom third party firmware on your WRT I think you're better off with the TD-8840 doing the heavy lifting.


341 posts

Ultimate Geek

  # 274326 18-Nov-2009 21:06
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Thank you Ragnor, that really helped me to clarified few things. I end up doing almost exactly as you suggested myself. My one is WRT54G V5, and my understanding is it is a skimmed down version of WRT54G and did put third party firmware onto it as the choices are limited and I almost ended up use it as access point.

About the WRT54G part, what's the difference of put cable from TD-8840 to WRT-54G's LAN port or WAN port. My understanding is the latter I will use WRT54G as gateway and router for WiFi. It needs a little bit setting but could reduce the routing job of the TD-8840, and probably provide little bit more speed compare all the traffic go though TD-8840? As there are two PCs almost always online with NFS file sharing. and I always found the WiFi performance are little bit disappointing? Will it improved if I have wireless and wired in different subnet?

8035 posts

Uber Geek


  # 274346 18-Nov-2009 22:46
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The devices that are connected by wireless, are they using they 802.11g (54 Mbit) or 802.11b (10 Mbit)?

The real world throughput of wireless is usually not very good because it's half duplex, no full duplex like communication over a 100Mbit ethernet cable.  Basically wireless can't send and recieve at the same time, it alternates between sending and recieving data.

Real world throughput of 802.11g is around 22 Mbit/s, 802.11b is around 5Mbit/s.

Remember that's bits, there's 8 bits in a byte so 22 Mbit/s is around 2.75 MB/s (megabytes) which is pretty slow compared to 100Mbit (12.5 MB/s)

341 posts

Ultimate Geek

  # 274357 18-Nov-2009 23:11
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It is G only mode in my Wireless router, but still paused occasionally when try to stream video. I think your figure of 2.75MB are more close to my experience than what I thought something like 6-7MB/s Probably boost Wireless signal would helps more than worry about the router load.

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