Interesting discussions going on Makes interesting reading.
So will this work...

Modem:
Dynamic WAN IP
Connection Type 1483 Bridge I/P VC MUx
LAN IP192.168.0.200
DHCP OFF

Router:
LAN IP 192.168.0.1
Subnet Mask 255.255.255.0
DHCP Range 192.168.0.2..199

This puts the modem outside my LAN DHCP range but within the Subnet range.

With this setup will I be able to login to the modem on 192.168.0.200 from a client within the 192.168.0.2..199 range?

Also, out of interest, if I were to set the modem up as above and connect it up in isolation to another PC will I be able to connect to it by setting an IP manualy on the client as there in no DHCP service running?

No not double NAT, but access the management IP of a bridge device

No that would NOT work.

The router would see the requestion for 0.200 and as that is in the range when you apply 255.255.255.0 to the IP block 192.168.0.x it would NOT route the request to the WAN interface.

If the Bridge device is already using an 192.168.0.x address, then can I suggest using a different range for the LAN side of the router, perhaps 172.17.17.x which is so different it will be easier to think about what is happening.

This faffing around is why I dislike bridge type setups.

Thanks MrSaffron, I understand your logic, I think .
At least I can see why the subnet mask of 155.155.155.0 would put the modems IP inside the LAN and so traffic for it wouldn't be routed to the wan port.
As for changing things. I have static IP's setup in the LAN for various servers (multimedia, print etc.) Plus it is working fine at the moment. So I would rather leave the LAN alone and change the modem setup to work with it.
So, I need the modems IP to be outside the subnet to that any traffic for it will be sent to the wan port of the router.
If I just change the subnet mask on my router to match the range 192.168.0..199.
That will put 192.168.0.200 outside and therefore in the wan will it not? Or am I missing the plot completely?
If I'm on the right path is 255.255.255.199 the right subnet mask for this?
My only concern is that that looks very much like my setup at the moment with my LAN/Router being on 192.168.0.1, subnet 255.255.255.0 and my modem being on 192.168.1.1 completely outside the subnet.
But I can't access it from within the LAN. That makes me think I've missed something fundamental??

On another tack, following on from your faffing around statement in paragraph 3 of your post.. If there is another way to skin this rabbit I'm all ears

The Asus router I used was happy with 192.168.1.x range on one side, and 192.168.0.x on the other side of the router, so don't think that is the issue.

It is more down to the bridge modem, some will only make their LAN IP interface visible to the same device that requested the WAN IP address. So for doing serious reconfiguration I would unplug the ADSL line, and reboot the bridge device before connecting direct to a PC. Then do the reboot before putting a router in the way.

One additional thing that would sometimes help is setting the PC up with manual IP addressing when connected direct to the bridge device.

In short your subnet masks of 255.255.255.0 and 192.168.1.x and 192.168.0.x appear fine.

As the way of avoiding this - use an all in one modem/router. If the reason for the AC router is the high speed wireless then configure that to run as a wireless access point. the RT-N66U I had certainly has that option and works well in that mode

I suspect the the 192.168.x.y IP of the bridge device won't be in the routing table of the ASUS router (even on its WAN side).

Instead of looking for it on the "directly-connected" network of the WAN interface - which being a public IP won't be in the same subnet - it will be looking on the default route (next router at ISP).
(or just dropping it because it's private).

If someone has a router where they can add an IP alias (in the right subnet) to the WAN interface (something more advanced like pfSense would allow that) it might work, but would be impressed if the ASUS has this option?

Edit I'm pretty sure it makes a difference depending if the router is using PPPoE to access the internet via the next device. In this case some routers can talk to the internet via PPPoE but also talk to local (WAN) network at the same time
(if under the hood if ethn and pppn are treated as separate logical interfaces so it can route differently).

Edited by prlzx (Mon 03-Dec-12 20:38:38)

In reply to a post by MHC:

With the BT 2700 hub running in bridge mode it sets an IP address of 192.168.1.254.

Is that a preset fact with it? i.e. it will always set that IP address regardless of what I set?

In reply to a post by MHC:

In your case you are using 192.168.1.1 and 192.168.0.xxx - can you change you LAN addressing to use the 192.168.1.xxx range, selecting say .111 for the ASUS and the DHCP allocatable block at 192.168.1.160 to 200. You will then be able to access the Voyager.

If you are assuming/saying that the bridge will have a local IP of 192.168.1.254 I cabn see the logic as it's outside the DHCP range so the ASUS will pass it to the WAN port but whats the difference between that and what I have already? i.e LAN/Router on 192.168.0.1..255 and Modem on 192.168.1.1 which is definitly outside the LAN segment and I can't access it from within the LAN.
Sorry but I'm getting confused.

In reply to a post by prlzx:

I suspect the the 192.168.x.y IP of the bridge device won't be in the routing table of the ASUS router (even on its WAN side).

Instead of looking for it on the "directly-connected" network of the WAN interface - which being a public IP won't be in the same subnet - it will be looking on the default route (next router at ISP).
(or just dropping it because it's private).

If someone has a router where they can add an IP alias (in the right subnet) to the WAN interface (something more advanced like pfSense would allow that) it might work, but would be impressed if the ASUS has this option?

I see your logic. Pretty sure the Asus doesn't have the capability of your workaround and not sure I do either

In reply to a post by MrSaffron:

The Asus router I used was happy with 192.168.1.x range on one side, and 192.168.0.x on the other side of the router, so don't think that is the issue.

It is more down to the bridge modem, some will only make their LAN IP interface visible to the same device that requested the WAN IP address. So for doing serious reconfiguration I would unplug the ADSL line, and reboot the bridge device before connecting direct to a PC. Then do the reboot before putting a router in the way.

One additional thing that would sometimes help is setting the PC up with manual IP addressing when connected direct to the bridge device.

In short your subnet masks of 255.255.255.0 and 192.168.1.x and 192.168.0.x appear fine.

As the way of avoiding this - use an all in one modem/router. If the reason for the AC router is the high speed wireless then configure that to run as a wireless access point. the RT-N66U I had certainly has that option and works well in that mode

Just jumped from an all in one because I thought it would be more flexible and resilient. and to upgrade LAN/WLAN.
So you think my setup may be ok and if I try rebooting in order it may work.
I'll give that a go.
So will be offline for a short while (I hope )

You can run a traceroute (or tracert on Windows) to what you expect the IP of the bridge device to be, and see if it crosses the ASUS router.
If you then see it heading off into the ISP network (or stopping at their customer access router) you'll know it isn't being recognised / answered by the bridge device.

And that could be because the ASUS router already put this WAN traffic inside the PPPoE tunnel instead of looking on the local WAN (if that is how you are setup) - see Edit on above post.

Edited by prlzx (Mon 03-Dec-12 20:50:05)