2 routers on the same network

[nicolaj82]

Hi there. I'm about to help a friend adjust his network setup as he is running a modem with an additional router attached. Both have their DHCP server enabled. And the second router is connected through the wan port to ethernet on the primary. Like this: internet->modem->modem ethernet->router wan

I disabled the DHCP server in the router which didn't work. If i'm not mistaken the problem was that it was connected to the wan port and not ethernet on the router, however it was late so i just reverted the settings.

So would this be the correct way to set this up.
Modem is DHCP server, router DHCP server is disabled.
internet->modem->modem ethernet->router ethernet.

The modem uses 192.168 address range. Router uses 10.200 addresses. So setting it up like above, how do i make sure that you can still connect to the router interface, or is that not a problem i need to be concerned about?

 

[thiggins]

When routers are connected as you describe, both can run DHCP servers. The modem's DCHP server doesn't propagate through the second router. If the second router's WAN port is set to obtain its IP address automatically (via DHCP), then the first router will serve IP address only to the router.
You don't need to do anything for a client on the second router's LAN to reach the first router's admin server. If the second router got its IP info via DHCP, the gateway IP will be correct and you just need to use the first router's admin IP.

 

[nicolaj82]

When routers are connected as you describe, both can run DHCP servers. The modem's DCHP server doesn't propagate through the second router. If the second router's WAN port is set to obtain its IP address automatically (via DHCP), then the first router will serve IP address only to the router.
You don't need to do anything for a client on the second router's LAN to reach the first router's admin server. If the second router got its IP info via DHCP, the gateway IP will be correct and you just need to use the first router's admin IP.

Connecting to both as it is now works. And i understand what you're saying that the modem is only giving out one ip to the router. But because they're having issues with the internet performance. Getting port forwards to work properly etc. So my thought was to connect the rounter to the modem through Lan and disable dhcp so the modem could be set to handle port forwarding etc. and hopefully fix some of their issues.
They're having some issues across most of the connected platforms (several computers, phones PS4 and a network printer) with internet not being as stable as would be expected from a vdsl. I'm thinking about blaming the network setup.
Am i in the wrong when thinking that?

 

[ColinTaylor]

Presumably the "modem" is in fact a combined modem/router?

Can you tell us the make and model numbers of both the "modem" and the "router". Is there anything other than the router plugged into the modem?

Can the modem be put into "bridge" mode?

 

[thiggins]

Getting port forwards to work properly etc.

Two routers in series creates a double-NAT configuration, which will cause problems with port forwarding. This is due to the two firewalls, one in each router.

One solution is to put the internet-facing router in bridge mode. This disables the routing function. Another way to go is to put the second router's WAN IP address in the first router's DMZ. This should open all ports to that router. You would then create port forwards in the second router.

This method may not work in all cases. It depends on the services you are trying to access and the DMZ implementation on the router. But it's worth a shot if you can't put the first router in bridge mode.

 

[nicolaj82]

Two routers in series creates a double-NAT configuration, which will cause problems with port forwarding. This is due to the two firewalls, one in each router.

One solution is to put the internet-facing router in bridge mode. This disables the routing function. Another way to go is to put the second router's WAN IP address in the first router's DMZ. This should open all ports to that router. You would then create port forwards in the second router.

This method may not work in all cases. It depends on the services you are trying to access and the DMZ implementation on the router. But it's worth a shot if you can't put the first router in bridge mode.

The internet facing router does not have this function, you can disable the DHCP server, but there's no option to choose what kind of operating mode you'd like. The first router does have a DMZ function, but using the second routers IP did not appear to work.
This is why i'm think i'll disable the dhcp server in the second router. Would NAT still be enabled if dhcp is disabled, or would i also disable that?

 

[thiggins]

Your problem with port forwarding isn't DHCP servers. It's the double NAT. DHCP from the first router won't make it through the second one's firewall.

 

[nicolaj82]

Your problem with port forwarding isn't DHCP servers. It's the double NAT. DHCP from the first router won't make it through the second one's firewall.

So disabling NAT and firewall on t he second router is the solution. So far i've understood that disabling the dhcp server on the second router and try setting it up as an accesspoint instead is not the way to go.

 

[thiggins]

So disabling NAT and firewall on t he second router is the solution. So far i've understood that disabling the dhcp server on the second router and try setting it up as an accesspoint instead is not the way to go.

Asked and answered. Please reread my earlier posts.

 

[nicolaj82]

Ok, so appearently you can through the isp order bridgemode for the router, it'll basically flash the router with a firmware that'll make one of the ethernet port into a bridgemode port, and the other 3 will continue working as they do now. It's free to do btw.

 

[yorgi]

Ok, so appearently you can through the isp order bridgemode for the router, it'll basically flash the router with a firmware that'll make one of the ethernet port into a bridgemode port, and the other 3 will continue working as they do now. It's free to do btw.

I would say that there is not a problem with the 2 DHCP servers running as much as the DHCP pool begining and ending of addresses.
You need to make sure that you create in in the DHCP server in IP Pool Starting Address 192.168.1.100 and IP Pool Ending Address 192.168.1.254
this way you have 0-99 for Static IP and the rest for DHCP
if you do not do this you may run into problems as you where saying you where having.
I would also agree to run the modem in bridge mode this way you have only the router doing everything and the modem just supplying internet.