Odd LAN setup

[TechnoPro]

A client of mine showed me his home LAN setup and it was a bit odd.

His cable modem was conencted to a 5 port switch. The switch connected off to the WAN port of 2 different routers. Diagram, as follows:

Cable modem -> Switch -> Router (Netgear)
. . . . . . . . . . . . . . . . . . . . . . . -> Router (Linksys)

His logic was to ensure that the PC connected to one router would be completely inaccesible to the PC connected to the other. Is this thinking correct? If he had higher end equipment, he could simply set up a VLAN, correct?

EDIT:

Thanks to VeXeD for pointing out my glaring typo. The switch is connected to the WAN port of each router.

 

[nweaver]

they must have 2 external IP's to do this. It does what they need. It would be rough to do this with only a managed switch, you would have to do router on a stick with a decent (i.e. not SOHO) router. This solution looks like an easy fix to me.

 

[TechnoPro]

Originally posted by: nweaver
they must have 2 external IP's to do this. It does what they need. It would be rough to do this with only a managed switch, you would have to do router on a stick with a decent (i.e. not SOHO) router. This solution looks like an easy fix to me.

That's the kicker. They do NOT have 2 external IPs! Next time I am onsite, I want to see what IP's each router is given...

 

[Genx87]

What kind of switch is it?

 

[TechnoPro]

Originally posted by: Genx87
What kind of switch is it?

Linksys, 5 port.

 

[Slowlearner]

The routers are also switches so the whole thing should work like a single network - which isnt what he wanted.

 

[amdskip]

Are you sure it wasn't 3 routers?

 

[VeXeD]

Originally posted by: TechnoPro
His cable modem was conencted to a 5 port switch. The switch connected off to the LAN port of 2 different routers

You mean the switch connects to the WAN ports of both routers, correct.

If so what nweaver said would be correct.

 

[TechnoPro]

Originally posted by: VeXeD

Originally posted by: TechnoPro
His cable modem was conencted to a 5 port switch. The switch connected off to the LAN port of 2 different routers

You mean the switch connects to the WAN ports of both routers, correct.

If so what nweaver said would be correct.

Yes, the WAN port. Major typo on my part.

 

[TechnoPro]

Originally posted by: Slowlearner
The routers are also switches so the whole thing should work like a single network - which isnt what he wanted.

Due to manufacturer variation each router is indeed on a different subnet. The netgear default router IP is 192.168.0.1, versus the Linksys which is 192.168.1.1. Should he have coincidentally purchased equipment from the same vendor, well...

I wasn't concerned with having 2 DHCP servers running since the DHCP requests would not cross the router being broadcast traffic.

 

[TechnoPro]

Originally posted by: amdskip
Are you sure it wasn't 3 routers?

Very sure.

 

[Sketcher]

Ditch the switch:

Modem <- RouterA <- RouterB

Assign a different subnet & IP range for RouterB to dish out and you have the separation you're looking for. In your case, you state that the default configs of each unit ARE already separate. Then you just need to position them as noted above.

Example:

RouterA dishes out 192.168.1.xxx
RouterB dishes out 192.168.2.xxx

A computer receiving DHCP from RouterA will be on a different subnet than a computer receiving DHCP from RouterB.

RouterB is getting it's WAN IP from RouterA which is configured to reach the internet via the modem. Computers on both router subnets reach internet but can't see each other (unless routing tables are configured to allow it).