Two broadband lines/routers on one LAN

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John Gray
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Two broadband lines/routers on one LAN

Post by John Gray »

Quite happily we have two broadband lines on the same LAN, and lots of PCs, printers, etc.
A very approximate diagram of the situation which is causing me problems is

Code: Select all

––––––––––––––––––––––––––––––––––––––––––––––––
| HP Procurve Ethernet switch (100 Mbps ports) |
––––––––––––––––––––––––––––––––––––––––––––––––
|                    |
|––Cisco 600         |
|  router [.254]     |
                     |––Draytek Vigor 2760 router
                        (1 Gbps ports) [.253]
                        –––––––––––––––––––––    
                        |             |
                        |––‘server’   | 
                        |   GW .254   |
                                      |
                                      |––NAS 
                                      |  GW .253
My aim was to enable the server and the NAS to communicate at 1 Gbps using the gigabit ports on the Draytek router, but the server cannot see the rest of the LAN devices, and vice versa.

Would you expect that this should be possible without me having to change the server's default gateway to .253?

I can get it to work without gateway changes by connecting a gigabit switch to one of the 100 Mbps ports on the Procurve, and connecting both the server and the RAS to this intermediate switch.
(I can't test any revision now until next Sunday!)
Last edited by John Gray on 19 Sep 2016, 16:13, edited 1 time in total.
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StuartR
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Re: Two broadband lines/routers on one LAN

Post by StuartR »

The usual approach for this kind of thing is to ensure you only have ONE DHCP server on the network. For example you could configure the Draytek router to only be a router, and to pass all DHCP requests through.
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Re: Two broadband lines/routers on one LAN

Post by John Gray »

I hadn't said anything about DHCP! Both the 'server' and the NAS box are on fixed IPs, .10 and .20 respectively.
The Draytek uses DHCP for the other non-printer, non-switch, non-router devices in the range .100 to .199.
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Re: Two broadband lines/routers on one LAN

Post by StuartR »

So how do these devices get their IP addresses and gateways? They should all be on the same subnet with the same gateway for simplicity.
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Re: Two broadband lines/routers on one LAN

Post by John Gray »

My concern is ONLY with the 'server', and why it cannot be found on the LAN when I plug it into the gigabit port on the Draytek.
All its IP addresses information is set up manually, as is that for the NAS box. All devices are on the same subnet, with mask 255.255.255.0.

Everything else works happily.
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Re: Two broadband lines/routers on one LAN

Post by StuartR »

Please clarify "can't be found". Are you accessing it by name or by IP address? Where is the name translating happening? What service is being offered? What happens when you try to ping its IP address?

Why not just give them the same gateway address to use?
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Re: Two broadband lines/routers on one LAN

Post by John Gray »

The 'server' cannot be pinged from a PC (GW .253) by name or by IP address when connected to the Draytek port. I have tested the ~20m patch cable with a cable continuity tester.
I don't know the answer to the second question.
Nor what you mean by 'service'.

It has a .254 IP address so that I can test the Cisco-connected line using a website-based speed tester. All other PCs can test the Draytek-connected line on .253.

Are you saying that it will work only if I change the default gateway on the 'server' to .253?
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Re: Two broadband lines/routers on one LAN

Post by StuartR »

John Gray wrote:...Are you saying that it will work only if I change the default gateway on the 'server' to .253?
I suspect that is the case, yes.
Your default gateway must be on the same subnet as you, which means it can be connected to you by a switch, but not by a router.
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Re: Two broadband lines/routers on one LAN

Post by John Gray »

But both routers are on the same subnet! I am using the gigabit ports on the Draytek router as a switch...
Or doesn't that make any difference?!
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Re: Two broadband lines/routers on one LAN

Post by StuartR »

I'm trying to get my head round this setup. If all three devices are acting as switches then your trying to set up a configuration where the path from server to client is different to the path from client to server. That sounds very odd to me. The default gateway that you supply MUST be a router, so how does the device know whether packets are to be switched or routed?
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John Gray
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Re: Two broadband lines/routers on one LAN

Post by John Gray »

The default gateway assigned by DHCP for all devices on the LAN is always .253 (the Draytek router) with the sole exception of the 'server', whose default gateway is .254, the Cisco router.

The NAS box (IP addresses set manually, default gateway is .253) seems to have no problem in being plugged into a gigabyte switch, either the TP-Link one I mentioned earlier [see last para of my original post] or one of the gigabit ports on the Draytek router. The only difference seems to be with the 'server', whose default gateway is .254.

I suspect that I will need to change this to .253 if I want to use the configuration shown in the original diagram, and of course that might still not work!
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Re: Two broadband lines/routers on one LAN

Post by StuartR »

I think that everything on the same subnet should use the same default gateway.
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Re: Two broadband lines/routers on one LAN

Post by John Gray »

OK, will try Sunday. Thanks!
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Re: Two broadband lines/routers on one LAN

Post by John Gray »

I have tried changing the default Gateway to .253, but the 'server' still seems not to be accessible.

About the only thing left is to assume that 'something' is wrong with the gigabit ports I tried on the Draytek 2760 router - not something which seems at all likely...
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