On Wed, 29 Apr 2015 15:39:48 +0100 Mark Rogers mark@more-solutions.co.uk allegedly wrote:
On 29 April 2015 at 15:09, Chris Green cl@isbd.net wrote:
So what good would this do you? All the routers can talk to each other, the rest of the network can communicate with itself but you have no way to communicate between them.
Why?
Let's say I have three ADSL routers on (respectively) 192.168.1.1, 192.168.2.1, 192.168.3.1, all with 255.255.255.0 subnets and all with DHCP turned off. The LAN ports of all of these could be connected to the same switch and they'd not be able to talk to each other as they're on different subnets. (I've tweaked IP addresses from my last post.)
I then add a new box with one network card (connected to the same switch) but a number of IP addresses on it (eth0=192.168.100.1, eth0:1=192.168.1.2, eth0:2=192.168.2.2, eth0:3=192.168.3.2), so it can talk to everything. Enable DHCP on the 192.168.100.x range.
I then add other PCs and laptops (etc) to the same switch (or via WiFi to the same network) and they all get 192.168.100.x addresses, gateway 192.168.100.1. They can only see the gateway, it can then forward traffic as required to each of the three ADSL routers.
(Aside: My routing knowledge isn't strong enough to answer this, but I can't actually see why this couldn't also work if all the routers and the rest of the network were on the same subnet.)
What advantages would using the same physical network confer?
Reason why this might be useful (and why I was thinking about it): Simpler hardware for the "box" (just one physical interface required so something like a Pi could handle it). Simpler cabling (the ADSL routers don't all need to be in one location and "behind" the "box"). It means that the number of WAN's a router can support is not limited by having to have a separate physical port for each one.
Downside is throughput, although with a gigabit card and several 4Mbps ADSL connections I don't think it's going to be struggling. Other downside might be "but it won't work", which is why I was asking!
I don't really see what is different between having eth0/eth0:1/eth0:2/eth0:3 (on a single cable) vs eth0/eth1/eth2/eth3 (on separate cards but all connected to the same switch) vs eth0-eth3 on separate networks.
... and what/who decides which router to use?
There's only one DHCP server and that would "decide". Of-course any device on the network could be configured to use one of the gateways directly but that's a "feature" rather than a problem in a small network (I accept that there are plenty of environments where you'd want to lock that down though). Even so, managed switches could control that rather than needing separate physical interfaces in the router.
Mark
I think I can see what you are trying to do, but I see a problem. What is your default route to the wider internet?
All you internal systems will have a default route set as 192.168.100.1. But which router does that box choose to send traffic out? You could set up your own routing table partitioning the outside world into three bloody great subnets and allocating one to each of the ADSL routers, but that is asking a lot of your little domestic setup. Alternatively, you have one default route allocated, but I don't see how that helps you since the other two routers then become redundant.
Or have I missed something?
Mick
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Mick Morgan gpg fingerprint: FC23 3338 F664 5E66 876B 72C0 0A1F E60B 5BAD D312 http://baldric.net
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