On 30 April 2015 at 09:37, Chris Green cl@isbd.net wrote:
However, at this point I fail to see what difference it makes compared with simply having all the devices on the same subnet. You just have the added complication of having to setup the IP aliases on the single network card.
I'm sure we're talking at cross purposes here.
The "standard" option for making use of multiple WAN connections, as implemented in (eg) a Draytek router, is that (a) each WAN connection is a distinct physical port (on my Draytek that's an ADSL port, a standard network port and a USB port for a 3G dongle), (b) each interface is on a different subnet, (c) the LAN is connected to separate LAN port(s), utilising the router as the default gateway, (d) the router routes traffic out of whichever WAN port it decides is most appropriate based on load, failover, any specific defined rules, etc.
The only question I'm trying to answer here is why doea this setup require different physical ports on separate networks, rather than virtual ports on the same network.
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.
Yes, but, as I say above, what have you gained?
Er, what I just listed? If I want to set up a router using (eg) a Pi, then requiring a physical interface per network makes it a non-starter. Much simpler cabling is a bonus (although not critical).
So there still needs to be some sort of load balancing/decision making in the router which is specified as the gateway for all the connected systems.
Absolutely, that's what the router is for!
I can see no advantage over:-
192.168.1.1 - 'master' router, is the gateway and does DHCP 192.168.1.2 - router A, fixed IP, no DHCP 192.168.1.3 - router B, fixed IP, no DHCP 192.168.1.3 - router C, fixed IP, no DHCP ... ... 192.168.1.x - system(s) assigned IP by master router ...The routing/load balancing algorithm in the master router sends packets out via its own external interface or off to one of the other
Agreed, that was the secondary part of my question (whether all WAN connections needed to be on different subnets). But either way the point is: can any of this work in reality? There is surely a reason why routers expect to have a separate physical port per WAN, when a relatively simple mod would allow multiple WANs to be supported on a single physical interface if the above is true. But if there is such a reason, what is it?