network conundrum

I think you cant have to ifaces in the same net

Try netstat -r or route if both interfaces are on

try a traceroute picam0w and I'm shure you go to picam0w via eth0

Juergen

What you get to life is eth0 only.

The network is confused about is to have two network interfaces in the same subnet but with different addresses. Also, there should be only one default route, now you have two. (Excluding advanced routing with iproute2 or bonding the interfaces).

To try again, move eth0 to another subnet and delete its default route.

Yes, thanks, that certainly allows the wlan to work.

However, I now can't use eth0. I feel certain that in the past I've used both interfaces on the same device, albeit not simultaneously. I recall the wired system having prececence over the wireless, such that when the cable is plugged in, the wireless gets disabled, and re-enabled when the cable is removed.

That's what I was unsuccessfully trying to replicate.

In the Windows world it is certainly possible to have both wired and wireless interfaces in the same network. Windows chooses which to use for outbound data, and acceptsd inbound on both. Disconnecting one causes a failover to the other.

If Linux cannot do this, it must be an issue with the networking software, not with the concept itself.

It's possible in Linux with the correct configuration - it's a bit less "Windows chooses" and a bit more fiddling with scripts that run when an interface comes up or goes down.

I'd like to know the correct configuration...

Maybe a search with Google (or your favourite search engine) would help:

q="two network adapters on same subnet linux"

and number one result shows how to do it!

Skimming through it, ISTM there are a couple of things that doesn't address, failover and load balancing (it's ages since I messed with that stuff). Simply setting a default route on both interfaces will leave all outgoing traffic going through the more recently declared one unless the other interface is specified, I think.

Whoa where did failover and load balancing come from? The OP wanted 2 adapters on the same subnet. The link shows how you can do that. Everything else is a deluxe option that is not included in the basic model. You'll be wanting climate control, leather and self-parking for free next!

Failover is just up there ^, from Alan Adams: "Disconnecting one causes a failover to the other."

Load balancing is my contribution: what's the point of having two network interfaces up if you only use one to route out?

"Load balancing" means to me each connection taking a roughly equal and dynamiclly adjusted share of all the traffic. However you could just be routing say YouTube/NetFlix/iPlayer etc over one connection and everything else over the other, that's simple routing not load balancing.

Indeed. You could be running a server on one interface, or connecting to some manner of server, and using the other interface for everything else, but those are specific manual routing choices. That would also complicate the failover scenario.

I think the term missing here is 'routing metrics', which set the precedence of routes. Lower metric = 'cheaper' route. If the lower route goes away, the higher route is used. It's not for load balancing, when the static routing tables are insufficient to decide which outbound route to take.

It's perfectly sensible to have two IPs on the same subnet, you just need to arrange it so that at all times one route to the subnet (ie 192.168.1.*) has priority.

Plus you need a default route via a gateway (which will use the aforementioned subnet route to work out how to get to the gateway). You can in principle use two default routes to different gateways selected via metrics. This might come in handy if you had, say, a DSL connection and a

Theo

I required it and googled to find if a negative number is also allowed (because I saw that the network route to an interface is created at metric 0 and cannot be undercut except bij negative numbers), and then I read that it is no longer supported in current kernels. There are also other fields (Ref, Use) in the route output that used to be nonzero but have been always zero for a long time now.

(there also used to be a separate "route cache", also gone)

Thanks, Theo.

As the OP, I was severely disappointed at the range of responses so far, ranging from "you can't do that" to "it's difficult" to waffle irrelevant to my question.

Your post has pointed me in the right direction, and a quick google for 'routing metrics' has revealed all sorts of useful and relevant information about my problem. I think I'm now able to set up a system with two interfaces on different addresses.

Thanks again, Tony

What, the free suggestions are not good enough? I'd complain to the net-police that you are not getting the quality of free help you believe you are entitled to.

;-)