This is an interesting network setup. Probably a bit more confusing than most people who want to get stuff done would have the patience for.
Unless your WiFi-only hosts have an explicit route for 172.16.2/24, they will send packets destined for Ethernet interfaces of dual-homed hosts to the default route, presumably the OpenWRT. The dual-homed host you are pinging (I'll call it "target") does have explicit routes for both networks, so it will respond directly on the WiFi net. Best case scenario, you get a routing loop like this: WiFi host OpenWRT WiFi OpenWRT Ethernet target Ethernet target WiFi WiFi host There are a whole lot of places where this can fail. So it is time to collect some more information. When you are using tcpdump on multi-homed hosts, make sure to specify the interface you want to see packets on with the -i flag. Also, make sure to use the -e flag so you can see MAC addresses. It doesn't sound like the dual-homed hosts need to have IP forwarding enabled. That would be useful if the OpenWRT goes down and you want another way to jump from WiFi to Ethernet after configuring everything to route through a specified host. I'd probably start with turning that off on target and see what changes in the tcpdumps. If you don't mind static routes on your WiFi-only hosts, you could set a host route for target Ethernet via target WiFi. This gets a bit obnoxious to maintain if you have a bunch of dual-homed hosts. The same would be needed on your Ethernet-only hosts to ping WiFi interfaces of dual-homed hosts. This is a very dirty option, I don't recommend it. Good luck! -- Kenny -+---+++-++-++++--+------+-+-++--++--+-+-++--+++-++----+-++-+++---+----+--+----+ On Wed, 2014-10-29 at 20:20 -0700, David Madden wrote: > I ought to know this, or be able to figure it out, but I'm getting > stupid in my old age... > > I have two networks at home: 172.16.2.x/24 (ethernet) and 172.17.2.x/24 > (WiFi). There's an OpenWRT router between them, and also a couple of > Linux boxes with interfaces on both networks. > > My WiFi-only machines can ping any other WiFi interface, either > interface on the router, and machines with only an ethernet interface. > However, they can't ping the ethernet address of the dual-homed machines > (except for the OpenWRT router's ethernet interface). All the > dual-homed machines are set up to forward IP, although they're not set > as anybody's default route. The dual-homed machines can ping anybody, > although of course they use the interface on the appropriate network to > do it. > > When I tcpdump on a dual-homed machine and ping from a WiFi machine to > the ethernet address of the dual-homed box, I see the ping packets > arriving, but no pong packets going back. > > I thought maybe the dual-homed machine was replying from the WiFi > interface (causing ARP problems, maybe?) or sending to their default > router, but I don't see anything like that happening. > > Any other ideas for what to look for? > > Thanks, > _______________________________________________ > dorkbotpdx-blabber mailing list > [email protected] > http://music.columbia.edu/mailman/listinfo/dorkbotpdx-blabber
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