Why Linux is blind to this ARP reply 2972

andres box network

snip

The only hard data I have to work with :) :(

The Host Unreachable message means just what it says, the host (10.10.0.46) is unreachable. Host offline, host not on segment that packet was routed to, a blocking rule in effect, or an "indeterminent route" lookup failure are the most likely cause(s).

Several reasons possible: 1) bad route table entry or typo for GW (10.10.0.46) in Linux 2) other subnet(s) entries are "masking" the correct GW route -- side effect of "longest prefix match" rule for choosing route-interface for forwarding. 3) routers are responding to arp but they-something else is blocking ping access -- fairly common in some setups

Can't really guess any further than this without config info asked for earlier. Without the info they provide, it is too dificult to sort out your symptoms-descriptions. If you can't-don't wish to provide such info, that is OK, just say so. In that case I can't help much.

You could try as a "quick-n-dirty" test: -- make host entry for 10.10.0.46 in Linux route table and see if that works. If it works it suggests 1) or 2) above.

Right now I'm favoring (2) the notion that one (or more) of the other subnet entries is interferring with correct route selection, in which case Linux box will just drop the packets without putting anything on the wire. Ie., Linux is getting the arp response from routers, but is unable to form a routable packet from the info, so drops the packets on the floor.

This is a very easy mistake-misconfiguration and very hard to "eyeball" the problem from looking at (quad-decimal) configurations. You have to break down all the net-subnets into binary and double check that prefix-netmask bit boundaries aren't hiding or "masking" correct routes to some subnets-segments.

You might watch the arp cache and see if it is populating with a table entry for the routers (10.10.0.46) and then see what, if anything, shows up in the route cache. You can monitor the route cache in "real" time with: use Ctrl-c to stop it.

This is all I can do to help without the config info ;-(

hth, prg email above disabled