A strange issue I noticed lately.
I am trying to ping an android tablet (Lenovo Thinkpad Tablet) which is in the same LAN
as the PC. While the PC is connected via ethernet the android tablet is via wireless.
What I noticed is that pinging from PC i get a “destination host unreachable” for a long time,
may be 5 min or less, didn’t keep time on that.
Pinging the same tablet at the same moment from the RB750 I get 3 time-out and then ping goes
normal.
I want to understand what is going on.
My guess is that router does remember the mac address of the tablet and knows where to send
the icmp request, while the PC does not know, and so the switch and the access point where the tablet
is connected. I also think that the tablet is not broadcasting to save battery, so it is not advertising itself
in the domain.
What do you think?
As a test I added another IP on the LAN interface of the router and assigned the PC to the new address space,
say tablet IP=192.168.1.100 and PC IP=192.168.10.100, so that when the PC sends a request for the tablet IP
it is forced to go through router instead of looking for it in the network. This way it works very well.
I have noticed that power saving routines on Android are EXTREMELY aggressive, sometimes turning the wireless ckt. on/off multiple times in a 5 sec. time frame. This might affect things.
I haven’t found a way to force it ALWAYS ON, but a Google search might turn up something.
Yes, it is true that they apply aggressive modes to save energy. But anyway, this was not the point.
I am more curious on a network stand point of view. While the router is capable of reaching the device
after 3 time outs of the ping, the PC can not.
I am just suggesting that it could be the power saving switching off the Android wireless hardware that is causing the problem.
I know that logically, since the router can reach it you would think this would not be the case, but it would be good to rule it out before spending a bunch of time researching other stuff.
If it doesn’t work from a wired client to the wireless client but it does from the router itself, you may want to look at your bridging. If you’re coming in on ether2 and trying to go out the bridge interface or wlan1 interface, make sure you have the appropriate rules and the bridging is setup properly.
Where “AP” is a cheap commercial access point. Because of the behavior I have a feeling
that is mostly related to the broadcast packets. I think that the Tablet while in sleep mode
does not advertise itself in the network, this way it can save power. The tablet will only check
for internet once in 5 min for example, and this is the moment when the PC can find it.
This is my guess, but I am not that good on how packets and broadcast work. That’s why asking
