Wireless can't ping wireless

[Rick Stevens]

On 01/22/2015 05:30 PM, Jim Lewis wrote:
>
>   I just realized that my wireless computers can't ping each other.
> Wireless to wired and vice versa is just fine. The IP addresses (DHCP)
> are all on the same subnet. If I switch to wired the computer can then
> ping a wired or wireless. The computers can all access the Internet at
> any time (either wired or wireless). I did some research and have
> determined the problem might be my router.
>
>    I use a LinkSys E3000 which I have had for a very long time. I checked
> their site and looked at the Release Notes for firmware upgrades. No
> mention of this issue and so I am hesitant to perform it (I did however
> download the latest file). I got into their Live Chat and the guy said
> since the unit is no longer in warranty I would have to pay to get
> assistance. I thought about doing this, but he could not guarantee
> success and the payment is not refundable. I thought that sucked and
> told him so.
>
>   So, does anyone have any ideas about how I might solve this? I am going
> to be rather surprised if the problem is not the router. If it matters
> here is my hardware:
>
> Fedora 14 - wired desktop
> Fedora 20 - wireless laptop
> Fedora 21 - wireless laptop (or wired)
> Fedora 21 - wireless laptop (or wired)
> Ubuntu 12.04.2 LTS - wireless (practically unusable because of Gnome 3)

Are the wired and wireless connections on the same subnet? If so, you
may be having with the routing of packets. Simply yanking out a cable
doesn't guarantee that the default route gets changed (unless you're
using NetworkManager).

Consider: "A" has 192.168.1.10/24 on the wired NIC and 192.168.1.100/24
on the wireless (both NICs on the same subnet). "B" has 192.168.1.11/24
and 192.168.1.101/24 respectively. Now, "A" sends out a ping to "B".
Which NIC does it use? It will use the default route. Odds are that's
the wired NIC. Now, if you pull "A"s cable out, the default route is
still over the wire (unless NetworkManager or you manually change it).
Hence the outgoing ping never gets sent.

So, check the routes. On "A" with the wired cable hooked up, do a

	netstat -rn

as root and look for the line with the "UG" in it. The value under
"Iface" is which NIC is the default one. Now pull one of cables and
repeat the netstat command. See if the route changes to the other NIC.
If it does, you should be able to ping the other nodes. If it doesn't,
you'll need to drop the wireless connection and restart it (or change
the route manually to the other NIC) and try the ping again.

It's always dangerous to have two different physical NICs on the same
subnet because this sort of routing issue can occur. One way around it
is to use the two NICs in a mode 1 (failover) bonded pair. "bond0"
gets the IP and the network system will automatically fail over to the
other NIC if the primary goes down.
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- Rick Stevens, Systems Engineer, AllDigital    ricks at alldigital.com -
- AIM/Skype: therps2        ICQ: 22643734            Yahoo: origrps2 -
-                                                                    -
-       "As for me, I aspire to be the Walmart Greeter in Hell."     -
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