Wireless can't ping wireless

[Jim Lewis]

> 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.
> ----------------------------------------------------------------------
> - 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."     -
> ----------------------------------------------------------------------
>

Hi Rick,

  I do not ever have 2 NICs enabled on the same subnet at the same time.
Whenever I want to switch from wired to wireless, or vice versa, I
always use NetworkManager to disable the current interface first before
enabling the other one. Note too that if this had been a mixed up NIC
problem the laptop would not have been able to ping anything. Wired
always works. I also always check ifconfig for the current IP.

 If I weren't such a wuss I would just go ahead and upgrade the firmware
on my router. That might actually solve the problem. It's currently at
version 1.0.02 and the latest is 1.0.06. However, I have seen these
updates fail so many times (mostly at IBM) I'm too scared to try it.


Jim Lewis