I have been managing our home network now for many years, and this is the weirdest problem I have ever seen:

I have a router (Dlink DIR-655) to which a printer is connected directly via cat5e. The router also provides wireless access. Router has IP, the printer is .0.2. Now if I connect my laptop to the LAN via cat5e, I can ping the printer from laptop, but if I connect the same laptop via wireless (and disconnect its cat5e), it can no longer ping the printer.

Surely it is the laptop, right? Wrong: this happens with all 3 laptops we have the house: connect the laptop via cat5e, it can ping printer, otherwise via wireless it cannot. The laptops are all very different, two are work laptops from different companies, the third is the kids machine.

So surely ping over wireless is disallowed by router! Wrong: each laptop, independent of how it is connected to LAN (wireless or cat5e) can ping the other laptops. This means wired laptop can ping both wired and wireless laptop; wireless laptop can ping both wired and wireless laptop; but only wired laptop can ping printer.

How does this make sense?

  • Can you confirm that a wireless laptop can ping a wired laptop? You seem to say the other direction works, but I care about this direction. – Spiff Dec 1 '13 at 22:18
  • What is the IP address of the laptop? Has the printer been given a fixed IP address, or is it using DHCP? Has the printer been configured correctly for wireless? What model printer? – hdhondt Dec 1 '13 at 22:20
  • @Spiff Yes it can, both connection types work as expected between laptops. I've updated the question (last paragraph). – Oliver Dec 2 '13 at 3:02
  • @hdhondt Over wireless, the laptop is .0.101. Over wired, it is .0.196. The second laptop is .0.198 (over wireless -- have not tried wired for that laptop). The printer is wired only (no wireless) and has static IP (.0.2), whereas the two laptops use DHCP (reserved so always same address). DHCP addresses are in range .0.100 to .0.199. – Oliver Dec 2 '13 at 4:35
  • What does ping -4 give you on WiFi with the laptop? (-4 stands for IPv4) – Rik Dec 2 '13 at 9:45

Thanks for all the comments. Turns out that the problem was a wrong MAC address entry but you might be interested in how that could explain the behavior described in my question, because indeed the printer could be pinged and even printed fine from wired laptops. Turns out that my router supports complete blockage of wireless devices from my LAN by MAC address, but only partial restriction for wired devices. The partial is what I didn't know was a possibility, and I don't know if all routers are like that. The printer MAC address that was in the router's table was that of the old printer, but because of the partial non-restriction, the printer worked fine from wired devices. This bit from the router's documentation explains it:

Note that a wired device that is blocked cannot access the WAN and cannot access wireless devices on the LAN, but can still access other wired devices on the LAN.

That's the part that I was totally not expecting and explains all behavior listed in my question. I really thought I was missing something fundamental about networking so despite the silliness of the mistake, I'm glad as I learnt something.

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