Home Network Issues

Peter Corlett abuse at cabal.org.uk
Sun Sep 9 14:24:48 BST 2012

On 9 Sep 2012, at 13:34, Dave Cross wrote:
>  $ ping
>  PING ( 56(84) bytes of data.
>  From icmp_seq=1 Destination Host Unreachable
>  From icmp_seq=2 Destination Host Unreachable

What host is The one you're pinging from?

Run "arp -a" (you may need to be root) to have a look at the ARP tables. It should show something like this:
# arp -a
? ( at <incomplete> on eth0
? ( at e8:06:88:79:93:ef [ether] on eth0
? ( at 40:3c:fc:04:07:5a [ether] on eth0

ARP is a broadcast protocol for discovering the MAC address of the Ethernet device for a given IP address, and that command dumps the table. In that example, I pinged which doesn't exist on my network, so nothing responded to the ARP request and it shows as <incomplete>. The other addresses do exist, and you can see the MAC addresses. You should also see your default gateway's MAC address (probably or perhaps, or you wouldn't be able to connect to the Internet at all.

Your router may well be filtering ARP requests, even between switch ports. This shouldn't happen on a real switch, but perhaps the SOC has multiple Ethernet ports on it and it was cheaper to implement a switch in software and somebody cocked it up.

If the software really is that bad, it's probably best to treat it as highly suspect and turn off as much as possible, then drop a £40 "broadband router" in front of it. These aren't generally much better - they contain software, after all - but at least the Netgear one I use for this exact purpose has a hardware switch and Wifi bridge between its ports marked "LAN", and I ignore the port marked "Internet" that the software mangles.

Or you can use a dumb switch - I have one free to a good home here - and plug a standalone access point such as an Apple Airport into it. (The Airport does cost twice as much as the Netgear, but it's not just because it's got an Apple badge on it. It really is a much better access point.)

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