> On Jul 16, 2016, at 12:59 PM, Wade Shearer <[email protected]> wrote:
>
> My house is wired with CAT 5. I have a certain room where a printer can’t be
> seen. If I move the printer to any other room, it can be seen. Computers
> plugged into the same jack can be seen and operate on the network normally. I
> have checked the wires at both ends and everything seems to be in order. I’m
> at a loss as to what the issue could be and what to do next. Any ideas as to
> what would cause this strange behavior?
How are you checking the wires?
It’s possible for the wiring in a connection to be marginal, yet still get a
link. This can induce significant delays in Tx and Rx activity (I’m guessing
this is some sort of DSP-related phenomenon; getting high bitrates out of cheap
unshielded twisted pair wires apparently requires some somewhat fancy
processing at the physical layer) and it could be that the printer has a
not-so-great PHY in it. I’ve measured this before with NICs equipped with
precise timestamping hardware for IEEE 1588 (Precision Time Protocol) use. We
thought we had a software bug because we were getting huge peer propagation
delay numbers, but it turned out to be a marginal cable.
It’s also possible that the printer uses some old WizNET ethernet module with
an embedded TCP/IP stack. Some of these aren’t Auto-MDIX capable, while almost
all computer NICs are. If the printer doesn’t get a link while the computers
do, it could be that the transmit/receive pairs are switched when they
shouldn’t be. This seems unlikely, but worth checking out.
Now, if it really isn’t the wires, then we need to look at some higher-level
possibilities.
Can you check the link status and network stack config from the printer front
panel? Is it configured to use DHCP or to use a static IP address? If it uses
DHCP, can you tell if it’s successful at getting a lease? If it can’t get a
lease, can you look at logs from the network DHCP server? Does the printer
have a lease? Is its attempt to get an address visible in the logs? If it is
not answered, is there any indication why? Is there another device that might
be running a DHCP server that could be answering more quickly when the printer
is in that room? If it uses a static address, does it communicate at all as it
boots up, or does it wait passively? Can you switch it to DHCP mode? Does it do
Zeroconf mDNS advertisement?
Are you using a managed or unmanaged switch for the house wiring? If managed,
connect to its management interface and see if the ARP tables change when the
printer is connected and disconnected. Managed switches can often mirror
traffic to another port; this could be handy to diagnose the traffic going
through a port to see why or where it’s going wrong.
Are there any other network switches in the path between the link in the room
where it’s invisible and where you’re checking for its presence from? What
happens if you add a switch connected to the wall jack in the problem room? If
you plug a laptop or something and the printer into a switch in that room, can
you see any broadcast traffic from the printer from a Wireshark session on the
laptop? Do you have an old Ethernet “hub” device that will let you see all
traffic being forwarded through it on another port?
That’s about all I can think of right now. Good luck, and let us know what you
figure out!
—Levi
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