Hi Ralph
On 13/01/19 11:31, Ralph Corderoy wrote:
Hi Tim,
I'll just ask lots of questions in the hope it strikes lucky.
I have a puzzling issue here, in that I can't see a laptop on my
network from my own computer (normally I can ssh into the laptop just
fine). Both are connected via Wifi. The laptop has a static IP.
So both Computer and Laptop are *only* connected by Wi-fi.
Yes.
Computer's
IP address is from the router's DHCP server. The Laptop's IP address is
static. Is that last one done by having the DHCP server always dish out
the same IP address for Laptop's MAC address, or the Laptop has it
configured directly? If the latter, does the DHCP server know to steer
clear of the static addresses when allocating dynamically?
IP addresses are from third machine (server), which is running dhcpd dishing
out addresses to Laptop and Computer. Laptop gets same IP address 192.168.2.8
from its MAC address, Computer gets its from a pool, 192.168.2.205. The DHCP
server pool is well clear of the static IP's.
Can Laptop see Computer, e.g. ping(1), when Computer can't see Laptop?
No.
All devices are on the same IP network, including the network mask?
Yes.
However, I can ssh into a third computer on the network
How is Third connected? Also Wi-fi only? Static or dynamic IP address?
Cabled, static IP 192.168.2.2.
and from there can ping (and ssh into) the laptop.
When Computer SSH's into Third, does w(1) show you've come from the
Computer IP address you expect? Does `arp' show Computer's MAC address
or that of an access point?
w(1) shows 192.168.2.205 as expected.
arp shows the MAC address of Computer, not an access point.
Can Laptop SSH into Third? Ditto above WRT w(1).
Haven't got SSH set up for SSH logins from Laptop to Third, although I expect
it to work as these machines can see each other on the network.
arp lists the laptop HWaddess as incomplete.
There's also ip-neighbour(8) that gives `ip neigh' to show the table,
and allows an entry to be added. When it's not working, you could try
explicitly adding an ARP table entry to Computer for Laptop and see if
that makes it work.
OK, tried
#ip neigh add 192.168.2.8 lladdr 00:24:d2:94:35:16 dev wlp1s0
RTNETLINK answers: File exists
Further tests:
Disconnecting both Computer and Laptop from the access point and then
reconnecting both to a different access point. Now Computer cannot see Laptop
/or/ Third computer. So disconnect Computer again and get physically close to
the access point. Reconnect and now can see both.
Repeat with original access point, ensuring in close proximity. Again can now
see Laptop and Third from Computer.
So looks like a poor Wifi signal on original connect may be a factor.
I have seen something similar previously in terms of getting an IP address from
the DHCP server. I appear to be connected to the network but have no IP address
assigned to Computer. I am using Network Manager of XFCE and suspect that under
weak Wifi conditions I'm only getting a partial connection.
Cheers
Tim
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