Odd ping problem

Friday, 24 February 2017

Here's an odd one for you.

I have a Fedora 19 box - GROUCHO - that is the DNS/DHCP/email/...... server 
for one of my LANs

On there I have a home-grown network status monitor which pings a list of IP's 
and monitors the state, reporting anything that goes missing.

The IP address of this host is 10.6.1.1/24

I also have a Centos 7 box - ZEPPO - on the same subnet/VLAN. This box is a 
file/print server.

This box has two IP addresses 10,6.1.3/24 and 10.6.1.101/24

Groucho happily pings Zeppo on the 10.6.1.101 address.

I have now added a USB WiFi dongle to Zeppo and configured it using nmtui. 
This is to put Zeppo onto the WiFi and enable Air Printing from IPads.

All of this works perfectly fine, and no other devices have any issues - 
except groucho.

If the WiFi link is up on Zeppo, Groucho cannot ping it.  If the WiFi link is 
down on Zeppo, Groucho can ping it.  As I say, the WiFi link state doesn not 
affect any other device, Linux or otherwise.

Neither device have firewalling enabled (for this testing) and both devices 
have very simple routing tables. Even when Groucho cannot ping Zeppo, Zeppo 
can still ping Groucho

---------------------------------------------------
[root@zeppo ~]# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         10.6.1.254      0.0.0.0         UG    100    0        0 enp3s0
10.6.1.1        10.6.103.254    255.255.255.255 UGH   600    0        0 
wlp0s26u1u2
10.6.1.3        0.0.0.0         255.255.255.255 UH    100    0        0 enp3s0
10.6.1.101      0.0.0.0         255.255.255.255 UH    100    0        0 enp3s0
10.6.1.254      0.0.0.0         255.255.255.255 UH    100    0        0 enp3s0
10.6.103.0      0.0.0.0         255.255.255.0   U     600    0        0 
wlp0s26u1u2
[root@zeppo ~]# nmcli con up RW54254
Connection successfully activated (D-Bus active 
path: /org/freedesktop/NetworkManager/ActiveConnection/2)
[root@zeppo ~]#

---------------------------------------------------
[root@groucho ~]# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         10.6.1.254      0.0.0.0         UG    0      0        0 p4p1
10.6.1.0        0.0.0.0         255.255.255.0   U     1      0        0 p4p1
169.254.0.0     0.0.0.0         255.255.0.0     U     1002   0        0 p4p1
[root@groucho ~]# ping zeppo
PING zeppo.ringways.co.uk (10.6.1.101) 56(84) bytes of data.
From groucho.ringways.co.uk (10.6.1.1) icmp_seq=1 Destination Host Unreachable
From groucho.ringways.co.uk (10.6.1.1) icmp_seq=2 Destination Host Unreachable
From groucho.ringways.co.uk (10.6.1.1) icmp_seq=3 Destination Host Unreachable
From groucho.ringways.co.uk (10.6.1.1) icmp_seq=4 Destination Host Unreachable
^C
--- zeppo.ringways.co.uk ping statistics ---
5 packets transmitted, 0 received, +4 errors, 100% packet loss, time 4002ms
pipe 4
[root@groucho ~]# 

---------------------------------------------------
[root@zeppo ~]# nmcli con down RW54254
Connection 'RW54254' successfully deactivated (D-Bus active 
path: /org/freedesktop/NetworkManager/ActiveConnection/3)
[root@zeppo ~]# 

---------------------------------------------------
[root@groucho ~]# ping zeppo
PING zeppo.ringways.co.uk (10.6.1.101) 56(84) bytes of data.
64 bytes from zeppo.ringways.co.uk (10.6.1.101): icmp_seq=1 ttl=63 time=0.230 
ms
64 bytes from zeppo.ringways.co.uk (10.6.1.101): icmp_seq=2 ttl=63 time=0.228 
ms
64 bytes from zeppo.ringways.co.uk (10.6.1.101): icmp_seq=3 ttl=63 time=0.229 
ms
64 bytes from zeppo.ringways.co.uk (10.6.1.101): icmp_seq=4 ttl=63 time=0.213 
ms
^C
--- zeppo.ringways.co.uk ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 2999ms
rtt min/avg/max/mdev = 0.213/0.225/0.230/0.007 ms
[root@groucho ~]# 