Comment 13 for bug 849297

Are you using the same process on both systems?

Note the errors here:
Sep 13 14:16:30 kristopher-LT21 NetworkManager[503]: <info> Executing: /sbin/iptables --table filter --insert FORWARD --destination 10.42.43.0/255.255.255.0 --out-interface eth0 --match state --state ESTABLISHED,RELATED --jump ACCEPT
Sep 13 14:16:30 kristopher-LT21 NetworkManager[503]: <info> Executing: /sbin/iptables --table nat --insert POSTROUTING --source 10.42.43.0/255.255.255.0 --destination ! 10.42.43.0/255.255.255.0 --jump MASQUERADE
Sep 13 14:16:30 kristopher-LT21 NetworkManager[503]: <info> Starting dnsmasq...
Sep 13 14:16:30 kristopher-LT21 NetworkManager[503]: <info> (eth0): device state change: ip-config -> activated (reason 'none') [70 100 0]
Sep 13 14:16:30 kristopher-LT21 NetworkManager[503]: <info> Activation (eth0) successful, device activated.
Sep 13 14:16:30 kristopher-LT21 NetworkManager[503]: <info> Activation (eth0) Stage 5 of 5 (IP Configure Commit) complete.
Sep 13 14:16:30 kristopher-LT21 NetworkManager[503]: <info> Activation (eth0) Stage 4 of 5 (IP4 Configure Get) complete.
Sep 13 14:16:30 kristopher-LT21 NetworkManager[503]: <warn> dnsmasq exited with error: Network access problem (address in use; permissions; etc) (2)
Sep 13 14:16:30 kristopher-LT21 NetworkManager[503]: <info> (eth0): device state change: activated -> failed (reason 'sharing-start-failed') [100 120 18

The last two indicate dnsmasq has failed to start because the IP was already in use. This is likely because on the same link, another system is already configured to share the connection or there is an issue with the network's router configuration.

Please verify your settings or provide additional information as to how your network is configured, how many systems are connected to the wired network (including things behind a switch or router), and how the other systems are configured.

Note that ICS uses the 10.42.43.0 range to setup connection sharing. This is hard-coded.