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Ethernet card won't grab new IP on new network

Occasional problem: when waking up computer at work after its been on the home network, the ethernet card will refuse to grab the new ip from the dns.

From here:

sudo ifconfig en0 down
sudo ifconfig en0 mtu 1500 up

Make sure of your mtu value by doing
ifconfig en0

Result will be of the form

en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
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