Fixing Internet Sharing DHCP

要約：
OSXのインターネット共有がうまく動かない、特にクライアントがIPアドレスの取得に失敗する場合は、
/Library/Preferences/SystemConfiguration/com.apple.nat.plist を開き、 <SharingNetworkNumberEnd> および <SharingNetworkMask> の項目を確認します。

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After updating to El Capitan, OSX Internet Sharing stopped to work. Especially, it fails to give IP address to clients.
The Console says "DHCP DISCOVER" rather than "DHCP REQUEST".

After careful investigation, I saw

InternetSharing[PID]: missing dhcp parameters: start address 10.*.*.*, end address or mask

After googling, I met a Chinese blog: http://xnow.me/linuxes/custom-os-x-internetsharing-settings.html

It says "Open /Library/Preferences/SystemConfiguration/com.apple.nat.plist and check <SharingNetworkNumberEnd> and <SharingNetworkMask>."
And I recognized my plist did lack the entries. Now I was able to fix the DHCP server (and dump packet via WireShark...)

Tested on: MacBook Air OSX 10.11, sharing EasyTether via Wi-Fi.