OSX 10.11 introduced System Integrity Protection feature protecting the /usr/sbin folder, which will break existing miredo functionality to connect teredo tunnels.

Steps to fix it:

1. Copy/move upgrade-migrated miredo command line tools from /Library/SystemMigration/History/Migration-XXX/QuarantineRoot/usr/sbin/ to /usr/local/sbin
2. Edit /Library/LaunchDaemons/miredo.plist to use new /usr/local/sbin/miredo instead of /usr/sbin/miredo
3. Re-enable miredo in prefpane

Since El Capitan also force kernel driver signing, if your tun/tap driver has problem to load, install the latest ones from here.