It's free under the GPL
It provides a modular mechanism to add new protocols as they are developed.
There are other packages, but Zebra addresses limitations in other implementations.
Once process per protocol.
Kernel routing table update and redistribution between different protocols. It is easy to add new protocols because of the API.
Benefits of multiple server:
However, multiple processes can be slow
Benefits of user level routing table
API is not complete.
Each server has a terminal interface that is similar to the Cisco terminal interface. Each server has its own configuration file.
RIPv1 and BGP have been implemented. OSPF has not yet been implemented.
Updates are available at http://zebra.digital-magic.co.jp
What is the thread implementation on the Mach Kernel? There are two mach scheduling mechanisms being used. One uses no scheduling at all. The other schedules only one.