Routing Protocols

Routing in the Kernel

The above packet handling will be processed either in slow path or fast path.

In the prerouting chain, the packet will be checked if needs to be routed or locally processed.

Forwarded Packet

1. If destination IP is known and routing is populated, the packet will be given to the Forwarding Chain from the prerouting chain.
2. Then sent to Post Routing and routed to particular interface.
3. This is called fastpath processing where packet will not be lifted to CPU.

Local Processing

1. If any packet needs to handled by local deamon, or by higher protocol/module TCP, DHCP, it will be sent to INPUT.
2. Processed locally and will be sent to Output Chain.
3. Packets which are lifted to CPU will be travel via INPUT and OUTPUT chain.

Read this post to know more about slow path and fast path. 

Why we need routing protocol?

To avoid static routing configuration, we go for routing protocols. So, routes will be learnt via the protocols.

There are more routing protocols such as IS-IS, OSPF, and BGP 

<Will be updated>