Strong host routing

Strong host routing is an interesting concept. This is of interest in multi-homed ( having two or more network addresses) hosts. How to route a given packet to the network is done not only based on the "destination address", but also based on the "source address". Strong host model is mentioned in RFC 1122. This adds more security as packets cannot be sent out with a source address that does not belong to an interface in the host.

On Receive side,when a unicast packet arrives at a host, a weak host model will accept the packet if the destination address matches any of the local IP addresses of the host. But in strong host model it will accept the packet only if destination address matches the IP address of the interface in which it receives. It thus prevents any multi-home based network attacks.

Net Generation TCP/IP stack in Microsoft Vista supports strong host routing by default.

TCP/IP socket - in a multi-homed host

In a multi-homed host ( host having two more network addresses), how does a TCP/IP socket connection behave ?

How does it find the interface through which packet has to be forwarded ? It depends on the entries in the forward information table.. ( or route table - ).. if there are more than one interface to the same destination it looks for the lowest Metric value.. or if it does not find an entry it forwards through the default route gateway interface..

Then how does it determines through which interface it should listen for the reply ? If "bind" is not explicitly called, the TCP/IP socket will listen on the interface through which the packet was forwarded..!

Using "bind" before "connect", we can explicitly bind a interface, if needed..