Hi all,

the following is the explanation about source routing given
here

http://www.faqs.org/faqs/cisco-netwo...ection-23.html

Soure routing is an IP option which allows the originator of a packet
to specify what path that packet will take, and what path return packets
sent back to the originator will take. Source routing is useful when the
default route that a connection will take fails or is suboptimal for some
reason, or for network diagnostic purposes.

now can anyone give me examples for this diagnostic purposes or the commonly encountered situations where source routing is used ?

Well, say you have load balance server with a public key installed, then all traffic to and from this server may use that key. That includes as many backend web servers or whatevere else as you need. By routing everything via that load balance server you need only one public key, and not one per backend server.

Source routing is used in MPLS networks to build traffic engineering tunnels. The internal routing protocols will calculate shortest paths as normal, but then you can use traffic engineering tunnels to direct specific traffic via another path, and this is done using source routing.