In SCION the source address of a sending host needs to be known in order to be able to send a packet. The easiest way to achieve this is to explicitly bind a socket to an address other than the wildcard address with scion_bind(). The wildcard address is the IPv4 address 0.0.0.0 or the IPv6 address ::.
In cases where a socket is implicitly or explicitly bound to the wildcard address the library tries automatically determine the source address with different methods. This automatic source address determination makes the following assumption:
in the network (AS) all communication partners (hosts and border routers) can reach the host running CSNET with one and the same address
The source address of a socket is determined as follows:
Note that it is possible for the automatic source address determination to fail (sending will result with a SCION_SRC_ADDR_UNKNOWN error). In such cases, a non-wildcard address has to be bound explicitly.
