Addressing

To send a datagram you need an address for the destination. A SCION address carries more than an IP address does. It names which network the destination is in, not just a host within an assumed one. Understanding that extra piece is most of what there is to SCION addressing.

The address model

The Internet you know addresses a host by an IP and a port. It has no notion of which network that host belongs to. Routing to the target is the network's problem, decided hop by hop by BGP. SCION makes the network explicit and part of the address.

A SCION network is organized into Isolation Domains (ISDs), each containing Autonomous Systems (ASes). An AS is identified globally by its ISD-AS, written ISD-AS, for example 1-ff00:0:110 (ISD 1, AS ff00:0:110). A full endpoint address then adds the host and port inside that AS:

The ISD-AS names the network. The host and port name the endpoint within it. This is what makes SCION path-aware: because the destination network is named explicitly, the SDK can look up and choose among the paths that lead to it (see Paths and path policies).

Working with addresses in the SDK

The address types live in the sciparse crate, which scion-stack re-exports, so an application that depends only on scion-stack reaches them as scion_stack::sciparse::…. Two types cover almost everything you do:

• IsdAsn identifies an AS. It parses from and displays as the 1-ff00:0:110 form, and exposes the ISD and AS parts.
• ScionSocketIpAddr is the full ISD-AS + host + port endpoint address, the type you pass to send_to and get back from recv_from. It parses from and displays as 1-ff00:0:110,[fd00::1]:443 (an IPv4 host drops the brackets, for example 1-ff00:0:110,192.0.2.1:443).

For the full type surface (accessors, conversions from std::net types, service addresses), see the sciparse reference.

Wildcards

The ISD-AS 0 (all-zero) is the wildcard, available as IsdAsn::WILDCARD. It expresses "any AS", for instance to bind without pinning a specific local AS, or in path-policy matching. It is a match-any value, not a real address to send to.

Where to go next

• Paths and path policies: once you can name a destination AS, this is how the SDK finds and chooses routes to it.
• The ScionStack model: where addressing fits among the stack's responsibilities.