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2.2. ALTO Server Network API

2.2. ALTO Server Network API​

An ALTO server [RFC5693] is an entity that generates an abstracted network topology and provides it to network-aware applications over a web-service-based API. Example applications are peer-to-peer (P2P) clients or trackers, or Content Distribution Networks (CDNs). The abstracted network topology comes in the form of two maps: a Network Map that specifies allocation of prefixes to Partition Identifiers (PIDs), and a Cost Map that specifies the cost between PIDs listed in the Network Map. For more details, see [RFC7285].

ALTO abstract network topologies can be auto-generated from the physical topology of the underlying network. The generation would typically be based on policies and rules set by the operator. Both prefix and TE data are required: prefix data is required to generate ALTO Network Maps, and TE (topology) data is required to generate ALTO Cost Maps. Prefix data is carried and originated in BGP, and TE data is originated and carried in an IGP. The mechanism defined in this document provides a single interface through which an ALTO server can retrieve all the necessary prefix and network topology data from the underlying network. Note that an ALTO server can use other mechanisms to get network data, for example, peering with multiple IGP and BGP speakers.

The following figure shows how an ALTO server can get network topology information from the underlying network using the mechanism described in this document.

 +--------+
 | Client |<--+
 +--------+   |
              |    ALTO    +--------+     BGP with    +---------+
 +--------+   |  Protocol  |  ALTO  | Link-State NLRI |   BGP   |
 | Client |<--+------------| Server |<----------------| Speaker |
 +--------+   |            |        |                 |         |
              |            +--------+                 +---------+
 +--------+   |
 | Client |<--+
 +--------+

     Figure 3: ALTO Server Using Network Topology Information
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