The IDRP Protocol

The Inter-Domain Routeing Protocol (IDRP) is an exterior routing protocol used for exchanging routing information between autonomous systems. IDRP is used for exchange of routing information between multiple transit autonomous systems as well as between transit and stub autonomous systems. IDRP is related to EGP but operates with more capability, greater flexibility, and less required bandwidth. IDRP uses path attributes . to provide more information about each route. Path attributes may take administrative preferences based on political, organizational, or security issues into consideration in the routing decision. These attributes allow much more flexibility in determining route preference for administrative reasons instead of just computed costs.

IDRP created from both ISO standards bodies and IETF IETF . standards body. IDRP is equivalent to a multi-protocol version of BGP.

IDRP vs an IGP protocol such RIP

Unlike interior protocols, in IDRP metrics do not play a primary role in determining the best route. The IDRP metric is an arbitrary 16-bit value that can be used as one criterion for choosing a route.

IDRP Configuration Syntax

Overview MERIT IDRP implementation

The IDRP protocol supports two basic types of routing information, internal (also known as IIDRP) and external. External routing information is received from other autonomous system, while internal information is received from other border routers within the same autonomous system. For external advertisements, the Routing Domain Identifier is prepended to the RD path before advertisement. For internal advertisements it is not prepended.

IDRP collects both reachability announcements received during the processing a input packets and transmits it to its peers. IDRP uses a 3 phase processing approach to the processing of routes and policy. After an IDRP BISPDU is receieved, the phase 1 processing sends all the routes to internal neighbors. Normal Gated task processing sends only active routes to neighbors. The IDRP receive packet (idrp_recv) code has been setup to send all routes to internal neighors during the input packet processing and intial installation into the routing task.

This approach does not fit into the standard gated internal processing model. The standard gated processing only sends active routes to peers, and not "all routes" inputted from a particular type of peer. IDRP does this phase 1 processing during the processing of an incoming pdu prior to returning control to gated. A longer than normal processing time may be encounter due to this change in the logic.

IDRP Phase 2 processing occurs as gated selects the active route. The IDRP phase 1 processing IDRP provides the tie-breaking information between two IDRP routes. The tie-breaking information is calculated during phase 1.

For routes sent to a neighbor (in phase 1 or phase 3), the maximum amount of routes are packed within an UPDATE BISPDU. Each group of routes sent to a peer, is then tagged with a route-id . To delete routes, a IDRP peer must remove routes by route-id.

For a strict implementation of the IDRP protocol, all routes received from external peers must be sent to all internal peers. For the phase 1 processing the route will be sent if export policy restricts the transmission of the route.

After gated selects the active routes, IDRP will process both static and IDRP routes based on a per peer status, all routes eligble to to be sent to A copy of the message is sent to every peer in the group, with possible adjustments to the next hop field as appropriate to each peer. This minimizes the computational load of running large numbers of peers in these types of groups. BGP allows unconfigured peers to connect if an appropriate group has been configured with an allow clause.