RAP, Internet Route Access Protocol

Protocol suite:	TCP/IP.
Protocol type:	Application layer open distance vector routing protocol.
Multicast addresses:
Ports:	38 (TCP, UDP).
URI:
MIME subtype:
SNMP MIBs:
Working groups:
Links:

RFC 1476:

RAP operates on TCP with peers opening a symmetric TCP connection between the RAP ports on each system. Thus only one RAP connection exists between any pair of peers.

RAP is also used on UDP as a peer discovery method. Hosts (i.e., non-routing systems) may listen to RAP datagrams on this port to discover local gateways. This is in addition to, or in lieu of, an Internet Standard gateway discovery protocol, which does not exist at this writing.

The peers then use RAP commands to send each other all routes available though the sending peer. This occurs as a full-duplex (i.e., simultaneous) exchange of information, with no acknowledgement of individual commands.

Once the initial exchange has been completed, the peers send only updates to routes, new routes, and purge commands to delete routes previously offered.

When the connection is broken, each system purges all routes that had been offered by the peer.

MAC header

IP header

TCP header

RAP header

Data :::

RAP header, TCP.

00	01	02	03	04	05	06	07	08	09	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
Length
Version																Command
Data :::

Length. 32 bits, unsigned. 8 to ?.
The offset in bytes from the first byte of the length field of this command packet to the start of the length field of the next. There is no specific limit to the length of a command packet; implementations MUST be able to at least count and skip over a packet that is too large and then MAY send an error indication. Each version of the protocol will profile what size should be considered the limit for senders, and what (larger) size should be considered by receivers to mean that the connection is insane: either unsynchronized or worse. For version 1 of the protocol, senders MUST NOT send command packets greater than 16384 bytes. Receivers SHOULD consider packets that appear to be greater than 162144 bytes in length to be an indication of an unrecoverable error. Note that these limits probably will not be approached in normal operation of version 1 of the protocol; receivers may reasonably decline to use routes described by 16K bytes of metrics and policy. But even the most memory-restricted implementation MUST be able to skip such a command packet.

Version. 16 bits.
RAP protocol version.

Command. 16 bits.