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6.1.2. Map-Request Message Format

6.1.2. Map-Request Message Format​

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Type=1 |A|M|P|S|p|s|    Reserved     |   IRC   | Record Count  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Nonce . . .                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         . . . Nonce                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         Source-EID-AFI        |   Source EID Address  ...     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         ITR-RLOC-AFI 1        |    ITR-RLOC Address 1  ...    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                              ...                              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         ITR-RLOC-AFI n        |    ITR-RLOC Address n  ...    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |   Reserved    | EID mask-len  |        EID-Prefix-AFI         |
   Rec +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |                       EID-Prefix  ...                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                   Map-Reply Record  ...                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Packet field descriptions:

Type: 1 (Map-Request)

A: This is an authoritative bit, which is set to 0 for UDP-based Map-Requests sent by an ITR. It is set to 1 when an ITR wants the destination site to return the Map-Reply rather than the mapping database system.

M: This is the map-data-present bit. When set, it indicates that a Map-Reply Record segment is included in the Map-Request.

P: This is the probe-bit, which indicates that a Map-Request SHOULD be treated as a Locator reachability probe. The receiver SHOULD respond with a Map-Reply with the probe-bit set, indicating that the Map-Reply is a Locator reachability probe reply, with the nonce copied from the Map-Request. See Section 6.3.2 for more details.

S: This is the Solicit-Map-Request (SMR) bit. See Section 6.6.2 for details.

p: This is the PITR bit. This bit is set to 1 when a PITR sends a Map-Request.

s: This is the SMR-invoked bit. This bit is set to 1 when an xTR is sending a Map-Request in response to a received SMR-based Map-Request.

Reserved: This field MUST be set to 0 on transmit and MUST be ignored on receipt.

IRC: This 5-bit field is the ITR-RLOC Count, which encodes the additional number of (ITR-RLOC-AFI, ITR-RLOC Address) fields present in this message. At least one (ITR-RLOC-AFI, ITR-RLOC-Address) pair MUST be encoded. Multiple ITR-RLOC Address fields are used, so a Map-Replier can select which destination address to use for a Map-Reply. The IRC value ranges from 0 to 31. For a value of 0, there is 1 ITR-RLOC address encoded; for a value of 1, there are 2 ITR-RLOC addresses encoded, and so on up to 31, which encodes a total of 32 ITR-RLOC addresses.

Record Count: This is the number of records in this Map-Request message. A record is comprised of the portion of the packet that is labeled Rec above and occurs the number of times equal to Record Count. For this version of the protocol, a receiver MUST accept and process Map-Requests that contain one or more records, but a sender MUST only send Map-Requests containing one record. Support for requesting multiple EIDs in a single Map-Request message will be specified in a future version of the protocol.

Nonce: This is an 8-octet random value created by the sender of the Map-Request. This nonce will be returned in the Map-Reply. The security of the LISP mapping protocol critically depends on the strength of the nonce in the Map-Request message. The nonce SHOULD be generated by a properly seeded pseudo-random (or strong random) source. See [RFC4086] for advice on generating security-sensitive random data.

Source-EID-AFI: This is the address family of the Source EID Address field.

Source EID Address: This is the EID of the source host that originated the packet that caused the Map-Request. When Map-Requests are used for refreshing a Map-Cache entry or for RLOC-Probing, an AFI value 0 is used and this field is of zero length.

ITR-RLOC-AFI: This is the address family of the ITR-RLOC Address field that follows this field.

ITR-RLOC Address: This is used to give the ETR the option of selecting the destination address from any address family for the Map-Reply message. This address MUST be a routable RLOC address of the sender of the Map-Request message.

EID mask-len: This is the mask length for the EID-Prefix.

EID-Prefix-AFI: This is the address family of the EID-Prefix according to [AFI].

EID-Prefix: This prefix is 4 octets for an IPv4 address family and 16 octets for an IPv6 address family. When a Map-Request is sent by an ITR because a data packet is received for a destination where there is no mapping entry, the EID-Prefix is set to the destination IP address of the data packet, and the EID mask-len is set to 32 or 128 for IPv4 or IPv6, respectively. When an xTR wants to query a site about the status of a mapping it already has cached, the EID-Prefix used in the Map-Request has the same mask length as the EID-Prefix returned from the site when it sent a Map-Reply message.

Map-Reply Record: When the M-bit is set, this field is the size of a single "Record" in the Map-Reply format. This Map-Reply record contains the EID-to-RLOC mapping entry associated with the Source EID. This allows the ETR that will receive this Map-Request to cache the data if it chooses to do so.

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