6.1.3. EID-to-RLOC UDP Map-Request Message
6.1.3. EID-to-RLOC UDP Map-Request Message
A Map-Request is sent from an ITR when it needs a mapping for an EID, wants to test an RLOC for reachability, or wants to refresh a mapping before TTL expiration. For the initial case, the destination IP address used for the Map-Request is the data packet's destination address (i.e., the destination EID) that had a mapping cache lookup failure. For the latter two cases, the destination IP address used for the Map-Request is one of the RLOC addresses from the Locator-Set of the Map-Cache entry. The source address is either an IPv4 or IPv6 RLOC address, depending on whether the Map-Request is using an IPv4 or IPv6 header, respectively. In all cases, the UDP source port number for the Map-Request message is a 16-bit value selected by the ITR/PITR, and the UDP destination port number is set to the well- known destination port number 4342. A successful Map-Reply, which is one that has a nonce that matches an outstanding Map-Request nonce, will update the cached set of RLOCs associated with the EID-Prefix range.
One or more Map-Request ('ITR-RLOC-AFI', 'ITR-RLOC-Address') fields MUST be filled in by the ITR. The number of fields (minus 1) encoded MUST be placed in the 'IRC' field. The ITR MAY include all locally configured Locators in this list or just provide one locator address from each address family it supports. If the ITR erroneously provides no ITR-RLOC addresses, the Map-Replier MUST drop the Map-Request.
Map-Requests can also be LISP encapsulated using UDP destination port 4342 with a LISP Type value set to "Encapsulated Control Message", when sent from an ITR to a Map-Resolver. Likewise, Map-Requests are LISP encapsulated the same way from a Map-Server to an ETR. Details on Encapsulated Map-Requests and Map-Resolvers can be found in [RFC6833].
Map-Requests MUST be rate-limited. It is RECOMMENDED that a Map-Request for the same EID-Prefix be sent no more than once per second.
An ITR that is configured with mapping database information (i.e., it is also an ETR) MAY optionally include those mappings in a Map-Request. When an ETR configured to accept and verify such "piggybacked" mapping data receives such a Map-Request and it does
not have this mapping in the map-cache, it MAY originate a "verifying Map-Request", addressed to the map-requesting ITR and the ETR MAY add a Map-Cache entry. If the ETR has a Map-Cache entry that matches the "piggybacked" EID and the RLOC is in the Locator-Set for the entry, then it may send the "verifying Map-Request" directly to the originating Map-Request source. If the RLOC is not in the Locator-Set, then the ETR MUST send the "verifying Map-Request" to the "piggybacked" EID. Doing this forces the "verifying Map-Request" to go through the mapping database system to reach the authoritative source of information about that EID, guarding against RLOC-spoofing in the "piggybacked" mapping data.