6.6.3. Database Map-Versioning

6.6.3. Database Map-Versioning

When there is unidirectional packet flow between an ITR and ETR, and the EID-to-RLOC mappings change on the ETR, it needs to inform the ITR so encapsulation to a removed Locator can stop and can instead be started to a new Locator in the Locator-Set.

An ETR, when it sends Map-Reply messages, conveys its own Map-Version Number. This is known as the Destination Map-Version Number. ITRs include the Destination Map-Version Number in packets they encapsulate to the site. When an ETR decapsulates a packet and detects that the Destination Map-Version Number is less than the current version for its mapping, the SMR procedure described in Section 6.6.2 occurs.

An ITR, when it encapsulates packets to ETRs, can convey its own Map-Version Number. This is known as the Source Map-Version Number. When an ETR decapsulates a packet and detects that the Source Map-Version Number is greater than the last Map-Version Number sent in a Map-Reply from the ITR's site, the ETR will send a Map-Request to one of the ETRs for the source site.

A Map-Version Number is used as a sequence number per EID-Prefix, so values that are greater are considered to be more recent. A value of 0 for the Source Map-Version Number or the Destination Map-Version Number conveys no versioning information, and an ITR does no comparison with previously received Map-Version Numbers.

A Map-Version Number can be included in Map-Register messages as well. This is a good way for the Map-Server to assure that all ETRs for a site registering to it will be synchronized according to Map-Version Number.

See [RFC6834] for a more detailed analysis and description of Database Map-Versioning.