10.3. Fast Endpoint Mobility
10.3. Fast Endpoint Mobility
Fast endpoint mobility occurs when an endpoint moves relatively rapidly, changing its IP-layer network attachment point. Maintenance of session continuity is a goal. This is where the Mobile IPv4 [RFC5944] and Mobile IPv6 [RFC6275] [RFC4866] mechanisms are used and primarily where interactions with LISP need to be explored.
The problem is that as an endpoint moves, it may require changes to the mapping between its EID and a set of RLOCs for its new network location. When this is added to the overhead of Mobile IP binding updates, some packets might be delayed or dropped.
In IPv4 mobility, when an endpoint is away from home, packets to it are encapsulated and forwarded via a home agent that resides in the home area the endpoint's address belongs to. The home agent will encapsulate and forward packets either directly to the endpoint or to a foreign agent that resides where the endpoint has moved to. Packets from the endpoint may be sent directly to the correspondent node, may be sent via the foreign agent, or may be reverse-tunneled back to the home agent for delivery to the mobile node. As the mobile node's EID or available RLOC changes, LISP EID-to-RLOC
mappings are required for communication between the mobile node and the home agent, whether via the foreign agent or not. As a mobile endpoint changes networks, up to three LISP mapping changes may be required:
o The mobile node moves from an old location to a new visited network location and notifies its home agent that it has done so. The Mobile IPv4 control packets the mobile node sends pass through one of the new visited network's ITRs, which needs an EID-to-RLOC mapping for the home agent.
o The home agent might not have the EID-to-RLOC mappings for the mobile node's "care-of" address or its foreign agent in the new visited network, in which case it will need to acquire them.
o When packets are sent directly to the correspondent node, it may be that no traffic has been sent from the new visited network to the correspondent node's network, and the new visited network's ITR will need to obtain an EID-to-RLOC mapping for the correspondent node's site.
In addition, if the IPv4 endpoint is sending packets from the new visited network using its original EID, then LISP will need to perform a route-returnability check on the new EID-to-RLOC mapping for that EID.
In IPv6 mobility, packets can flow directly between the mobile node and the correspondent node in either direction. The mobile node uses its "care-of" address (EID). In this case, the route-returnability check would not be needed but one more LISP mapping lookup may be required instead:
o As above, three mapping changes may be needed for the mobile node to communicate with its home agent and to send packets to the correspondent node.
o In addition, another mapping will be needed in the correspondent node's ITR, in order for the correspondent node to send packets to the mobile node's "care-of" address (EID) at the new network location.
When both endpoints are mobile, the number of potential mapping lookups increases accordingly.
As a mobile node moves, there are not only mobility state changes in the mobile node, correspondent node, and home agent, but also state changes in the ITRs and ETRs for at least some EID-Prefixes.
The goal is to support rapid adaptation, with little delay or packet loss for the entire system. Also, IP mobility can be modified to require fewer mapping changes. In order to increase overall system performance, there may be a need to reduce the optimization of one area in order to place fewer demands on another.
In LISP, one possibility is to "glean" information. When a packet arrives, the ETR could examine the EID-to-RLOC mapping and use that mapping for all outgoing traffic to that EID. It can do this after performing a route-returnability check, to ensure that the new network location does have an internal route to that endpoint. However, this does not cover the case where an ITR (the node assigned the RLOC) at the mobile-node location has been compromised.
Mobile IP packet exchange is designed for an environment in which all routing information is disseminated before packets can be forwarded. In order to allow the Internet to grow to support expected future use, we are moving to an environment where some information may have to be obtained after packets are in flight. Modifications to IP mobility should be considered in order to optimize the behavior of the overall system. Anything that decreases the number of new EID-to-RLOC mappings needed when a node moves, or maintains the validity of an EID-to-RLOC mapping for a longer time, is useful.