3. Definition of Terms
3. Definition of Terms
Provider-Independent (PI) Addresses: PI addresses are an address block assigned from a pool where blocks are not associated with any particular location in the network (e.g., from a particular service provider) and are therefore not topologically aggregatable in the routing system.
Provider-Assigned (PA) Addresses: PA addresses are an address block assigned to a site by each service provider to which a site connects. Typically, each block is a sub-block of a service provider Classless Inter-Domain Routing (CIDR) [RFC4632] block and is aggregated into the larger block before being advertised into the global Internet. Traditionally, IP multihoming has been implemented by each multihomed site acquiring its own globally visible prefix. LISP uses only topologically assigned and aggregatable address blocks for RLOCs, eliminating this demonstrably non-scalable practice.
Routing Locator (RLOC): An RLOC is an IPv4 [RFC0791] or IPv6 [RFC2460] address of an Egress Tunnel Router (ETR). An RLOC is the output of an EID-to-RLOC mapping lookup. An EID maps to one or more RLOCs. Typically, RLOCs are numbered from topologically aggregatable blocks that are assigned to a site at each point to which it attaches to the global Internet; where the topology is defined by the connectivity of provider networks, RLOCs can be thought of as PA addresses. Multiple RLOCs can be assigned to the same ETR device or to multiple ETR devices at a site.
Endpoint ID (EID): An EID is a 32-bit (for IPv4) or 128-bit (for IPv6) value used in the source and destination address fields of the first (most inner) LISP header of a packet. The host obtains a destination EID the same way it obtains a destination address today, for example, through a Domain Name System (DNS) [RFC1034] lookup or Session Initiation Protocol (SIP) [RFC3261] exchange. The source EID is obtained via existing mechanisms used to set a host's "local" IP address. An EID used on the public Internet must have the same properties as any other IP address used in that manner; this means, among other things, that it must be globally unique. An EID is allocated to a host from an EID-Prefix block associated with the site where the host is located. An EID can be used by a host to refer to other hosts. EIDs MUST NOT be used as LISP RLOCs. Note that EID blocks MAY be assigned in a hierarchical manner, independent of the network topology, to facilitate scaling of the mapping database. In addition, an EID block assigned to a site may have site-local structure (subnetting) for routing within the site; this structure is not visible to the global routing system.
EID-Prefix: An EID-Prefix is a power-of-two block of EIDs that are allocated to a site by an address allocation authority. EID-Prefixes are associated with a set of RLOC addresses that make up a "database mapping". EID-Prefix allocations can be broken up into smaller blocks when an RLOC set is to be associated with the larger EID-Prefix block.
End-System: An end-system is an IPv4 or IPv6 device that originates packets with a single IPv4 or IPv6 header. The end-system supplies an EID value for the destination address field of the IP header when communicating globally (i.e., outside of its routing domain). An end-system can be a host computer, a switch or router device, or any network appliance.
Ingress Tunnel Router (ITR): An ITR is a router that accepts an IP packet with a single IP header (more specifically, an IP packet that does not contain a LISP header). The router treats this "inner" IP destination address as an EID and performs an EID-to-RLOC mapping lookup. The router then prepends an "outer" IP header with one of its globally routable RLOCs in the source address field and the result of the mapping lookup in the destination address field. Note that this destination RLOC may be an intermediate, proxy device that has better knowledge of the EID-to-RLOC mapping closer to the destination EID. In general, an ITR receives IP packets from site end-systems on one side and sends LISP-encapsulated IP packets toward the Internet on the other side.
TE ITR: A TE ITR is an ITR that is deployed in a LISP site when the site is used as a transit network between non-LISP sites. Transit network policy and traffic engineering may be applied to the packets that are tunneled through the site when the EID destinations are addresses outside of the LISP site and LISP TE ITRs are used.
Egress Tunnel Router (ETR): An ETR is a router that accepts an IP packet where the destination address in the "outer" IP header is one of its own RLOCs. The router strips the "outer" header and forwards the packet based on the next IP header found. In general, an ETR receives LISP-encapsulated IP packets from the Internet on one side and sends decapsulated IP packets to site end-systems on the other side. ETR functionality does not have to be limited to a router device. A server host can be the endpoint of a LISP tunnel as well.
TE ETR: A TE ETR is an ETR that is deployed in a LISP site when the site is used as a transit network between non-LISP sites. TE ETRs are the devices that terminate tunnels initiated by TE ITRs. See the definition of a TE ITR for further details.
xTR: An xTR is a reference to an ITR or ETR when direction of data flow is not part of the context description. xTR refers to the router that is the tunnel endpoint and is used synonymously with the term "Tunnel Router". For example, "an xTR can be located at the Customer Edge (CE) router" indicates both ITR and ETR functionality at the CE router.
LISP Header: LISP header is a term used to refer to the outer IPv4 or IPv6 header, a UDP header, and a LISP-specific 8-octet header that follow the UDP header and that an ITR prepends or an ETR strips.
Address Family Identifier (AFI): AFI is a term used to describe an address encoding in a packet. An address family that pertains to LISP is an AFI listed in [AFI]. An AFI value of 0 used in this specification indicates an unspecified encoded address where the length of the address is 0 octets following the 16-bit AFI value of 0.
Negative Mapping Entry: A negative mapping entry, also known as a negative cache entry, is an EID-to-RLOC entry where an EID-Prefix is advertised or stored with no RLOCs. That is, the locator-set for the EID-Prefix is empty or has an encoded locator-count of 0. This type of entry could be used to describe a prefix from a non-LISP site, which is not reachable through the mapping system.
Data Probe: A data probe is a LISP-encapsulated data packet where the inner-header destination address equals the outer-header destination address used to trigger a Map-Reply by a decapsulating ETR. In addition, the original packet is decapsulated and delivered to the destination host if the destination EID matches the EID-Prefix of a configured EID-to-RLOC database mapping. Otherwise, the packet is dropped. A Data Probe is used in the destination RLOC reachability algorithms described in Section 6.3.2.
Routing Locator Reachability: Routing Locator reachability is an algorithm used to determine reachability of RLOCs in an RLOC-set. See Section 6.3 for details.
Gleaning: Gleaning is the term used to describe a process where an ETR learns the mapping information of another ETR. When an ITR encapsulates a packet to an ETR, the ETR can glean the RLOC address from the outer header as well as the EID from the inner header and use that address pair as the mapping information for an EID-to-RLOC cache entry. An ETR MUST NOT use gleaned mapping information for subsequent destinations until the legitimacy of the mapping is verified by a Map-Request/Map-Reply exchange.