BNG subscriber
This is a broader term than the ESM Subscriber, independent of the platform on which the subscriber is instantiated. It includes ESM subscribers on 7750 SR as well as subscribers instantiated on third party BNGs. Some of the NAT functions, such as Subscriber Aware Large Scale NAT44 utilizing standard RADIUS attribute work with subscribers independently of the platform on which they are instantiated.
deterministic NAT
This is a mode of operation where mappings between the NAT subscriber and the outside IP address and port-range are allocated at the time of configuration. Each subscriber is permanently mapped to an outside IP and a dedicated port block. This dedicated port block is referred to as deterministic port block. Logging is not needed as the reverse mapping can be obtained using a known formula. The subscriber’s ports can be expanded by allocating a dynamic port block in case that all ports in deterministic port block are exhausted. In such case logging for the dynamic port block allocation/de-allocation is required.
Enhanced Subscriber Management (ESM) subscriber
This is a host or a collection of hosts instantiated in 7750 SR Broadband Network Gateway (BNG). The ESM subscriber represents a household or a business entity for which various services with committed Service Level Agreements (SLA) can be delivered. NAT function is not part of basic ESM functionality.
L2-Aware NAT
In the context of 7750 SR platform combines Enhanced Subscriber Management (ESM) subscriber-id and inside IP address to perform translation into a unique outside IP address and outside port. This is in contrast with classical NAT technique where only inside IP is considered for address translations. Because the subscriber-id alone is sufficient to make the address translation unique, L2-Aware NAT allows many ESM subscribers to share the same inside IP address. The scalability, performance and reliability requirements are the same as in LSN.
Large Scale NAT (LSN)
This refers to a collection of network address translation techniques used in service provider network implemented on a highly scalable, high performance hardware that facilitates various intra and inter-node redundancy mechanisms. The purpose of LSN semantics is to make delineation between high scale and high performance NAT functions found in service provider networks and enterprise NAT that is usually serving much smaller customer base at smaller speeds. The following NAT techniques can be grouped under the LSN name:
Large Scale NAT44 or Carrier Grade NAT (CGN)
DS-Lite
NAT64
Each distinct NAT technique is referred to by its corresponding name (Large Scale NAT44 [or CGN], DS-Lite and NAT64) with the understanding that in the context of 7750 SR platform, they are all part of LSN (and not enterprise based NAT).
Large Scale NAT44 term can be interchangeably used with the term Carrier Grade NAT (CGN) which in its name implies high reliability, high scale and high performance. These are again typical requirements found in service provider (carrier) network.
NAT RADIUS accounting
This is the reporting (or logging) of address translation related events (port-block allocation/de-allocation) via RADIUS accounting facility. NAT RADIUS accounting is facilitated via regular RADIUS accounting messages (start/interim-update/stop) as defined in RFC 2866, RADIUS Accounting, with NAT specific VSAs.
NAT RADIUS accounting
This can be used interchangeably with the term NAT RADIUS logging.
NAT subscriber
In NAT terminology, a NAT subscriber is an inside entity whose true identity is hidden from the outside. There are a few types of NAT implementation in 7750 SR and subscribers for each implementation are defined as follows:
Large Scale NAT44 (or CGN)
The subscriber is an inside IPv4 address.
L2-Aware NAT
The subscriber is an ESM subscriber which can spawn multiple IPv4 inside addresses.
DS-Lite
The subscriber in DS-Lite can be identified by the CPE’s IPv6 address (B4 element) or an IPv6 prefix. The selection of address or prefix as the representation of a DS-Lite subscriber is configuration dependent.
NAT64
The subscriber is an IPv6 prefix.
non-deterministic NAT
This is a mode of operation where all outside IP address and port block allocations are made dynamically at the time of subscriber instantiation. Logging in such case is required.
port block
This is collection of ports that is assigned to a subscriber. A deterministic LSN subscriber can have only one deterministic port block that can be extended by multiple dynamic port blocks. Non-deterministic LSN subscriber can be assigned only dynamic port blocks. All port blocks for a LSN subscriber must be allocated from a single outside IP address.
port-range
This is a collection of ports that can spawn multiple port blocks of the same type. For example, deterministic port-range includes all ports that are reserved for deterministic consumption. Similarly dynamic port-range is a total collection of ports that can be allocated in the form of dynamic port blocks. Other types of port-ranges are well-known ports and static port forwards.