ila: Add ila.txt

Identifier Locator Addressing (ILA)

Introduction

============

Identifier-locator addressing (ILA) is a technique used with IPv6 that

differentiates between location and identity of a network node. Part of an

address expresses the immutable identity of the node, and another part

indicates the location of the node which can be dynamic. Identifier-locator

addressing can be used to efficiently implement overlay networks for

network virtualization as well as solutions for use cases in mobility.

ILA can be thought of as means to implement an overlay network without

encapsulation. This is accomplished by performing network address

translation on destination addresses as a packet traverses a network. To

the network, an ILA translated packet appears to be no different than any

other IPv6 packet. For instance, if the transport protocol is TCP then an

ILA translated packet looks like just another TCP/IPv6 packet. The

advantage of this is that ILA is transparent to the network so that

optimizations in the network, such as ECMP, RSS, GRO, GSO, etc., just work.

The ILA protocol is described in Internet-Draft draft-herbert-intarea-ila.

ILA terminology

===============

  - Identifier	A number that identifies an addressable node in the network

		independent of its location. ILA identifiers are sixty-four

		bit values.

  - Locator	A network prefix that routes to a physical host. Locators

		provide the topological location of an addressed node. ILA

		locators are sixty-four bit prefixes.

  - ILA mapping

		A mapping of an ILA identifier to a locator (or to a

		locator and meta data). An ILA domain maintains a database

		that contains mappings for all destinations in the domain.

  - SIR address

		An IPv6 address composed of a SIR prefix (upper sixty-

		four bits) and an identifier (lower sixty-four bits).

		SIR addresses are visible to applications and provide a

		means for them to address nodes independent of their

		location.

  - ILA address

		An IPv6 address composed of a locator (upper sixty-four

		bits) and an identifier (low order sixty-four bits). ILA

		addresses are never visible to an application.

  - ILA host	An end host that is capable of performing ILA translations

		on transmit or receive.

  - ILA router	A network node that performs ILA translation and forwarding

		of translated packets.

  - ILA forwarding cache

		A type of ILA router that only maintains a working set

		cache of mappings.

  - ILA node	A network node capable of performing ILA translations. This

		can be an ILA router, ILA forwarding cache, or ILA host.

Operation

=========

There are two fundamental operations with ILA:

  - Translate a SIR address to an ILA address. This is performed on ingress

    to an ILA overlay.

  - Translate an ILA address to a SIR address. This is performed on egress

    from the ILA overlay.

ILA can be deployed either on end hosts or intermediate devices in the

network; these are provided by "ILA hosts" and "ILA routers" respectively.

Configuration and datapath for these two points of deployment is somewhat

different.

The diagram below illustrates the flow of packets through ILA as well

as showing ILA hosts and routers.

    +--------+                                                +--------+

    | Host A +-+                                         +--->| Host B |

    |        | |              (2) ILA                   (')   |        |

    +--------+ |            ...addressed....           (   )  +--------+

               V  +---+--+  .  packet      .  +---+--+  (_)

   (1) SIR     |  | ILA  |----->-------->---->| ILA  |   |   (3) SIR

    addressed  +->|router|  .              .  |router|->-+    addressed

    packet        +---+--+  .     IPv6     .  +---+--+        packet

                   /        .    Network   .

                  /         .              .   +--+-++--------+

    +--------+   /          .              .   |ILA ||  Host  |

    |  Host  +--+           .              .- -|host||        |

    |        |              .              .   +--+-++--------+

    +--------+              ................

Transport checksum handling

===========================

When an address is translated by ILA, an encapsulated transport checksum

that includes the translated address in a pseudo header may be rendered

incorrect on the wire. This is a problem for intermediate devices,

including checksum offload in NICs, that process the checksum. There are

three options to deal with this:

- no action	Allow the checksum to be incorrect on the wire. Before

		a receiver verifies a checksum the ILA to SIR address

		translation must be done.

- adjust transport checksum

		When ILA translation is performed the packet is parsed

		and if a transport layer checksum is found then it is

		adjusted to reflect the correct checksum per the

		translated address.

- checksum neutral mapping

		When an address is translated the difference can be offset

		elsewhere in a part of the packet that is covered by the

		the checksum. The low order sixteen bits of the identifier

		are used. This method is preferred since it doesn't require

		parsing a packet beyond the IP header and in most cases the

		adjustment can be precomputed and saved with the mapping.

Note that the checksum neutral adjustment affects the low order sixteen

bits of the identifier. When ILA to SIR address translation is done on

egress the low order bits are restored to the original value which

restores the identifier as it was originally sent.

Identifier types

================

ILA defines different types of identifiers for different use cases.

The defined types are:

      0: interface identifier

      1: locally unique identifier

      2: virtual networking identifier for IPv4 address

      3: virtual networking identifier for IPv6 unicast address

      4: virtual networking identifier for IPv6 multicast address

      5: non-local address identifier

In the current implementation of kernel ILA only locally unique identifiers

(LUID) are supported. LUID allows for a generic, unformatted 64 bit

identifier.

Identifier formats

==================

Kernel ILA supports two optional fields in an identifier for formatting:

"C-bit" and "identifier type". The presence of these fields is determined

by configuration as demonstrated below.

If the identifier type is present it occupies the three highest order

bits of an identifier. The possible values are given in the above list.

If the C-bit is present,  this is used as an indication that checksum

neutral mapping has been done. The C-bit can only be set in an

ILA address, never a SIR address.

In the simplest format the identifier types, C-bit, and checksum

adjustment value are not present so an identifier is considered an

unstructured sixty-four bit value.

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |                            Identifier                         |

     +                                                               +

     |                                                               |

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The checksum neutral adjustment may be configured to always be

present using neutral-map-auto. In this case there is no C-bit, but the

checksum adjustment is in the low order 16 bits. The identifier is

still sixty-four bits.

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |                            Identifier                         |

     |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |                               |  Checksum-neutral adjustment  |

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The C-bit may used to explicitly indicate that checksum neutral

mapping has been applied to an ILA address. The format is:

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |     |C|                    Identifier                         |

     |     +-+                       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |                               |  Checksum-neutral adjustment  |

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The identifier type field may be present to indicate the identifier

type. If it is not present then the type is inferred based on mapping

configuration. The checksum neutral adjustment may automatically

used with the identifier type as illustrated below.

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     | Type|                      Identifier                         |

     +-+-+-+                         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |                               |  Checksum-neutral adjustment  |

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

If the identifier type and the C-bit can be present simultaneously so

the identifier format would be:

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     | Type|C|                    Identifier                         |

     +-+-+-+-+                       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |                               |  Checksum-neutral adjustment  |

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Configuration

=============

There are two methods to configure ILA mappings. One is by using LWT routes

and the other is ila_xlat (called from NFHOOK PREROUTING hook). ila_xlat

is intended to be used in the receive path for ILA hosts .

An ILA router has also been implemented in XDP. Description of that is

outside the scope of this document.

The usage of for ILA LWT routes is:

ip route add DEST/128 encap ila LOC csum-mode MODE ident-type TYPE via ADDR

Destination (DEST) can either be a SIR address (for an ILA host or ingress

ILA router) or an ILA address (egress ILA router). LOC is the sixty-four

bit locator (with format W:X:Y:Z) that overwrites the upper sixty-four

bits of the destination address.  Checksum MODE is one of "no-action",

"adj-transport", "neutral-map", and "neutral-map-auto". If neutral-map is

set then the C-bit will be present. Identifier TYPE one of "luid" or

"use-format." In the case of use-format, the identifier type field is

present and the effective type is taken from that.

The usage of ila_xlat is:

ip ila add loc_match MATCH loc LOC csum-mode MODE ident-type TYPE

MATCH indicates the incoming locator that must be matched to apply

a the translaiton. LOC is the locator that overwrites the upper

sixty-four bits of the destination address. MODE and TYPE have the

same meanings as described above.

Some examples

=============

# Configure an ILA route that uses checksum neutral mapping as well

# as type field. Note that the type field is set in the SIR address

# (the 2000 implies type is 1 which is LUID).

ip route add 3333:0:0:1:2000:0:1:87/128 encap ila 2001:0:87:0 \

     csum-mode neutral-map ident-type use-format

# Configure an ILA LWT route that uses auto checksum neutral mapping

# (no C-bit) and configure identifier type to be LUID so that the

# identifier type field will not be present.

ip route add 3333:0:0:1:2000:0:2:87/128 encap ila 2001:0:87:1 \

     csum-mode neutral-map-auto ident-type luid

ila_xlat configuration

# Configure an ILA to SIR mapping that matches a locator and overwrites

# it with a SIR address (3333:0:0:1 in this example). The C-bit and

# identifier field are used.

ip ila add loc_match 2001:0:119:0 loc 3333:0:0:1 \

    csum-mode neutral-map-auto ident-type use-format

# Configure an ILA to SIR mapping where checksum neutral is automatically

# set without the C-bit and the identifier type is configured to be LUID

# so that the identifier type field is not present.

ip ila add loc_match 2001:0:119:0 loc 3333:0:0:1 \

    csum-mode neutral-map-auto ident-type use-format