286 строки
12 KiB
Plaintext
286 строки
12 KiB
Plaintext
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 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
|