RFC 7296
Internet Key Exchange Protocol Version 2 (IKEv2)
Pages: 142
Internet Standard: 79
→ Errata
Obsoletes: 5996
Updated by: 7427 7670 8247 8983 9370
Internet Standard: 79
→ Errata
Obsoletes: 5996
Updated by: 7427 7670 8247 8983 9370
Part 5 of 6 – Pages 99 to 124
3.10. Notify Payload
The Notify payload, denoted N in this document, is used to transmit informational data, such as error conditions and state transitions, to an IKE peer. A Notify payload may appear in a response message (usually specifying why a request was rejected), in an INFORMATIONAL exchange (to report an error not in an IKE request), or in any other message to indicate sender capabilities or to modify the meaning of the request.
The Notify payload is defined as follows: 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Payload |C| RESERVED | Payload Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Protocol ID | SPI Size | Notify Message Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Security Parameter Index (SPI) ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Notification Data ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 16: Notify Payload Format o Protocol ID (1 octet) - If this notification concerns an existing SA whose SPI is given in the SPI field, this field indicates the type of that SA. For notifications concerning Child SAs, this field MUST contain either (2) to indicate AH or (3) to indicate ESP. Of the notifications defined in this document, the SPI is included only with INVALID_SELECTORS, REKEY_SA, and CHILD_SA_NOT_FOUND. If the SPI field is empty, this field MUST be sent as zero and MUST be ignored on receipt. o SPI Size (1 octet) - Length in octets of the SPI as defined by the IPsec protocol ID or zero if no SPI is applicable. For a notification concerning the IKE SA, the SPI Size MUST be zero and the field must be empty. o Notify Message Type (2 octets) - Specifies the type of notification message. o SPI (variable length) - Security Parameter Index. o Notification Data (variable length) - Status or error data transmitted in addition to the Notify Message Type. Values for this field are type specific (see below). The payload type for the Notify payload is forty-one (41).
3.10.1. Notify Message Types
Notification information can be error messages specifying why an SA could not be established. It can also be status data that a process managing an SA database wishes to communicate with a peer process. The table below lists the notification messages and their corresponding values. The number of different error statuses was greatly reduced from IKEv1 both for simplification and to avoid giving configuration information to probers. Types in the range 0 - 16383 are intended for reporting errors. An implementation receiving a Notify payload with one of these types that it does not recognize in a response MUST assume that the corresponding request has failed entirely. Unrecognized error types in a request and status types in a request or response MUST be ignored, and they should be logged. Notify payloads with status types MAY be added to any message and MUST be ignored if not recognized. They are intended to indicate capabilities, and as part of SA negotiation, are used to negotiate non-cryptographic parameters. More information on error handling can be found in Section 2.21. The values in the following table are only current as of the publication date of RFC 4306, plus two error types added in this document. Other values may have been added since then or will be added after the publication of this document. Readers should refer to [IKEV2IANA] for the latest values. NOTIFY messages: error types Value ------------------------------------------------------------------- UNSUPPORTED_CRITICAL_PAYLOAD 1 See Section 2.5. INVALID_IKE_SPI 4 See Section 2.21. INVALID_MAJOR_VERSION 5 See Section 2.5. INVALID_SYNTAX 7 Indicates the IKE message that was received was invalid because some type, length, or value was out of range or because the request was rejected for policy reasons. To avoid a DoS attack using forged messages, this status may only be returned for and in an encrypted packet if the Message ID and
cryptographic checksum were valid. To avoid leaking information
to someone probing a node, this status MUST be sent in response
to any error not covered by one of the other status types.
To aid debugging, more detailed error information should be
written to a console or log.
INVALID_MESSAGE_ID 9
See Section 2.3.
INVALID_SPI 11
See Section 1.5.
NO_PROPOSAL_CHOSEN 14
None of the proposed crypto suites was acceptable. This can be
sent in any case where the offered proposals (including but not
limited to SA payload values, USE_TRANSPORT_MODE notify,
IPCOMP_SUPPORTED notify) are not acceptable for the responder.
This can also be used as "generic" Child SA error when Child SA
cannot be created for some other reason. See also Section 2.7.
INVALID_KE_PAYLOAD 17
See Sections 1.2 and 1.3.
AUTHENTICATION_FAILED 24
Sent in the response to an IKE_AUTH message when, for some
reason, the authentication failed. There is no associated
data. See also Section 2.21.2.
SINGLE_PAIR_REQUIRED 34
See Section 2.9.
NO_ADDITIONAL_SAS 35
See Section 1.3.
INTERNAL_ADDRESS_FAILURE 36
See Section 3.15.4.
FAILED_CP_REQUIRED 37
See Section 2.19.
TS_UNACCEPTABLE 38
See Section 2.9.
INVALID_SELECTORS 39
MAY be sent in an IKE INFORMATIONAL exchange when a node receives
an ESP or AH packet whose selectors do not match those of the SA
on which it was delivered (and that caused the packet to be
dropped). The Notification Data contains the start of the
offending packet (as in ICMP messages) and the SPI field of the
notification is set to match the SPI of the Child SA.
TEMPORARY_FAILURE 43
See Section 2.25.
CHILD_SA_NOT_FOUND 44
See Section 2.25.
NOTIFY messages: status types Value
-------------------------------------------------------------------
INITIAL_CONTACT 16384
See Section 2.4.
SET_WINDOW_SIZE 16385
See Section 2.3.
ADDITIONAL_TS_POSSIBLE 16386
See Section 2.9.
IPCOMP_SUPPORTED 16387
See Section 2.22.
NAT_DETECTION_SOURCE_IP 16388
See Section 2.23.
NAT_DETECTION_DESTINATION_IP 16389
See Section 2.23.
COOKIE 16390
See Section 2.6.
USE_TRANSPORT_MODE 16391
See Section 1.3.1.
HTTP_CERT_LOOKUP_SUPPORTED 16392
See Section 3.6.
REKEY_SA 16393
See Section 1.3.3.
ESP_TFC_PADDING_NOT_SUPPORTED 16394
See Section 1.3.1.
NON_FIRST_FRAGMENTS_ALSO 16395
See Section 1.3.1.
3.11. Delete Payload
The Delete payload, denoted D in this document, contains a
protocol-specific Security Association identifier that the sender has
removed from its Security Association database and is, therefore, no
longer valid. Figure 17 shows the format of the Delete payload. It
is possible to send multiple SPIs in a Delete payload; however, each
SPI MUST be for the same protocol. Mixing of protocol identifiers
MUST NOT be performed in the Delete payload. It is permitted,
however, to include multiple Delete payloads in a single
INFORMATIONAL exchange where each Delete payload lists SPIs for a
different protocol.
Deletion of the IKE SA is indicated by a protocol ID of 1 (IKE) but
no SPIs. Deletion of a Child SA, such as ESP or AH, will contain the
IPsec protocol ID of that protocol (2 for AH, 3 for ESP), and the SPI
is the SPI the sending endpoint would expect in inbound ESP or AH
packets.
The Delete payload is defined as follows:
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Payload |C| RESERVED | Payload Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol ID | SPI Size | Num of SPIs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Security Parameter Index(es) (SPI) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 17: Delete Payload Format
o Protocol ID (1 octet) - Must be 1 for an IKE SA, 2 for AH, or 3
for ESP.
o SPI Size (1 octet) - Length in octets of the SPI as defined by the
protocol ID. It MUST be zero for IKE (SPI is in message header)
or four for AH and ESP.
o Num of SPIs (2 octets, unsigned integer) - The number of SPIs
contained in the Delete payload. The size of each SPI is defined
by the SPI Size field.
o Security Parameter Index(es) (variable length) - Identifies the
specific Security Association(s) to delete. The length of this
field is determined by the SPI Size and Num of SPIs fields.
The payload type for the Delete payload is forty-two (42).
3.12. Vendor ID Payload
The Vendor ID payload, denoted V in this document, contains a vendor-
defined constant. The constant is used by vendors to identify and
recognize remote instances of their implementations. This mechanism
allows a vendor to experiment with new features while maintaining
backward compatibility.
A Vendor ID payload MAY announce that the sender is capable of
accepting certain extensions to the protocol, or it MAY simply
identify the implementation as an aid in debugging. A Vendor ID
payload MUST NOT change the interpretation of any information defined
in this specification (i.e., the critical bit MUST be set to 0).
Multiple Vendor ID payloads MAY be sent. An implementation is not
required to send any Vendor ID payload at all.
A Vendor ID payload may be sent as part of any message. Reception of
a familiar Vendor ID payload allows an implementation to make use of
private use numbers described throughout this document, such as
private payloads, private exchanges, private notifications, etc.
Unfamiliar Vendor IDs MUST be ignored.
Writers of documents who wish to extend this protocol MUST define a
Vendor ID payload to announce the ability to implement the extension
in the document. It is expected that documents that gain acceptance
and are standardized will be given "magic numbers" out of the Future
Use range by IANA, and the requirement to use a Vendor ID will go
away.
The Vendor ID payload fields are defined as follows: 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Payload |C| RESERVED | Payload Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Vendor ID (VID) ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 18: Vendor ID Payload Format o Vendor ID (variable length) - It is the responsibility of the person choosing the Vendor ID to assure its uniqueness in spite of the absence of any central registry for IDs. Good practice is to include a company name, a person name, or some such information. If you want to show off, you might include the latitude and longitude and time where you were when you chose the ID and some random input. A message digest of a long unique string is preferable to the long unique string itself. The payload type for the Vendor ID payload is forty-three (43).3.13. Traffic Selector Payload
The Traffic Selector payload, denoted TS in this document, allows peers to identify packet flows for processing by IPsec security services. The Traffic Selector payload consists of the IKE generic payload header followed by individual Traffic Selectors as follows: 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Payload |C| RESERVED | Payload Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Number of TSs | RESERVED | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ <Traffic Selectors> ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 19: Traffic Selectors Payload Format o Number of TSs (1 octet) - Number of Traffic Selectors being provided.
o RESERVED - This field MUST be sent as zero and MUST be ignored on
receipt.
o Traffic Selectors (variable length) - One or more individual
Traffic Selectors.
The length of the Traffic Selector payload includes the TS header and
all the Traffic Selectors.
The payload type for the Traffic Selector payload is forty-four (44)
for addresses at the initiator's end of the SA and forty-five (45)
for addresses at the responder's end.
There is no requirement that TSi and TSr contain the same number of
individual Traffic Selectors. Thus, they are interpreted as follows:
a packet matches a given TSi/TSr if it matches at least one of the
individual selectors in TSi, and at least one of the individual
selectors in TSr.
For instance, the following Traffic Selectors:
TSi = ((17, 100, 198.51.100.66-198.51.100.66),
(17, 200, 198.51.100.66-198.51.100.66))
TSr = ((17, 300, 0.0.0.0-255.255.255.255),
(17, 400, 0.0.0.0-255.255.255.255))
would match UDP packets from 198.51.100.66 to anywhere, with any of
the four combinations of source/destination ports (100,300),
(100,400), (200,300), and (200, 400).
Thus, some types of policies may require several Child SA pairs. For
instance, a policy matching only source/destination ports (100,300)
and (200,400), but not the other two combinations, cannot be
negotiated as a single Child SA pair.
3.13.1. Traffic Selector
1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TS Type |IP Protocol ID*| Selector Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Start Port* | End Port* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Starting Address* ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Ending Address* ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 20: Traffic Selector *Note: All fields other than TS Type and Selector Length depend on the TS Type. The fields shown are for TS Types 7 and 8, the only two values currently defined. o TS Type (one octet) - Specifies the type of Traffic Selector. o IP protocol ID (1 octet) - Value specifying an associated IP protocol ID (such as UDP, TCP, and ICMP). A value of zero means that the protocol ID is not relevant to this Traffic Selector -- the SA can carry all protocols. o Selector Length (2 octets, unsigned integer) - Specifies the length of this Traffic Selector substructure including the header. o Start Port (2 octets, unsigned integer) - Value specifying the smallest port number allowed by this Traffic Selector. For protocols for which port is undefined (including protocol 0), or if all ports are allowed, this field MUST be zero. ICMP and ICMPv6 Type and Code values, as well as Mobile IP version 6 (MIPv6) mobility header (MH) Type values, are represented in this field as specified in Section 4.4.1.1 of [IPSECARCH]. ICMP Type and Code values are treated as a single 16-bit integer port number, with Type in the most significant eight bits and Code in the least significant eight bits. MIPv6 MH Type values are treated as a single 16-bit integer port number, with Type in the most significant eight bits and the least significant eight bits set to zero.
o End Port (2 octets, unsigned integer) - Value specifying the
largest port number allowed by this Traffic Selector. For
protocols for which port is undefined (including protocol 0), or
if all ports are allowed, this field MUST be 65535. ICMP and
ICMPv6 Type and Code values, as well as MIPv6 MH Type values, are
represented in this field as specified in Section 4.4.1.1 of
[IPSECARCH]. ICMP Type and Code values are treated as a single
16-bit integer port number, with Type in the most significant
eight bits and Code in the least significant eight bits. MIPv6 MH
Type values are treated as a single 16-bit integer port number,
with Type in the most significant eight bits and the least
significant eight bits set to zero.
o Starting Address - The smallest address included in this Traffic
Selector (length determined by TS Type).
o Ending Address - The largest address included in this Traffic
Selector (length determined by TS Type).
Systems that are complying with [IPSECARCH] that wish to indicate
"ANY" ports MUST set the start port to 0 and the end port to 65535;
note that according to [IPSECARCH], "ANY" includes "OPAQUE". Systems
working with [IPSECARCH] that wish to indicate "OPAQUE" ports, but
not "ANY" ports, MUST set the start port to 65535 and the end port
to 0.
The Traffic Selector types 7 and 8 can also refer to ICMP or ICMPv6
type and code fields, as well as MH Type fields for the IPv6 mobility
header [MIPV6]. Note, however, that neither ICMP nor MIPv6 packets
have separate source and destination fields. The method for
specifying the Traffic Selectors for ICMP and MIPv6 is shown by
example in Section 4.4.1.3 of [IPSECARCH].
The following table lists values for the Traffic Selector Type field and the corresponding Address Selector Data. The values in the following table are only current as of the publication date of RFC 4306. Other values may have been added since then or will be added after the publication of this document. Readers should refer to [IKEV2IANA] for the latest values. TS Type Value ------------------------------------------------------------------- TS_IPV4_ADDR_RANGE 7 A range of IPv4 addresses, represented by two four-octet values. The first value is the beginning IPv4 address (inclusive) and the second value is the ending IPv4 address (inclusive). All addresses falling between the two specified addresses are considered to be within the list. TS_IPV6_ADDR_RANGE 8 A range of IPv6 addresses, represented by two sixteen-octet values. The first value is the beginning IPv6 address (inclusive) and the second value is the ending IPv6 address (inclusive). All addresses falling between the two specified addresses are considered to be within the list.3.14. Encrypted Payload
The Encrypted payload, denoted SK {...} in this document, contains other payloads in encrypted form. The Encrypted payload, if present in a message, MUST be the last payload in the message. Often, it is the only payload in the message. This payload is also called the "Encrypted and Authenticated" payload. The algorithms for encryption and integrity protection are negotiated during IKE SA setup, and the keys are computed as specified in Sections 2.14 and 2.18. This document specifies the cryptographic processing of Encrypted payloads using a block cipher in CBC mode and an integrity check algorithm that computes a fixed-length checksum over a variable size message. The design is modeled after the ESP algorithms described in RFCs 2104 [HMAC], 4303 [ESP], and 2451 [ESPCBC]. This document completely specifies the cryptographic processing of IKE data, but those documents should be consulted for design rationale. Future documents may specify the processing of Encrypted payloads for other types of transforms, such as counter mode encryption and authenticated encryption algorithms. Peers MUST NOT negotiate transforms for which no such specification exists.
When an authenticated encryption algorithm is used to protect the IKE SA, the construction of the Encrypted payload is different than what is described here. See [AEAD] for more information on authenticated encryption algorithms and their use in IKEv2. The payload type for an Encrypted payload is forty-six (46). The Encrypted payload consists of the IKE generic payload header followed by individual fields as follows: 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Payload |C| RESERVED | Payload Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Initialization Vector | | (length is block size for encryption algorithm) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Encrypted IKE Payloads ~ + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | Padding (0-255 octets) | +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+ | | Pad Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Integrity Checksum Data ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 21: Encrypted Payload Format o Next Payload - The payload type of the first embedded payload. Note that this is an exception in the standard header format, since the Encrypted payload is the last payload in the message and therefore the Next Payload field would normally be zero. But because the content of this payload is embedded payloads and there was no natural place to put the type of the first one, that type is placed here. o Payload Length - Includes the lengths of the header, initialization vector (IV), Encrypted IKE payloads, Padding, Pad Length, and Integrity Checksum Data. o Initialization Vector - For CBC mode ciphers, the length of the initialization vector (IV) is equal to the block length of the underlying encryption algorithm. Senders MUST select a new unpredictable IV for every message; recipients MUST accept any value. The reader is encouraged to consult [MODES] for advice on IV generation. In particular, using the final ciphertext block of
the previous message is not considered unpredictable. For modes
other than CBC, the IV format and processing is specified in the
document specifying the encryption algorithm and mode.
o IKE payloads are as specified earlier in this section. This field
is encrypted with the negotiated cipher.
o Padding MAY contain any value chosen by the sender, and MUST have
a length that makes the combination of the payloads, the Padding,
and the Pad Length to be a multiple of the encryption block size.
This field is encrypted with the negotiated cipher.
o Pad Length is the length of the Padding field. The sender SHOULD
set the Pad Length to the minimum value that makes the combination
of the payloads, the Padding, and the Pad Length a multiple of the
block size, but the recipient MUST accept any length that results
in proper alignment. This field is encrypted with the negotiated
cipher.
o Integrity Checksum Data is the cryptographic checksum of the
entire message starting with the Fixed IKE header through the Pad
Length. The checksum MUST be computed over the encrypted message.
Its length is determined by the integrity algorithm negotiated.
3.15. Configuration Payload
The Configuration payload, denoted CP in this document, is used to
exchange configuration information between IKE peers. The exchange
is for an IRAC to request an internal IP address from an IRAS and to
exchange other information of the sort that one would acquire with
Dynamic Host Configuration Protocol (DHCP) if the IRAC were directly
connected to a LAN.
The Configuration payload is defined as follows:
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Payload |C| RESERVED | Payload Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CFG Type | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Configuration Attributes ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 22: Configuration Payload Format
The payload type for the Configuration payload is forty-seven (47).
o CFG Type (1 octet) - The type of exchange represented by the
Configuration Attributes. The values in the following table are
only current as of the publication date of RFC 4306. Other values
may have been added since then or will be added after the
publication of this document. Readers should refer to [IKEV2IANA]
for the latest values.
CFG Type Value
--------------------------
CFG_REQUEST 1
CFG_REPLY 2
CFG_SET 3
CFG_ACK 4
o RESERVED (3 octets) - MUST be sent as zero; MUST be ignored on
receipt.
o Configuration Attributes (variable length) - These are type length
value (TLV) structures specific to the Configuration payload and
are defined below. There may be zero or more Configuration
Attributes in this payload.
3.15.1. Configuration Attributes
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R| Attribute Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Value ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 23: Configuration Attribute Format
o Reserved (1 bit) - This bit MUST be set to zero and MUST be
ignored on receipt.
o Attribute Type (15 bits) - A unique identifier for each of the
Configuration Attribute Types.
o Length (2 octets, unsigned integer) - Length in octets of value.
o Value (0 or more octets) - The variable-length value of this
Configuration Attribute. The following lists the attribute types.
The values in the following table are only current as of the publication date of RFC 4306 (except INTERNAL_ADDRESS_EXPIRY and INTERNAL_IP6_NBNS, which were removed by RFC 5996). Other values may have been added since then or will be added after the publication of this document. Readers should refer to [IKEV2IANA] for the latest values. Attribute Type Value Multi-Valued Length ------------------------------------------------------------ INTERNAL_IP4_ADDRESS 1 YES* 0 or 4 octets INTERNAL_IP4_NETMASK 2 NO 0 or 4 octets INTERNAL_IP4_DNS 3 YES 0 or 4 octets INTERNAL_IP4_NBNS 4 YES 0 or 4 octets INTERNAL_IP4_DHCP 6 YES 0 or 4 octets APPLICATION_VERSION 7 NO 0 or more INTERNAL_IP6_ADDRESS 8 YES* 0 or 17 octets INTERNAL_IP6_DNS 10 YES 0 or 16 octets INTERNAL_IP6_DHCP 12 YES 0 or 16 octets INTERNAL_IP4_SUBNET 13 YES 0 or 8 octets SUPPORTED_ATTRIBUTES 14 NO Multiple of 2 INTERNAL_IP6_SUBNET 15 YES 17 octets * These attributes may be multi-valued on return only if multiple values were requested. o INTERNAL_IP4_ADDRESS, INTERNAL_IP6_ADDRESS - An address on the internal network, sometimes called a red node address or private address, and it MAY be a private address on the Internet. In a request message, the address specified is a requested address (or a zero-length address if no specific address is requested). If a specific address is requested, it likely indicates that a previous connection existed with this address and the requestor would like to reuse that address. With IPv6, a requestor MAY supply the low- order address octets it wants to use. Multiple internal addresses MAY be requested by requesting multiple internal address attributes. The responder MAY only send up to the number of addresses requested. The INTERNAL_IP6_ADDRESS is made up of two fields: the first is a 16-octet IPv6 address, and the second is a one-octet prefix-length as defined in [ADDRIPV6]. The requested address is valid as long as this IKE SA (or its rekeyed successors) requesting the address is valid. This is described in more detail in Section 3.15.3. o INTERNAL_IP4_NETMASK - The internal network's netmask. Only one netmask is allowed in the request and response messages (e.g., 255.255.255.0), and it MUST be used only with an INTERNAL_IP4_ADDRESS attribute. INTERNAL_IP4_NETMASK in a CFG_REPLY means roughly the same thing as INTERNAL_IP4_SUBNET
containing the same information ("send traffic to these addresses
through me"), but also implies a link boundary. For instance, the
client could use its own address and the netmask to calculate the
broadcast address of the link. An empty INTERNAL_IP4_NETMASK
attribute can be included in a CFG_REQUEST to request this
information (although the gateway can send the information even
when not requested). Non-empty values for this attribute in a
CFG_REQUEST do not make sense and thus MUST NOT be included.
o INTERNAL_IP4_DNS, INTERNAL_IP6_DNS - Specifies an address of a DNS
server within the network. Multiple DNS servers MAY be requested.
The responder MAY respond with zero or more DNS server attributes.
o INTERNAL_IP4_NBNS - Specifies an address of a NetBios Name Server
(WINS) within the network. Multiple NBNS servers MAY be
requested. The responder MAY respond with zero or more NBNS
server attributes.
o INTERNAL_IP4_DHCP, INTERNAL_IP6_DHCP - Instructs the host to send
any internal DHCP requests to the address contained within the
attribute. Multiple DHCP servers MAY be requested. The responder
MAY respond with zero or more DHCP server attributes.
o APPLICATION_VERSION - The version or application information of
the IPsec host. This is a string of printable ASCII characters
that is NOT null terminated.
o INTERNAL_IP4_SUBNET - The protected sub-networks that this edge-
device protects. This attribute is made up of two fields: the
first being an IP address and the second being a netmask.
Multiple sub-networks MAY be requested. The responder MAY respond
with zero or more sub-network attributes. This is discussed in
more detail in Section 3.15.2.
o SUPPORTED_ATTRIBUTES - When used within a Request, this attribute
MUST be zero-length and specifies a query to the responder to
reply back with all of the attributes that it supports. The
response contains an attribute that contains a set of attribute
identifiers each in 2 octets. The length divided by 2 (octets)
would state the number of supported attributes contained in the
response.
o INTERNAL_IP6_SUBNET - The protected sub-networks that this
edge-device protects. This attribute is made up of two fields:
the first is a 16-octet IPv6 address, and the second is a
one-octet prefix-length as defined in [ADDRIPV6]. Multiple
sub-networks MAY be requested. The responder MAY respond with
zero or more sub-network attributes. This is discussed in more
detail in Section 3.15.2.
Note that no recommendations are made in this document as to how an
implementation actually figures out what information to send in a
response. That is, we do not recommend any specific method of an
IRAS determining which DNS server should be returned to a requesting
IRAC.
The CFG_REQUEST and CFG_REPLY pair allows an IKE endpoint to request
information from its peer. If an attribute in the CFG_REQUEST
Configuration payload is not zero-length, it is taken as a suggestion
for that attribute. The CFG_REPLY Configuration payload MAY return
that value, or a new one. It MAY also add new attributes and not
include some requested ones. Unrecognized or unsupported attributes
MUST be ignored in both requests and responses.
The CFG_SET and CFG_ACK pair allows an IKE endpoint to push
configuration data to its peer. In this case, the CFG_SET
Configuration payload contains attributes the initiator wants its
peer to alter. The responder MUST return a Configuration payload if
it accepted any of the configuration data, and the Configuration
payload MUST contain the attributes that the responder accepted with
zero-length data. Those attributes that it did not accept MUST NOT
be in the CFG_ACK Configuration payload. If no attributes were
accepted, the responder MUST return either an empty CFG_ACK payload
or a response message without a CFG_ACK payload. There are currently
no defined uses for the CFG_SET/CFG_ACK exchange, though they may be
used in connection with extensions based on Vendor IDs. An
implementation of this specification MAY ignore CFG_SET payloads.
3.15.2. Meaning of INTERNAL_IP4_SUBNET and INTERNAL_IP6_SUBNET
INTERNAL_IP4/6_SUBNET attributes can indicate additional subnets,
ones that need one or more separate SAs, that can be reached through
the gateway that announces the attributes. INTERNAL_IP4/6_SUBNET
attributes may also express the gateway's policy about what traffic
should be sent through the gateway; the client can choose whether
other traffic (covered by TSr, but not in INTERNAL_IP4/6_SUBNET) is
sent through the gateway or directly to the destination. Thus,
traffic to the addresses listed in the INTERNAL_IP4/6_SUBNET
attributes should be sent through the gateway that announces the
attributes. If there are no existing Child SAs whose Traffic
Selectors cover the address in question, new SAs need to be created.
For instance, if there are two subnets, 198.51.100.0/26 and
192.0.2.0/24, and the client's request contains the following:
CP(CFG_REQUEST) =
INTERNAL_IP4_ADDRESS()
TSi = (0, 0-65535, 0.0.0.0-255.255.255.255)
TSr = (0, 0-65535, 0.0.0.0-255.255.255.255)
then a valid response could be the following (in which TSr and
INTERNAL_IP4_SUBNET contain the same information):
CP(CFG_REPLY) =
INTERNAL_IP4_ADDRESS(198.51.100.234)
INTERNAL_IP4_SUBNET(198.51.100.0/255.255.255.192)
INTERNAL_IP4_SUBNET(192.0.2.0/255.255.255.0)
TSi = (0, 0-65535, 198.51.100.234-198.51.100.234)
TSr = ((0, 0-65535, 198.51.100.0-198.51.100.63),
(0, 0-65535, 192.0.2.0-192.0.2.255))
In these cases, the INTERNAL_IP4_SUBNET does not really carry any
useful information.
A different possible response would have been this:
CP(CFG_REPLY) =
INTERNAL_IP4_ADDRESS(198.51.100.234)
INTERNAL_IP4_SUBNET(198.51.100.0/255.255.255.192)
INTERNAL_IP4_SUBNET(192.0.2.0/255.255.255.0)
TSi = (0, 0-65535, 198.51.100.234-198.51.100.234)
TSr = (0, 0-65535, 0.0.0.0-255.255.255.255)
That response would mean that the client can send all its traffic
through the gateway, but the gateway does not mind if the client
sends traffic not included by INTERNAL_IP4_SUBNET directly to the
destination (without going through the gateway).
A different situation arises if the gateway has a policy that
requires the traffic for the two subnets to be carried in separate
SAs. Then a response like this would indicate to the client that
if it wants access to the second subnet, it needs to create a
separate SA:
CP(CFG_REPLY) =
INTERNAL_IP4_ADDRESS(198.51.100.234)
INTERNAL_IP4_SUBNET(198.51.100.0/255.255.255.192)
INTERNAL_IP4_SUBNET(192.0.2.0/255.255.255.0)
TSi = (0, 0-65535, 198.51.100.234-198.51.100.234)
TSr = (0, 0-65535, 198.51.100.0-198.51.100.63)
INTERNAL_IP4_SUBNET can also be useful if the client's TSr included
only part of the address space. For instance, if the client requests
the following:
CP(CFG_REQUEST) =
INTERNAL_IP4_ADDRESS()
TSi = (0, 0-65535, 0.0.0.0-255.255.255.255)
TSr = (0, 0-65535, 192.0.2.155-192.0.2.155)
then the gateway's response might be:
CP(CFG_REPLY) =
INTERNAL_IP4_ADDRESS(198.51.100.234)
INTERNAL_IP4_SUBNET(198.51.100.0/255.255.255.192)
INTERNAL_IP4_SUBNET(192.0.2.0/255.255.255.0)
TSi = (0, 0-65535, 198.51.100.234-198.51.100.234)
TSr = (0, 0-65535, 192.0.2.155-192.0.2.155)
Because the meaning of INTERNAL_IP4_SUBNET/INTERNAL_IP6_SUBNET in
CFG_REQUESTs is unclear, they cannot be used reliably in
CFG_REQUESTs.
3.15.3. Configuration Payloads for IPv6
The Configuration payloads for IPv6 are based on the corresponding
IPv4 payloads, and do not fully follow the "normal IPv6 way of doing
things". In particular, IPv6 stateless autoconfiguration or router
advertisement messages are not used, neither is neighbor discovery.
Note that there is an additional document that discusses IPv6
configuration in IKEv2, [IPV6CONFIG]. At the present time, it is an
experimental document, but there is a hope that with more
implementation experience, it will gain the same standards treatment
as this document.
A client can be assigned an IPv6 address using the
INTERNAL_IP6_ADDRESS Configuration payload. A minimal exchange might
look like this:
CP(CFG_REQUEST) =
INTERNAL_IP6_ADDRESS()
INTERNAL_IP6_DNS()
TSi = (0, 0-65535, :: - FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
TSr = (0, 0-65535, :: - FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
CP(CFG_REPLY) =
INTERNAL_IP6_ADDRESS(2001:DB8:0:1:2:3:4:5/64)
INTERNAL_IP6_DNS(2001:DB8:99:88:77:66:55:44)
TSi = (0, 0-65535, 2001:DB8:0:1:2:3:4:5 - 2001:DB8:0:1:2:3:4:5)
TSr = (0, 0-65535, :: - FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF)
The client MAY send a non-empty INTERNAL_IP6_ADDRESS attribute in the
CFG_REQUEST to request a specific address or interface identifier.
The gateway first checks if the specified address is acceptable, and
if it is, returns that one. If the address was not acceptable, the
gateway attempts to use the interface identifier with some other
prefix; if even that fails, the gateway selects another interface
identifier.
The INTERNAL_IP6_ADDRESS attribute also contains a prefix length
field. When used in a CFG_REPLY, this corresponds to the
INTERNAL_IP4_NETMASK attribute in the IPv4 case.
Although this approach to configuring IPv6 addresses is reasonably
simple, it has some limitations. IPsec tunnels configured using
IKEv2 are not fully featured "interfaces" in the IPv6 addressing
architecture sense [ADDRIPV6]. In particular, they do not
necessarily have link-local addresses, and this may complicate the
use of protocols that assume them, such as [MLDV2].
3.15.4. Address Assignment Failures
If the responder encounters an error while attempting to assign an IP
address to the initiator during the processing of a Configuration
payload, it responds with an INTERNAL_ADDRESS_FAILURE notification.
The IKE SA is still created even if the initial Child SA cannot be
created because of this failure. If this error is generated within
an IKE_AUTH exchange, no Child SA will be created. However, there
are some more complex error cases.
If the responder does not support Configuration payloads at all, it
can simply ignore all Configuration payloads. This type of
implementation never sends INTERNAL_ADDRESS_FAILURE notifications.
If the initiator requires the assignment of an IP address, it will treat a response without CFG_REPLY as an error. The initiator may request a particular type of address (IPv4 or IPv6) that the responder does not support, even though the responder supports Configuration payloads. In this case, the responder simply ignores the type of address it does not support and processes the rest of the request as usual. If the initiator requests multiple addresses of a type that the responder supports, and some (but not all) of the requests fail, the responder replies with the successful addresses only. The responder sends INTERNAL_ADDRESS_FAILURE only if no addresses can be assigned. If the initiator does not receive the IP address(es) required by its policy, it MAY keep the IKE SA up and retry the Configuration payload as separate INFORMATIONAL exchange after suitable timeout, or it MAY tear down the IKE SA by sending a Delete payload inside a separate INFORMATIONAL exchange and later retry IKE SA from the beginning after some timeout. Such a timeout should not be too short (especially if the IKE SA is started from the beginning) because these error situations may not be able to be fixed quickly; the timeout should likely be several minutes. For example, an address shortage problem on the responder will probably only be fixed when more entries are returned to the address pool when other clients disconnect or when responder is reconfigured with larger address pool.3.16. Extensible Authentication Protocol (EAP) Payload
The Extensible Authentication Protocol payload, denoted EAP in this document, allows IKE SAs to be authenticated using the protocol defined in RFC 3748 [EAP] and subsequent extensions to that protocol. When using EAP, an appropriate EAP method needs to be selected. Many of these methods have been defined, specifying the protocol's use with various authentication mechanisms. EAP method types are listed in [EAP-IANA]. A short summary of the EAP format is included here for clarity.
1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Payload |C| RESERVED | Payload Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ EAP Message ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 24: EAP Payload Format The payload type for an EAP payload is forty-eight (48). 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Code | Identifier | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Type_Data... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- Figure 25: EAP Message Format o Code (1 octet) - Indicates whether this message is a Request (1), Response (2), Success (3), or Failure (4). o Identifier (1 octet) - Used in PPP to distinguish replayed messages from repeated ones. Since in IKE, EAP runs over a reliable protocol, the Identifier serves no function here. In a response message, this octet MUST be set to match the identifier in the corresponding request. o Length (2 octets, unsigned integer) - The length of the EAP message. MUST be four less than the Payload Length of the encapsulating payload. o Type (1 octet) - Present only if the Code field is Request (1) or Response (2). For other codes, the EAP message length MUST be four octets and the Type and Type_Data fields MUST NOT be present. In a Request (1) message, Type indicates the data being requested. In a Response (2) message, Type MUST either be Nak or match the type of the data requested. Note that since IKE passes an indication of initiator identity in the first message in the IKE_AUTH exchange, the responder SHOULD NOT send EAP Identity requests (type 1). The initiator MAY, however, respond to such requests if it receives them.
o Type_Data (variable length) - Varies with the Type of Request and
the associated Response. For the documentation of the EAP
methods, see [EAP].
Note that since IKE passes an indication of initiator identity in the
first message in the IKE_AUTH exchange, the responder SHOULD NOT send
EAP Identity requests. The initiator MAY, however, respond to such
requests if it receives them.
4. Conformance Requirements
In order to assure that all implementations of IKEv2 can
interoperate, there are "MUST support" requirements in addition to
those listed elsewhere. Of course, IKEv2 is a security protocol, and
one of its major functions is to allow only authorized parties to
successfully complete establishment of SAs. So a particular
implementation may be configured with any of a number of restrictions
concerning algorithms and trusted authorities that will prevent
universal interoperability.
IKEv2 is designed to permit minimal implementations that can
interoperate with all compliant implementations. The following are
features that can be omitted in a minimal implementation:
o Ability to negotiate SAs through a NAT and tunnel the resulting
ESP SA over UDP.
o Ability to request (and respond to a request for) a temporary IP
address on the remote end of a tunnel.
o Ability to support EAP-based authentication.
o Ability to support window sizes greater than one.
o Ability to establish multiple ESP or AH SAs within a single
IKE SA.
o Ability to rekey SAs.
To assure interoperability, all implementations MUST be capable of
parsing all payload types (if only to skip over them) and to ignore
payload types that it does not support unless the critical bit is set
in the payload header. If the critical bit is set in an unsupported
payload header, all implementations MUST reject the messages
containing those payloads.
Every implementation MUST be capable of doing four-message
IKE_SA_INIT and IKE_AUTH exchanges establishing two SAs (one for IKE,
one for ESP or AH). Implementations MAY be initiate-only or respond-
only if appropriate for their platform. Every implementation MUST be
capable of responding to an INFORMATIONAL exchange, but a minimal
implementation MAY respond to any request in the INFORMATIONAL
exchange with an empty response (note that within the context of an
IKE SA, an "empty" message consists of an IKE header followed by an
Encrypted payload with no payloads contained in it). A minimal
implementation MAY support the CREATE_CHILD_SA exchange only in so
far as to recognize requests and reject them with a Notify payload of
type NO_ADDITIONAL_SAS. A minimal implementation need not be able to
initiate CREATE_CHILD_SA or INFORMATIONAL exchanges. When an SA
expires (based on locally configured values of either lifetime or
octets passed), an implementation MAY either try to renew it with a
CREATE_CHILD_SA exchange or it MAY delete (close) the old SA and
create a new one. If the responder rejects the CREATE_CHILD_SA
request with a NO_ADDITIONAL_SAS notification, the implementation
MUST be capable of instead deleting the old SA and creating a
new one.
Implementations are not required to support requesting temporary IP
addresses or responding to such requests. If an implementation does
support issuing such requests and its policy requires using temporary
IP addresses, it MUST include a CP payload in the first message in
the IKE_AUTH exchange containing at least a field of type
INTERNAL_IP4_ADDRESS or INTERNAL_IP6_ADDRESS. All other fields are
optional. If an implementation supports responding to such requests,
it MUST parse the CP payload of type CFG_REQUEST in the first message
in the IKE_AUTH exchange and recognize a field of type
INTERNAL_IP4_ADDRESS or INTERNAL_IP6_ADDRESS. If it supports leasing
an address of the appropriate type, it MUST return a CP payload of
type CFG_REPLY containing an address of the requested type. The
responder may include any other related attributes.
For an implementation to be called conforming to this specification,
it MUST be possible to configure it to accept the following:
o Public Key Infrastructure using X.509 (PKIX) Certificates
containing and signed by RSA keys of size 1024 or 2048 bits, where
the ID passed is any of ID_KEY_ID, ID_FQDN, ID_RFC822_ADDR, or
ID_DER_ASN1_DN.
o Shared key authentication where the ID passed is any of ID_KEY_ID,
ID_FQDN, or ID_RFC822_ADDR.
o Authentication where the responder is authenticated using PKIX
Certificates and the initiator is authenticated using shared key
authentication.
(page 124 continued on part 6)