Extended Sequence Number (ESN) Addendum to IPsec Domain of Interpretation (DOI) for Internet Security Association and Key Management Protocol (ISAKMP)
Extracted elements (8)
The ESN option exists to permit transmission of very large volumes of data at high speeds over an IPsec Security Association without rekeying to avoid sequence number space exhaustion, addressing the limitations of traditional 32-bit sequence numbers.
Attributes described as Basic MUST NOT be encoded as variable. This applies to the ESN attribute defined in this document.
If an implementation receives a defined IPsec DOI attribute or attribute value that it does not support, an ATTRIBUTES-NOT-SUPPORT SHOULD be sent and the security association setup MUST be aborted.
If an implementation receives any attribute value other than the value for 64-bit sequence numbers, the security association setup MUST be aborted.
A new IPsec Security Association attribute 'Extended (64-bit) Sequence Number' is defined with attribute type value 11 and type Basic (B), for use in IKE Phase II negotiation. The attribute class value 1 indicates use of 64-bit sequence numbers; value 0 is RESERVED.
IANA has allocated an IPsec Security Attribute value for the 'Extended (64-bit) Sequence Number' Attribute Type, assigned value 11. No additional class values will be assigned for this attribute.
The integrity algorithm used with ESP or AH should be secure relative to the number of packets being protected. The SA lifetime may be set to limit the volume of data protected with a single key prior to reaching the 2^64 packet limit imposed by the ESN.
When using ESNs with ESP, it is important to employ an encryption mode that is secure when very large volumes of data are encrypted under a single key. DES in CBC mode is explicitly noted as NOT suitable for use with ESN, because no more than 2^32 blocks should be encrypted under a single DES key in that mode.