Transmission of IPv6 via the IPv6 Convergence Sublayer over IEEE 802.16 Networks
updated by
- rfc-8064 — Recommendation on Stable IPv6 Interface Identifiers
Extracted elements (27)
In WiMAX networks, the recommended MTU for IPv6 is 1400 octets rather than the default 1500, because GRE tunnel overhead between BS and AR plus the 6-byte 802.16 MAC header would cause fragmentation of 1500-byte packets. This value must be communicated to the MS via the RA MTU option.
The MaxRtrAdvInterval and router lifetime are set to very large values (default 10800 seconds) in 802.16 to avoid waking mobile stations that are in idle mode, in which the radio link is torn down and paging is required to deliver packets. Frequent RAs would waste air interface resources.
The point-to-point link model for IPv6 over 802.16 is used because each MS is connected to the AR via a unique CID-identified transport connection, making each MS belong to a separate subnet. This model is fully consistent with RFC 4861's definition of a point-to-point link.
Use of router advertisements for movement detection is not recommended for MNs connected via 802.16 links because the frequency of periodic RAs would need to be impractically high. Instead, link triggers or other means are preferred for detecting attachment changes.
IPv6 support over IP CS is indicated by Bit #2 of the CS capability parameter in REG-REQ/REG-RSP messages. By default, Packet, IPv4, and 802.3/Ethernet are supported; absence of this parameter implies only those defaults, not IPv6 over IP CS.
This specification covers only IPv6 over the IP-specific part of the Packet CS (IP CS). Transmission of IP over Ethernet over 802.16 is specified separately in [IPoE-over-802.16], and IPv4 over IP CS is specified in [IPv4-over-IPCS].
A unique IPv6 prefix (or prefixes) MUST be assigned to each link (MS/host). The point-to-point link model requires per-MS prefix assignment; a different prefix should be assigned to each unique link.
BS implementations are REQUIRED to support all standards-track encapsulations defined for 802.16 by the IETF, to ensure interoperability between devices supporting different encapsulations.
DAD SHOULD be performed as per RFC 4861 and RFC 4862. However, DAD on a global unicast address may be redundant if (1) the AR assigns unique prefixes per link and (2) the AR does not autoconfigure IPv6 global unicast addresses from the advertised prefix.
Every Internet host connected via an 802.16 link MUST be able to send and receive IPv6 packets via IP CS when the MS and BS indicate IPv6 protocol support over IP CS.
MLDv2 (RFC 3810) SHOULD be supported by hosts and routers attached via an 802.16 link. The AR SHOULD NOT send periodic MLD queries if the host is in idle/dormant mode, using paging controller state information to determine host status.
The AdvDefaultLifetime (router lifetime) in router advertisements MUST be either zero or between MaxRtrAdvInterval and 43200 seconds. The default value is 2 * MaxRtrAdvInterval. This overrides the RFC 4861 specification.
The default MTU for IPv6 packets over an 802.16 link SHOULD be 1500 octets. If a value different from 1500 is used, the AR MUST advertise the MTU value via the MTU option in router advertisements as defined in RFC 4861.
The MaxRtrAdvInterval MUST be no less than 4 seconds and no greater than 21600 seconds. The default value for MaxRtrAdvInterval is 10800 seconds, overriding RFC 4861's recommendation.
The MS and BS MUST negotiate at most one convergence sublayer for IPv6 transport on a given link. Failure to negotiate a common CS results in failure to set up the transport connection.
The MS MUST request the establishment of a service flow for IPv6 packets over IP CS if the MS and BS have confirmed capability for supporting IPv6 over IP CS. The service flow MAY also be triggered by the network via pre-provisioning.
The MS MUST use its 48-bit globally unique MAC address (as specified in 802.16) to generate a modified EUI-64 format-based interface identifier as specified in RFC 4291. Other mechanisms such as random interface identifiers per RFC 4941 MAY also be used.
When stateful address autoconfiguration is performed, it MUST be performed as specified in RFC 4861 and RFC 3315 (DHCPv6).
When stateless address autoconfiguration is performed, it MUST be performed as specified in RFC 4861 and RFC 4862.
When the MS and BS indicate IPv6 protocol support over both IP CS and Ethernet CS, the MS and BS MUST use IP CS for sending and receiving IPv6 packets, making IP CS the default and preferred mode.
In WiMAX, the IPv6 link is formed by combining (1) a CID-identified transport connection over the 802.16 air interface between MS and BS, and (2) a GRE tunnel between BS and AR/ASN-GW. From IPv6's perspective, MS and AR are connected by a single point-to-point link.
One or more /64 prefixes SHOULD be assigned to each 802.16 link (MS). Prefixes are advertised with the on-link (L-bit) flag set. DHCP or AAA-based prefix delegation MAY be used to provide one or more prefixes for an AR connected over 802.16.
The IP-specific part of the Packet Convergence Sublayer (IP CS) is the mechanism by which IPv6 packets are transported directly over the IEEE 802.16 MAC. The Packet CS classifiers differentiate IPv4 and IPv6 packets and map them to specific transport connections identified by a Connection Identifier (CID).
The IPv6 link in 802.16 is defined as the collection of transport connections (CIDs) and, when the AR is separate from the BS, GRE tunnels between BS and AR. The granularity of the GRE tunnel SHOULD be no greater than per-MS or per-service-flow. Each MS belongs to a distinct point-to-point link.
This document does not introduce new vulnerabilities to IPv6 operation. The 802.16 air interface provides traffic encryption using a Traffic Encryption Key (TEK) generated by the MS and BS on successful authentication. IPv6 security mechanisms (e.g., IPsec) may be used in addition to 802.16 link-layer security.
IPv6 link establishment in 802.16 follows a sequential procedure: (1) initial ranging/synchronization, (2) SBC-REQ/RSP basic capability exchange, (3) PKMv2-based authentication, (4) 802.16 registration, (5) REG-REQ/RSP capability exchange with IPv6 CS capability indicated by Bit #2, (6) service flow establishment for IPv6 over IP CS, (7) router advertisement/solicitation exchange.
IPv6 packets carried over the IP CS are encapsulated by a 6-byte IEEE 802.16 Generic MAC header. An optional CRC covers the header and payload. The actual MAC address is not included in the MAC header; the Len field in the header is 11 bits, giving a total MAC PDU size of 2048 bytes.