RFC 2464 Transmission of IPv6 Packets over Ethernet NetWorks
Overview
This RFC mainly describes some of the relevant specifications definitions that transmit IPv6 messages on Ethernet. These specifications mainly cover the method of frame format, constructing IPv6 link-local address, and stateless autoconfigured address, and also define routing, routing advertisements, neighbor, neighbor notice, and redirect packets. The content of the source / destination link layer address option.
Maximum Transmission Unit (MTU)
For IPv6 messages on Ethernet, the default MTU is 1500, which can also be set by routing notices or manually configured (including DHCP mode). When a routing notification with the MTU option is received, the value of the MTU specified in the message should be determined. This value is used if the value is less than 1500. This option is ignored if the value is greater than 1500 or greater than manually configured, and the option is ignored and recorded in the system management log.
Frame format
When IPv6's packet is transmitted on Ethernet, it is packaged in an Ethernet head in a marked. The Ethernet head includes a destination address, source address, and type code. The format is arranged as follows:
Destination Ethernet Address - 16BITS * 3
Source Ethernet Address - 16Bits * 3
Ethernet Type - 16Bits = 0x86DD
IPv6 header and payload
No state automatic configuration
The interface ID of the Ethernet interface is identified based on the EUI-64 (64-bit Extended Unique Identifier). The EUI-64 identifier of the NIC is extended by the 48-bit IEEE 802 address built by the NIC. Next, the construction method of EUI-64 is described below.
The ORGANIZATIONALLE UNIQUE Identifier section of the Ethernet address (ie the first 3 bytes) constitutes the company_ID portion of the EUI-64 (ie the first 3 bytes), the fourth and fifth bytes of the EUI are fixed 16. Value fffe. The last three bytes of the Ethernet address constitute the last 3 bytes of EUI-64.
The interface identifier is derived by using the "global / local" ("unive / local") of EUI-64. This bit is the second low position of the first byte of EUI-64. Since the built-in address of the NIC is allocated globally, the identity obtained is also unique worldwide. The bit of the IEEE 802 or EUI-64 address is 0, and the global unique IPv6 interface identifies this bit of 1.
For example, a MAC address of a network card is: 34-56-78
-9a
-Bc-de, then its corresponding interface identification should be: 36-56-78-FF-Fe
-9a
-Bc-de.
For manual setting or software settings, the interface ID should not be used to construct the interface ID. If you must use such an address to construct an interface identifier, you should reflect whether the address is uniquely on the "U / L" bit.
The length of the IPv6 address prefix (IPv6 Address Prefix) used for an Ethernet card is automatically configured (IPv6 Address Prefix) must be 64 bits.
Link-local address
The IPv6 Link-Local Address of the Ethernet card is constructed by the interface identifier of the interface. The constructor is: the highest 10 bit is "1111111010", and the 54 bit is all 0, and the last 64 bit is the interface identifier of the interface.
For example, interface identification is: 36-56-78-FF-Fe
-9a
-Bc-de, then the corresponding IPv6 link-local address is: fe80 :: 3656: 78ff: Fe9a
: Bcde.
Address mapping - unicast
The map of the IPv6 unicast address to the link layer address is described in detail in RFC2461 (Neighbor Discovery). For Ethernet, the format of the source / destination link layer address option is as follows:
TYPE: 8BITS - 1 is the source link layer address, 2 is the destination link layer address.
Length: 8BITS - 1 (in 8 bytes).
Ethernet Address: 48Bits - Ethernet address.
Address mapping - multicast
Packets with IPv6 multicast addresses, the structure of the corresponding recipient's Ethernet multicast address is: the first two bytes are 16 credits 3333, the remaining 4 bytes are the IPv6 multicast of the message The last 4 bytes of the address.
Safe consideration
The interface identifier is to ensure global uniqueness via the MAC address. But there is no protection mechanism to ensure that the address does not conflict with coincidence or forgery.
