Obtaining MAP-T/MAP-E IPv6 Prefixes

IPv6 Prefix Allocation Methods

BRASs can only use DHCPv6 IA_PD, not ND, to assign IPv6 prefixes to MAP-T and MAP-E users.

MAP-T/MAP-E User Identification

When a MAP-T or MAP-E user performs a DHCPv6 dialup, a DHCPv6 Request message must be sent to request a matching MAP option (Option 94 or 95) in the ORO option.

Option 94 identifies a MAP-E user, and option 95 identifies a MAP-T user. If a user requests both Options 94 and 95, the MAP-E user is preferentially identified by default, and a MAP-E IPv6 prefix is assigned. If a MAP-E IPv6 prefix fails to be assigned to the user, a MAP-T IPv6 prefix is assigned. The MAP-T user can be assigned a higher priority in a MAP domain.

MAP Option Encapsulation

After a BRAS assigns IPv6 prefixes to MAP-E and MAP-E users, the BRAS sends DHCPv6 Response messages carrying Option 94 (MAP-E) or Option 95 (MAP-E) and the other MAP parameters to the users.

Option 94 (OPTION_S46_CONT_MAPE)

Option 94 identifies only a MAP-E user, and its format is as follows:

The option code field value is 94, and the option-length field is a variable and depends on the effective packet size.
encapsulated-options: the sub-options of Option 94 of the MAP-E user. These sub-options include Options 89, 90, and 93.

Figure 1 Option 94

Option 95 (OPTION_S46_CONT_MAPT)

Option 95 identifies only a MAP-T user, and its format is as follows:

The option code field value is 95, and the option-length field is a variable and depends on the effective packet size.
encapsulated-options: the sub-options of Option 95 of the MAP-E user. These sub-options include Options 89, 91, and 93.

Figure 2 Option 95

Option 89 (OPTION_S46_RULE)

Option 89 can be encapsulated in packets for both MAP-E and MAP-T users. Option 89 is a sub-option of Options 94 and 95 and its format is as follows:

Figure 3 Option 89

The option code field value is 89, and the option-length field is a variable and depends on the effective packet size.
flags: shows the format. The reserved bit is 0. The default F bit value is 1, and the F bit can be 0 if the option-s46 fmr-flag disable command is run in an address pool.
ea-len: is obtained from a mapping rule referenced by a prefix pool. The value can be set.
prefix4-len and ipv4-prefix: are obtained from a mapping rule referenced by a prefix pool. The values can be set. The ipv4-prefix field is fixed at 4 bytes, and the prefix4-len field is padded with 0s.
prefix6-len and ipv6-prefix: are obtained from a mapping rule referenced by a prefix pool. The values can be set. If the prefix6-len value cannot be divided by eight with no remainder, the ipv6-prefix value must be padded with 0s to be a multiplier of eight, whereas the prefix6-len value remains.
S46_RULE-options: is Option 93 that is a sub-option of Option 89.

Option 93 (OPTION_S46_PORTPARAMS)

Option 93 can be encapsulated in packets for both MAP-E and MAP-T users. Option 93 is a sub-option of Options 94 and its format is as follows:

Figure 4 Option 93

The option code field value is 93, and the option-length field fixed at 4 bytes.
offset: is obtained from a mapping rule referenced by a prefix pool. The value can be set.
PSID-len and PSID: used in the following scenarios:
- ea-len + prefix4-len < 32: Both PSID-len and PSID values are 0, and IPv4 prefixes are assigned to MAP users.
- ea-len + prefix4-len = 32: Both PSID-len and PSID values are 0, and an exclusive IPv4 address is assigned to each MAP user.
- ea-len + prefix4-len > 32: The PSID-len field value is (ea-len + prefix4-len - 32). The PSID (16-bit, suffixed with zeros if less than 16 bits) is the last "PSID-len" bit in a PD prefix of a MAP user. A shared IP address is assigned to a MAP user, and the IPv4 port is computed based on the PSID.

Option 90 (OPTION_S46_BR)

Option 90 identifies only a MAP-E user. It is a sub-option of Option 94 and its format is as follows:

Figure 5 Option 90

The option code field value is 90, and the option-length field fixed at 16 bytes.
br-ipv6-address: is encapsulated based on the option-s46 br-ipv6-address command run in an address pool. The value is fixed at 16 bytes. If a mask length is 128 bits, a unicast address is used. If a mask length is less than 128 bits, an anycast address is used, and 0s are padded on the right of the mask.

Option 91 (OPTION_S46_DMR)

Option 91 identifies only a MAP-T user. It is a sub-option of Option 95 and its format is as follows:

Figure 6 Option 91

The option code field value is 91, and the option-length field is a variable and depends on the effective packet size.
dmr-prefix6-len and dmr-ipv6-prefix: are encapsulated based on the option-s46 dmr-prefix command run in an address pool. If the dmr-prefix6-len value cannot be divided by eight with no remainder, the dmr-ipv6-prefix value must be padded with 0s to be a multiplier of eight, whereas the dmr-prefix6-len value remains.