This section examines an example MAP-T deployment with three MAP rules. The deployment assumes the following:
There are about 12,000 private IPv4 addresses that need to be translated via MAP-T.
Each such address should have approximately 4000 ports available per CE. Therefore, the IP address sharing ratio is 16:1; that is, 16 CEs share the same public IP address.
The public IPv4 addresses that are available to the operator for this translation are from three /24 subnets (10.11.11.0/24, 10.12.12.0/24 and 10.13.13.0/24).
All users (or CEs) are assigned a /60 IA-PD.
The 12,000 private IPv4 addresses (CEs) in a 16:1 sharing scenario can be covered using three /24 subnets as follows:
(3 * 2^8 * 16 = 12,288)
The IPv4 rule prefix and EA bits length per rule in this scenario are:
10.11.11.0/24 EA length: 12 bits (8 bits for the IPv4 suffix and 4 bits for PSID)
10.12.12.0/24 EA length: 12 bits (8 bits for the IPv4 suffix and 4 bits for PSID)
10.13.13.0/24 EA length: 12 bits (8 bits for the IPv4 suffix and 4 bits for PSID)
The first 6 bits of the 16 bit port-range are set to 000000 and are reserved for psid-offset (ports 0-1023 are reserved); therefore, the user-allocated port space is calculated as follows:
4000 - 64 = 4032 ports
The IPv6 rule prefix is the next parameter in the MAP rule. Figure: Determining the rule IPv6 prefix shows the relevant bits in the IPv6 address: only bits /32 to /64 are considered; the irrelevant bits of the IPv6 addresses are ignored in this example.
The following three rules are created in this example:
Rule 1 covers subnet 1.
Rule 2 covers subnet 2.
Rule 3 covers subnet 3.
In each of the three cases, the EA bits extend from the PD length (/60) to the IPv6 rule prefix length (/48).
The IPv6 rule prefix length is determined for each of the three rules. However, the IPv6 rule prefixes must not overlap, see sectionRule prefix overlap for more information. Non-overlapping IPv6 rule prefixes ensure that each CE is assigned a unique IA-PD. Table: IPv6 rule prefixes describes the rules.
|
Rule 1 | Rule 1 | Rule 1 |
|---|---|---|---|
IPv6 rule prefix |
2001:db8:0000::/48- |
2001:db8:0001::/48- |
2001:db8:0002::/48- |
IPv4 rule prefix |
10.11.11.0/24 |
10.12.12.0/24 |
10.13.13.0/24 |
EA bits |
12 |
12 |
12 |
Paid-Offset |
6 |
6 |
6 |
The final step is to ensure that the DHCPv6 server hands out correct end-user prefixes (IA-PD), and the rules are also delegated.
In this example, each /48 IPv6 rule prefix supports 4,000 MAP-T CEs, where each CE can further delegate 15 IPv6 ‟subnets” on the LAN side and each CE is allocated about 4,000 ports to use in stateful NAT44.