To support allocations of unique IP addresses each ISA is assigned pools from a centralized pool manager on the CPM. The ISA can subsequently assign addresses from these pools to UEs, but this state is not synchronized back to the CPM. Different applications have different pools, for example, SLAAC and DHCPv6 IA_NA cannot share a single pool. To support Wholesale/Retail scenarios a pool-manager can be configured per subscriber interface.
The allocation of additional pools and freeing up unused pools is based on configurable high and low watermarks. When the usage level of all pools combined on an ISA reaches the high watermark, a new pool is allocated. When the usage level of a single pool reaches zero and the usage level of the other pools combined is below the low watermark, this pool is freed.
With redundancy, the pool manager signals the pools that were allocated to the failed ISA back to the new active ISA. These pools can no longer be used to allocate new addresses because allocations are lost. However, these can still be used to forward traffic based on data-triggered UE creation. This is supported both for IOM redundancy and Active/Standby WLAN-GW redundancy. The new active ISA also receives new pools that it can use for new allocations.
The pool manager uses DHCPv6 Prefix Delegation to allocate pools to the ISAs. Each ISA is represented by a separate DHCPv6 Client ID. These clients request fixed prefix sizes to accommodate up to 64K UEs. With Active/Standby redundancy the Pool Manager uses a DHCPv6 Lease Query Message to retrieve the prefixes that were allocated to the failed WLAN-GW. To identify the correct PD leases in the DHCPv6 server, a configurable virtual-chassis-name is added to the DHCPv6 client-id, this value should be identical on both WLAN-GWs and unique otherwise. The Pool Manager always sends out a DHCPv6 Relay message and supports up to eight DHCPv6 servers.
IPv4 pools are supported by encoding an IPv4 subnet into an IPv6 prefix. The least significant 32 bits of the prefix are treated as an IPv4 address and the allocated prefix-length is subtracted with 96 to obtain an IPv4 prefix length. It is recommended to use the special IPv6 prefix ‟::ffff:/96” to provision these pools.
A:system>config>subscr-mgmt>wlan-gw# info
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virtual-chassis-identifier "wlan_gw_pair"
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A:system>config>service>vprn>sub-if>wlan-gw# info
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pool-manager
watermarks high 85 low 66
wlan-gw-group 1
dhcpv6-client
server 2001:db8::1
lease-query max-retry 2
slaac
pool-name "pool_ue_pd_v6_slaac"
no shutdown
exit
ia-na
pool-name "pool_ue_pd_v6_dhcp6"
no shutdown
exit
dhcpv4-nat
pool-name "pool_ue_pd_v6_dhcp4_nat"
no shutdown
exit
exit
exit
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