Subscriber interfaces are created as 64-bit WAN mode interfaces by default. At the time of creation, the subscriber interface can also be created as a 128-bit WAN mode interface. After the subscriber interface is created, the WAN mode cannot be changed. To change the WAN mode, the 64-bit subscriber interface must be removed and then recreated as 128-bit. This section describes the differences between 64-bit and 128-bit WAN modes.
In a 64-bit WAN mode subscriber interface, the following rules apply.
The system differentiates each subscriber using only the first 64 bits of the WAN address (each host must have a unique /64 prefix, with the exception of bridge host.) This differentiation includes the ability to identify individual subscribers and to apply different subscriber profile and SLA-profiles to each subscriber.
For IPoE bridge hosts, when a group of hosts shares a prefix, all hosts must share the same SLA-profile.
Each SLAAC subscriber must use a unique /64 prefix. IPoE bridge hosts can share the same SLAAC prefix and must also share the same SLA-profile.
Each IPv6 data-trigger host must use a unique /64 prefix.
The DHCPv6 server must be set up to assign each host with a unique /64 prefix. The 7750 SR local DHCP server assigns each subscriber with a unique /64 prefix by default.
64-bit WAN mode is applicable in deployment models where each subscriber is assigned a unique /64 WAN-prefix which can be used for DHCP or SLAAC.
In a 128-bit WAN mode subscriber interface, the following rules apply.
It is not recommended to change a subscriber interface from unnumbered to numbered (or the other way around). If the subscriber interface must be changed, all ESM hosts under the subscriber should be removed first.
The system can uniquely identify each subscriber using the full 128-bit WAN address. Each 128-bit WAN host can have its own unique SLA and Subscriber profile.
When provisioning a numbered subscriber interface, an IPv6 address or a prefix can be assigned. The mask for the address can range from 32 to 127. If the mask is less than 96, an internal /96 route is generated when a WAN host is created (by DHCP IPv6 IANA). This automatically-generated /96 route is used for subscriber lookup. These /96 routes are visible in the RIB and occupy a route entry in the system forwarding table. A /96 route can serve approximately 4.2 billion WAN hosts. Therefore, a single /96 prefix or address should be able to accommodate all WAN hosts terminating on a subscriber interface. Nokia recommends, when using 128-bit WAN mode to configure subscriber interface, use addresses or prefixes with a mask length of 96 to 127. When using 128-bit WAN mode, it is not recommended to assign individual subscribers unique /64 prefixes, because the system generates an internal /96 route for each host, therefore overloading the routing table.
Adding and removing a prefix or address from the subscriber interface in 128-bit WAN mode may trigger /96 routes to be generated or deleted, which can impact subscriber service. Nokia recommends performing this action during off-peak hours.
The auto-generated /96 routes needed for subscriber lookup are tagged in the RIB as "Wan Mode 128 Route".
# show router 2000 route-table ipv6 2001:db8:2000:100::/96 extensive
===============================================================================
Route Table (Service: 2000)
===============================================================================
Dest Prefix : 2001:db8:2000:100::/96
Protocol : LOCAL
Age : 00h06m26s
Preference : 0
Wan Mode 128 Route : Yes
Next-Hop : N/A
Interface : sub-int-2
QoS : Priority=n/c, FC=n/c
Source-Class : 0
Dest-Class : 0
Metric : 0
ECMP-Weight : N/A
-------------------------------------------------------------------------------
No. of Destinations: 1
===============================================================================
These routes can be leaked between local VPRN services on the same router using MP-BGP export and import policies as they are needed for subscriber lookup in extranet topologies. The auto-generated /96 routes are not advertised in the BGP RIB; instead, the prefix configured on the subscriber interface should be used in BGP.
128-bit WAN mode is supported in unnumbered subscriber interfaces. Each WAN host generates a /128 route.
The allow-unmatching-prefixes command can be performed on a numbered subscriber interface in 128-bit WAN mode. This functionality can be used as a subnet migration tool, but must be performed without hosts under the subscriber interface. Changing a subscriber interface from numbered to unnumbered (or the other way around) impacts subscriber service.
IPv6 DHCP IANA subscribers can be assigned incremental 128-bit addresses.
IPoE-bridge mode is only recommended to be configured with 64-bit WAN mode. For 128-bit WAN mode, the system generates at least one /96 prefix per subscriber to help lookup. Because each subscriber interface has a limited number of allowed prefixes, generating a /96 per subscriber reduces scalability. If 128-bit WAN mode is used, each DHCP IANA host can have a distinct SLA profile. In 64-bit WAN mode, all DHCP IANA hosts must share the same SLA profile.
For IPoE bridge SLAAC hosts, hosts sharing the same /64 prefix must share the same SLA profile. IPoE bridge SLAAC hosts do not differ from 128-bit or 64-bit WAN mode.
Each IPv6 data-trigger host can use a unique /128 address.
The DHCP IA_NA host for both PPPoE and IPoE hosts can assign incremental 128-bit addresses.
For retail VPRN that requires 128-bit WAN mode support, the wholesale subscriber interface must also be configured with 128-bit WAN mode.
SLAAC hosts and DHCP WAN hosts must not share the same prefix.
The following host types are not supported:
GTP hosts
hybrid access hosts
WLAN hosts
default hosts