ESM 128-bit Mode for DHCPv6 IA_NA WAN Hosts

The information and configuration in this chapter are based on SR OS Release 16.0.R4 and cover both IPoE and PPPoE subscribers.

Basic knowledge of ESM is a prerequisite.

Nokia Triple Play Service Delivery Architecture (TPSDA) supports both 64-bit and 128-bit WAN mode. This chapter describes 64-bit and 128-bit WAN mode for DHCPv6 IA_NA WAN hosts and provides an example 128-bit WAN mode subscriber interface configuration for IPoE IPv6 hosts.

The 64-bit and 128-bit WAN mode is a creation time configurable parameter on the subscriber interface. The parameter specifies the host addressing schema for a DHCPv6 WAN host (DHCPv6 IA_NA). By default, all subscriber interfaces use the 64-bit WAN mode. This means that each WAN host created on the system would consume an entire /64 prefix. More specifically, the WAN host would construct only one 128-bit address out of the entire /64 prefix. By comparison, the 128-bit WAN mode allows a single 128-bit address for each DHCPv6 WAN host. Therefore, when using DHCPv6 IA_NA, the 128-bit WAN mode reduces IPv6 address consumption. All ESM features are supported regardless of the configured WAN mode.

In 64-bit mode, the subscriber interface expects all WAN hosts to have /64 unique prefixes. The system will only distinguish individual IPv6 subscribers by the first 64 bits of an IPv6 address. When IPv6 WAN addresses are /64 unique, a WAN host consumes an entire /64 prefix (with the exception of IPoE-bridged mode, described later). For example, if the first IPv6 WAN host is assigned an DHCPv6 IA_NA address of 2001::1, the next address must be a 64-bit increment. Therefore, the second IPv6 WAN host must be assigned a DHCPv6 IA_NA address of 2001:0:0:1::1. In this mode, all WAN hosts are assigned a /64 prefix regardless of whether the host is using SLAAC or DHCPv6. This provides the flexibility for allowing the subscriber to choose between using SLAAC or DHCPv6 when assigned a /64 prefix.

The 128-bit mode allows the system to distinguish individual IPv6 WAN hosts using the full 128-bit address. For example, if the first IPv6 WAN host is assigned an address of 2001::1, the next host address can be a 128-bit increment, which is 2001::2. Compared to 64-bit mode, a single WAN host no longer consumes an entire /64 prefix. When the system is operating in 128-bit mode, a /96 prefix is automatically created in the FIB to assist in subscriber host lookup. Therefore, in 128-bit mode, subnets using a prefix length of 96 or longer are recommended. Within a /96 subnet, about 4 billion IPv6 addresses (WAN hosts) can be supported.

Extra considerations are required for subscriber interfaces operating in 128-bit mode.

• All subscribers within a subscriber interface should use a single /96 prefix (or longer; for example, /97).

• In the case where multiple prefixes are required (for example, service differentiation), Nokia recommends keeping the number of /96 prefixes to a minimum.

• The 128-bit WAN mode can support SLAAC hosts. The system will not derive a /96 prefix from the SLAAC host. However, the system does not allow a SLAAC host and a DHCPv6 IA_NA host to share the same subscriber interface prefix. SLAAC hosts must use a different prefix than a DHCPv6 IA_NA host.

• The routing instance (VPRN or IES) supports a mixture of 64-bit and 128-bit WAN mode subscriber interfaces.

The local DHCPv6 server supports assigning both incremental DHCP IA_NA /64 and /128 addresses. The local DHCP server will determine which subscriber interface the DHCP IA_NA request is from. With this information, the server will automatically determine whether the next incremental /64 or /128 address should be assigned. There is no configuration required on the local DHCP server; this is performed automatically by the server.

In addition, it is possible to use the local DHCP server for DHCPv6 IA_NA address assignment while using AAA for DHCPv6 IA_PD prefix assignment. For this, the local address assignment feature is required (configured under group-interface). The client application is IPoE WAN and the DHCPv6 IA_NA address is assigned via a pool name retrieved from AAA or LUDB. The local address assignment also supports incremental /64 and /128 address assignment. This is also determined automatically by the local DHCP server without requiring any additional configuration.

For IPoE-bridged mode, Nokia recommends using only the 64-bit WAN mode. IPoE-bridged mode allows a single subscriber up to 128 bridge hosts sharing the same /64 prefix. Nokia does not recommend using 128-bit WAN mode when IPoE bridging is required. This is due to the 128-bit WAN mode generating at least one /96 prefix per subscriber. There is a limit of prefixes supported per subscriber interface. In 64-bit WAN mode, the subscriber is assigned an entire /64 prefix, but the mode allows each host to have an incremental 128-bit address.

Table 1 compares the 64-bit WAN mode with the 128-bit WAN mode.

Table 1. 64-bit WAN Mode Versus 128-bit WAN Mode

	64-bit WAN mode	128-bit WAN mode	Comments
IPv6 WAN hosts	IPv6 WAN hosts must be assigned 64-bit incremental addresses.	IPv6 WAN hosts can be assigned 128-bit incremental addresses.
DHCPv6 local-dhcp-server	Automatically assigns incremental /64 addresses to DHCP IA_NA requests.	Automatically assigns incremental /128 addresses to DHCP IA_NA requests.	Requires no configuration.
Local-address-assignment for DHCPv6 IA_NA	Automatically assigns incremental /64 addresses to DHCP IA_NA requests.	Automatically assigns incremental /128 addresses to DHCP IA_NA requests.	Local address assignment is used when the local DHCP server is used to assign the DHCPv6 IA_NA addresses while AAA assigns the DHCPv6 IA_PD addresses.
IPoE-bridged-mode	Supported. Recommended mode. Up to 128 bridge hosts can share the same /64 prefix. All bridge hosts must share the same SLA profile.	Supported. Not recommended mode. Up to 128 bridge hosts can share the same /64 prefix. DHCPv6 IA_NA hosts can have unique SLA profiles SLAAC hosts must share the same SLA profile.
FIB	No FIB impact.	A host creation will automatically install a /96 FIB entry. Hosts that share the same /96 will not create new FIB entries. If all hosts within the same /96 entry are removed from the system, the /96 FIB entry will automatically be removed.	128-bit WAN mode can impact FIB scaling if used incorrectly. 128-bit WAN mode is intended for deployments where all WAN hosts under a single subscriber interface share a /96 prefix (or smaller). A /96 prefix can serve up to 4 billion WAN subscribers.

Create a 128-bit WAN mode subscriber interface for IPoE IPv6 hosts.

As already indicated, the WAN mode is a creation-time parameter. It is not possible to toggle between 64-bit and 128-bit mode once the subscriber interface is created.

1. Create a subscriber interface as a 128-bit WAN mode interface, as follows:

   
   *A:BNG-1>config>service>ies# info 
   ----------------------------------------------
               description "BNG-1"
               subscriber-interface "sub-int-1" wan-mode mode128 create
   

2. Following is the rest of a subscriber management configuration on the BNG. For 128-bit WAN mode, the prefix length for the WAN host is 96. Nokia recommends using prefix length 96 or longer when using 128-bit WAN mode.

   
   *A:BNG-1>config>service>ies# info 
   ----------------------------------------------
               description "BNG-1"
               subscriber-interface "sub-int-1" wan-mode mode128 create
                   address 10.255.255.253/8
                   ipv6
                       subscriber-prefixes
                           prefix 2001:db8::/96 wan-host
                       exit
                   exit
                   group-interface "group-int-1" create
                       dhcp
                           server 192.168.0.1
                           lease-populate 10
                           client-applications dhcp
                           gi-address 10.255.255.253
                           no shutdown
                       exit
                       ipv6
                           dhcp6
                               proxy-server
                                   no shutdown
                               exit
                               relay
                                   link-address 2001:db8::
                                   server 2001:db9::1
                                   client-applications dhcp 
                                   no shutdown
                               exit
                           exit
                       exit
                       sap 1/1/5:4 create
                           sub-sla-mgmt
                               def-sub-id use-sap-id
                               def-sub-profile "sub-profile-1"
                               def-sla-profile "sla-profile-1"
                               sub-ident-policy "sub-ident-policy-1"
                               multi-sub-sap 10
                               no shutdown
                           exit
                       exit
                   exit
               exit
   

   With the preceding configuration, the subscriber interface is ready to support 128-bit incremental IPv6 address assignment, as follows:

   
   *A:BNG-1> show  service active-subscribers hierarchy
    
   ===============================================================================
   Active Subscribers Hierarchy
   ===============================================================================
   -- sub_1 (sub-profile-1)
      |
      +-- sap:1/1/5:4 - sla:sla-profile-1
          |
          +-- IPOE-session - mac:00:00:10:10:13:13 - svc:1
              |
              +-- 2001:db8::1/128 - DHCP6
    
   -- sub_2 (sub-profile-1)
      |
      +-- sap:1/1/5:4 - sla:sla-profile-1
          |
          +-- IPOE-session - mac:00:00:10:10:13:14 - svc:1
              |
              +-- 2001:db8::2/128 - DHCP6
    
   -------------------------------------------------------------------------------
   Number of active subscribers : 2
   Flags: (N) = the host or the managed route is in non-forwarding state
   ===============================================================================   
   

   If the subscriber interface is in 64-bit WAN mode, the system will reject a subsequent subscriber host that requests addresses that overlap with the /64 prefix of existing hosts, as follows:

   
   *A:eng-BNG-2>config>service>vprn>sub-if>grp-if>ipv6# show log log-id 99
    
   ===============================================================================
   Event Log 99
   ===============================================================================
   Description : Default System Log
   Memory Log contents  [size=500   next event=367512  (wrapped)]
    
   367507 2018/09/19 20:18:37.656 UTC WARNING: DHCP #2005 IES1 Lease State Population Error
   "Lease state table population error on SAP 1/1/5:4 in service 1 - Host with IP 2001:db8::2/128 and MAC 00:00:10:10:13:14 conflicts with existing host in service 1"
   ===============================================================================   
   

Different operators have unique IPv6 WAN addressing requirements. The 64-bit WAN mode is most suitable for assigning a /64 prefix to a subscriber (WAN host). This mode gives the subscriber flexibility to either use the /64 prefix for SLAAC or one address out of the /64 prefix for a DHCPv6 IA_NA address. The 128-bit WAN mode is for operators who prefer to use DHCPv6 IA_NA addressing. With 128-bit mode, each subscriber is assigned a single 128-bit address, minimizing IPv6 WAN address consumption. By using different WAN modes, addressing scaling and efficiency can be improved.