DHCPv6

The call flows for DHCPv6 lease split are similar to DHCPv4 lease split.

As shown in the following output, in a single DHCPv6 transaction, both IA_NA and IA_PD Identity Association (IA) types can be present, each with their associated timers (renew time T1, rebind time T2, preferred lifetime, and valid lifetime).

 Option : IA_NA (3), Length : 40
         IAID : 0
         Time1: 1800 seconds
         Time2: 2880 seconds
         Option : IAADDR (5), Length : 24
           Address : 2001:db8:100::1
           Preferred Lifetime : 3600 seconds
           Valid Lifetime     : 4500 seconds
       Option : IA_PD (25), Length : 41
         IAID : 1
         Time1: 1800 seconds
         Time2: 2880 seconds
         Option : IAPREFIX (26), Length : 25
           Prefix : 2001:db8:d201::/64
           Preferred Lifetime : 3600 seconds
           Valid Lifetime     : 4500 seconds

DHCPv6 lease split actions are always identical for all leases in the transaction:

• DHCPv6 lease split is active for a lease when DHCPv6 relay lease split is enabled on the group interface or retail subscriber interface and when, for all IA_NA and IA_PD options in the transaction, the configured lease split valid lifetime (short lease time) is less than or equal to the following conditions:

  • the renew time T1 committed by the server (the long renew time) in the IA_NA or IA-PD Option

  • 50% of the preferred lifetime committed by the server in the IA_NA Address Option or IA_PD Prefix Option when the T1 value committed by the server equals zero

• When DHCPv6 lease split is active, the following values are updated for all IA types in the reply to the DHCPv6 client.

  • Valid lifetime (short lease time or short valid lifetime) = configured lease-split valid-lifetime

  • Preferred lifetime (short preferred lifetime) = configured lease-split valid-lifetime

  • T1 (short renew time) = 0.5 * configured lease-split valid-lifetime

  • T2 (short rebind time) = 0.8 * configured lease-split valid-lifetime

  When lease split is active, the short preferred lifetime and short valid lifetime are equal.

• Renew behavior when DHCPv6 lease split is active:

  • A client renew message is authenticated (when applicable) and relayed to the DHCP server when, for at least one of the IA options in the transaction, the next client renew message following the short renew time cycle is later than the long renew time (T1) committed by the server.

  • Otherwise, the client renew message is proxied (in other words, a renew reply is sent to the client on behalf of the server). Proxied client renew messages are not authenticated. For all IA types, the following values are included:

    • Valid lifetime (short lease time or short valid lifetime) = configured lease-split valid-lifetime

    • Preferred lifetime (short preferred lifetime) = configured lease-split valid-lifetime

    • T1 (short renew time) = 0.5 * configured lease-split valid-lifetime

    • T2 (short rebind time) = 0.8 * configured lease-split valid-lifetime

The following output shows an example of a DHCP6 relay configuration.

configure service ies service-id subscriber-interface ip-int-name group-
interface ip-int-name
--- snip ---
    ipv6
        dhcp6
            relay
                lease-split
                    valid-lifetime min 15
                    no shutdown
                exit
                server 2001:db8::1
                no shutdown
            exit
        exit
    exit

Use the following command to verify whether DHCPv6 lease split is active.

# /show service id 1000 dhcp6 lease-state detail
======================================================================
DHCP lease states for service 1000
======================================================================
--- snip ---
Remaining Lease Time : 0d 00:12:07 (Lease Split)
--- snip ---
Dhcp6 Server Addr    : 2001:db8::3
--- snip ---
Lease Info origin    : DHCP
ServerLeaseStart     : 12/15/2020 11:13:22
ServerLastRenew      : 12/15/2020 11:13:22
ServerLeaseEnd       : 12/15/2020 12:20:02