Convincing iOS devices to use ip6 autoconfigured addresses requires frequent RA messages. Roughly speaking: "ip6 nd bvi0 ra-interval 5 3 ra-lifetime 180" or similar.

When vpp renews a prefix delegation, it loses the RA frequency, lifetime parameters.

Before delegated prefix renewal:

DBGvpp# sh ip6 int bvi0
bvi0 is admin up
Local unicast address(es):
fd42:2543:e08d:25e6:b2b0:ff:fe00:0/64
Global unicast address(es):
2001:db01:0:200::2/64
Link-local address(es):
fe80::b2b0:ff:fe00:0
Joined group address(es):
ff02::1
ff02::2
ff02::16
ff02::1:ff00:0
ff02::1:ff00:2
Neighbor Discovery: enabled
ICMP redirects are disabled
ICMP unreachables are not sent
ND DAD is disabled
Advertised Prefixes:
prefix 2001:db01:0:200::, length 64
MTU is 9000
ICMP error messages are unlimited
ICMP redirects are disabled
ICMP unreachables are not sent
ND DAD is disabled
ND advertised reachable time is 0
ND advertised retransmit interval is 0 (msec)
ND router advertisements are sent every 5.0 seconds (min interval is 3.0)
ND router advertisements live for 600 seconds
Hosts don't use stateless autoconfig for addresses
ND router advertisements sent 3
ND router solicitations received 0
ND router solicitations dropped 0
VRRP VRs monitoring this link:
DBGvpp#

Delegation renewal spew:
cp_ip6_advertise_prefix:819: Advertise prefix 2001:db01:0:200::/64 valid lt 15 preferred lt 15
cp_ip6_address_add_del_now:689: Add address 2001:db01:0:200::2/64 on bvi0
cp_ip6_advertise_prefix:819: Advertise prefix 2001:db01:0:200::/64 valid lt 15 preferred lt 15
icmp6_router_solicitation:583: Prefix 2001:db01:0:200:: valid 14 preferred 14sh ip6 int bvi0

Router advertisement time parameters are gone:

DBGvpp# sh ip6 int bvi0
bvi0 is admin up
Local unicast address(es):
fd42:2543:e08d:25e6:b2b0:ff:fe00:0/64
Global unicast address(es):
2001:db01:0:200::2/64
Link-local address(es):
fe80::b2b0:ff:fe00:0
Joined group address(es):
ff02::1
ff02::2
ff02::16
ff02::1:ff00:2
Neighbor Discovery: enabled
ICMP redirects are disabled
ICMP unreachables are not sent
ND DAD is disabled
Advertised Prefixes:
prefix 2001:db01:0:200::, length 64
MTU is 9000
ICMP error messages are unlimited
ICMP redirects are disabled
ICMP unreachables are not sent
ND DAD is disabled
ND advertised reachable time is 0
ND advertised retransmit interval is 0 (msec)
ND router advertisements are sent every 200.0 seconds (min interval is 150.0)
ND router advertisements live for 600 seconds
Hosts don't use stateless autoconfig for addresses
ND router advertisements sent 1
ND router solicitations received 0
ND router solicitations dropped 0
VRRP VRs monitoring this link:

 

isc-dhcp-server configuration. Save to file, then:

isc-dhcp-server -6 -d (filename):

default-lease-time 15;
preferred-lifetime 15;
option dhcp-renewal-time 10;
option dhcp-rebinding-time 12;
subnet6 2001:db01:0:1::/64

{ range6 2001:db01:0:1::1 2001:db01:0:1::9; prefix6 2001:db01:0:100:: 2001:db01:0:200::/56; } Configure an interface on the same network segment as vpp/eth1, or the dhcp6 server will refuse to start. ifconfig eth1 inet6 add 2001:db01:0:1::10/64   VPP config:  set term pag off comment \{ "internet" }

create host-interface name eth1
set int ip address host-eth1 10.26.68.100/24
set int ip6 table host-eth1 0
set int state host-eth1 up

ip6 nd address autoconfig host-eth1 default-route
dhcp6 client host-eth1
dhcp6 pd client host-eth1 prefix group hgw
set ip6 address bvi0 prefix group hgw ::2/64
ip6 nd address autoconfig bvi0 default-route
ip6 nd bvi0 ra-interval 5 3 ra-lifetime 180