When VPP responds to Router Solicitation request with a Router Advertisement packet, the packet's destination IPv6 address should be the same as the source address of the solicitation request.

Currently VPP uses the All Nodes Multicast as a destination address for both solicited and unsolicited Router Advertisement.

Here's the packet I sent:
###[ Ethernet ]###
dst = 33:33:00:00:00:02
src = 08:00:27:60:26:ab
type = 0x86dd
###[ IPv6 ]###
version = 6L
tc = 0L
fl = 0L
plen = 8
nh = ICMPv6
hlim = 255
src = fe80::a00:27ff:fe60:26ab
dst = ff02::2
###[ ICMPv6 Neighbor Discovery - Router Solicitation ]###
type = Router Solicitation
code = 0
cksum = 0x262c
res = 0

And the response:
###[ Ethernet ]###
dst = 08:00:27:60:26:ab
src = 08:00:27:b2:cc:05
type = 0x86dd
###[ IPv6 ]###
version = 6L
tc = 0L
fl = 0L
plen = 32
nh = ICMPv6
hlim = 255
src = fe80::a00:27ff:feb2:cc05
dst = ff02::1
###[ ICMPv6 Neighbor Discovery - Router Advertisement ]###
type = Router Advertisement
code = 0
cksum = 0x1764
chlim = 64
M = 0L
O = 0L
H = 0L
prf = Medium (default)
P = 0L
res = 0L
routerlifetime= 600
reachabletime= 0
retranstimer= 0
###[ ICMPv6 Neighbor Discovery Option - Source Link-Layer Address ]###
type = 1
len = 1
lladdr = 08:00:27:b2:cc:05
###[ ICMPv6 Neighbor Discovery Option - MTU ]###
type = 5
len = 1
res = 0x0
mtu = 9202