
The current configuration for the VPNinstanceNAME is as below:
ip vpn-instance VPNinstanceNAME
ipv4-family
route-distinguisher 10000:10
export route-policy rp-AS11111-policy1-exp
apply-label per-instance
vpn-target 10000:10 export-extcommunity
vpn-target 10000:10 10000:11 10000:21 import-extcommunity
ipv6-family
route-distinguisher 10000:10
apply-label per-instance
vpn-target 10000:10 export-extcommunity
vpn-target 10000:10 10000:11 10000:21 import-extcommunity
For the old IPv4 protocol, when you configure VPNv4, there is command below, to advertise the default route via VPN instance..
peer default-originate vpn-instance
Unfortunately, for the VPNv6 there is no such command at the moment and you will have to do the following workaround.
I recommend to configure static IPv6 route in the VPN instance and then configure BGP+4 to publish them to the VPNv6 peer.
ipv6 route-static vpn-instance VPNinstanceNAME :: 0 <next hop address>
#
Ipv6-family vpn-instance VPNinstanceNAME
network ::0