It took me far to long to find out how to config this, so I'm sharing it to be more searching on the Internets.
- NXOS BGP 'upsteam' / 'north bound' peer sharing the default route only
- Linux box runs Quagga sharing it's /56 routable behind it
feature bgp router bgp 65170 router-id 188.8.131.52 address-family ipv6 unicast network 0::/0 neighbor 69::69 remote-as 65169 address-family ipv6 unicast
router bgp 65169 bgp router-id 184.108.40.206 neighbor 69::1 remote-as 65170 address-family ipv6 unicast network 2400:0000:0000:6900::/56 neighbor 69::1 activate log file /var/log/bgpd.log log stdout