We recently enabled IPv6 across our backbone. The following is an example configuration for a 7600 router running the SUP 720. All operations listed here resulted in zero downtime or impact to the existing IPv4 customers and IPv4 BGP peers.

ipv6 unicast-routing
interface Loopback0
ipv6 address xxxx:yyyy::1/128
ipv6 enable
!
interface GigabitEthernet2/2
ipv6 address aaaa:bbbb:0:2::FFE2/126
ipv6 enable
ipv6 nd suppress-ra
!
router bgp 65534
no bgp default ipv4-unicast
neighbor ipv6peer peer-group
neighbor ipv6peer description IPv6 Peer Group
neighbor ipv6peer version 4
neighbor cccc:dddd::1 remote-as 65535
neighbor cccc:dddd::1 peer-group ipv6peer
address-family ipv6
network xxxx:yyyy::0/32
neighbor ipv6peer activate
neighbor ipv6peer next-hop-self
neighbor ipv6peer send-community
neighbor ipv6peer remove-private-as
neighbor ipv6peer soft-reconfiguration inbound
neighbor aaaa:bbbb:0:2::FFE1 peer-group ipv6peer
neighbor aaaa:bbbb:0:2::FFE1 activate
exit
!
ipv6 route xxxx:yyyy::0/32 Null0 254