In our ISP network, all our PE routers are configured BGP with two RR with MPLS enabled and OSPF as backbone IGP.
My query is, when i am configuring new link on MPLS BGP means client end router running on BGP alone, when i am enabling bgp sunchronization at CE router, still CE router getting all BGP routes into the routing table, why is this happening?
service provider signalling plane uses OSPF as IGP, LDP for label exchange, BGP in multiprotocol version.
A CE peers in eBGP with a PE and you define the CE neighbor ip address in address-family ipv4 vrf .
So, BGP synchronization cannot apply on the PE side because VRF routes are not present in the Global routing table and they will never be.
BGP synchronization could apply to an eBGP neighbor defined in address-family ipv4 unicast that is the Global Routing Table.
Also if you enable BGP synchronization at CE router this influences how and if CE router advertises BGP prefixes to PE router and not what PE node advertises to CE node.
the CE router should wait to advertise BGP prefixes received on an iBGP session to see the same prefixes learned in an IGP.
Again if the CE is the only node in the site and advertises only connected routes it should be able to advertise them even with BGP sync. enabled.
Hope to help