What is the purpose of Route Target Constraint?
A.
to avoid using route reflectors in MPLS VPN networks
B.
to avoid using multiple route distinguishers per VPN in MPLS VPN networks
C.
to be able to implement VPLS with BGP signaling
D.
to avoid sending unnecessary BGP VPNv4 or VPNv6 updates to the PE router
E.
to avoid BGP having to perform route refreshes
With Multiprotocol Label Switching (MPLS) VPN, the internal Border Gateway Protocol (iBGP) peer or Route Reflector (RR) sends all VPN4 and/or VPN6 prefixes to the PE routers. The PE router drops the VPN4/6 prefixes for which there is no importing VPN routing and forwarding (VRF). This is a behavior where the RR sends VPN4/6 prefixes to the PE router, which it does not need. This is a waste of processing power on the RR and the PE and a waste of bandwidth.
With Route Target Constraint (RTC), the RR sends only wanted VPN4/6 prefixes to the PE. ‘Wanted’ means that the PE has VRF importing the specific prefixes.
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PE only receive update matching the RTC. where reduce many unwanted route updates.
D is correct
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