Valid Route Distinguisher Formats

BD

The route distinguisher (RD) is a unique identifier used in Multiprotocol Label Switching (MPLS) VPNs to differentiate between identical routes that may exist in different VPNs. The RD is a combination of a prefix and an identifier that is assigned by the service provider to each VPN customer.

Of the options given, two formats are valid route distinguisher formats:

A. <MPLS label> : < VPN assigned number> This format uses an MPLS label and a VPN assigned number. The MPLS label is used to identify the VPN and the VPN assigned number is used to identify the particular customer or site within the VPN.

B. <autonomous system number> : < VPN assigned number> This format uses an autonomous system (AS) number and a VPN assigned number. The AS number is used to identify the VPN and the VPN assigned number is used to identify the particular customer or site within the VPN.

C. <inbound interface index> : < VPN assigned number> This format is not a valid RD format. The inbound interface index is used to identify the interface through which a particular route was learned, and is not a unique identifier for a VPN customer or site.

D. <loopback IP address> : < VPN assigned number> This format is also not a valid RD format. The loopback IP address is used as a stable address for a router's own interface, and is not a unique identifier for a VPN customer or site.

In summary, the valid RD formats are A and B, which use an MPLS label or an AS number, respectively, along with a VPN assigned number to uniquely identify a particular customer or site within a VPN.