Last Updated on August 6, 2021 by Admin 3
Which of the following is appended to a VPNv4 BGP route to indicate membership in an RFC 4364 MPLS VPN? (Select the best answer.)
- a label
- an RT
- an RD
- an LSP
- a VRF
A route target (RT) is appended to a virtual private network version 4 (VPNv4) Border
Gateway Protocol (BGP) route to indicate membership in a Request for Comments (RFC)4364 Multiprotocol Label Switching (MPLS) VPN. Export RTs associate each route with one or more VPNs, and import RTs are associated with each VPN routing and forwarding (VRF) table to determine the routes that should be imported into the VRF; a VRF is a routing table instance for a VPN. A label is assigned to each VPNv4 address prefix, and the inboundtooutbound label mapping is stored in the Label Forwarding Information Base (LFIB). By configuring import and export RTs, you can configure which sites can reach each other. For example, you can configure RTs so that CustomerA and CustomerB can communicate with ProviderZ, but CustomerA and CustomerB cannot communicate with one another.
To configure RTs, you should issue the routetarget {import | export | both} valuecommand. The import, export, and both keywords specify whether extended community attributes should be imported, exported, or both. The value parameter should use one of the following formats:
– AS:nn, where AS is a 16bit autonomous system number (ASN) and nn is a 32bit decimal number
– A.B.C.D:nn, where A.B.C.D is a 32bit IP address and nn is a 16bit decimal number
A route distinguisher (RD) is a value that is added to the beginning of an IP address to create a globally unique VPNv4 address. RDs enable customers to use the same or overlapping IP address ranges on their internal networks. To create an RD, you should issue the rd value command, where the value parameter uses the same formats as the value parameter in the route-target command.
There are three types of RDs: Type 0, Type 1, and Type 2. The type of RD configuration you create depends on how you issue the value parameter of the rd command and whether you are configuring a multicast VPN environment. Type 0 and Type 1 RDs are used in unicast configurations. A Type 0 RD is configured by issuing the value parameter of the rd command with the 16bit ASN in front of the 32bit decimal number. A Type 1 RD is configured by issuing the value parameter of the rd command with the 32bit decimal number in front of the 16bit ASN. A Type 2 RD is configured similarly to a Type 1 RD but only applies to multicast VPN configurations.
A label switched path (LSP) is the path that labeled packets take through an MPLS network from one label switch router (LSR) to another. The 32bit MPLS label is used by LSRs to make forwarding decisions along the LSP. The MPLS label is placed between the Layer 2 header and the Layer 3 header. The structure of an MPLS label is shown below:
