300-410 · Question #78
What is a role of route distinguishers in an MPLS network?
The correct answer is D. Route distinguishers make a unique IPv4 address across the MPLS network. Route distinguishers (RDs) are crucial in an MPLS network for making IPv4 addresses globally unique across different VPNs.
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- ARoute distinguishers define which prefixes are imported and exported on the edge router
- BRoute distinguishers allow multiple instances of a routing table to coexist within the edge router.
- CRoute distinguishers are used for label bindings.
- DRoute distinguishers make a unique IPv4 address across the MPLS network
How the community answered
(43 responses)- B2% (1)
- C5% (2)
- D93% (40)
Why each option
Route distinguishers (RDs) are crucial in an MPLS network for making IPv4 addresses globally unique across different VPNs.
Route Targets (RTs) define which prefixes are imported and exported on an edge router, not Route Distinguishers.
While RDs enable multiple routing tables to coexist (within VRFs) by making routes unique, their direct role is to create the unique VPNv4 address, which is the mechanism that facilitates the coexistence of routing tables.
Label bindings are established by protocols like LDP or BGP (for VPN labels), not by Route Distinguishers, which are part of the VPNv4 address structure.
Route Distinguishers (RDs) are prepended to IPv4 prefixes to create unique VPNv4 prefixes, effectively extending the IPv4 address so that identical IPv4 addresses used in different VPNs become globally unique within the MPLS network. This uniqueness is essential for allowing overlapping IP address spaces to coexist across multiple VPNs.
Concept tested: MPLS VPNs - Route Distinguishers (RD)
Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/mp_l3_vpns/configuration/xe-16/mp-l3-vpns-xe-16-book/mp-l3-vpns-overview.html
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