A network administrator might want to rewrite (or map) one or more route targets (RTs) at an egress ASBR to different RTs
at an ingress ASBR. One use case would be to keep the RTs at the egress ASBR private from the ingress ASBR.
The rewrite is achieved by using inbound route maps, matching prefixes to route-map clauses that match inbound RTs, and mapping
those RTs to different RTs recognized by the neighbor AS. Such a rewrite configuration could be complex on inbound route maps,
with potentially hundreds of RTs that would need to be specified individually (configuring set extcommunity rt
value3 ...). If the RTs being attached to the prefixes are consecutive, the configuration can be simplified by specifying a range
of RTs. Thus, the benefits of the RT mapping range are saving time and simplifying the configuration.
Likewise, the mapping of RTs to a VPN distinguisher attribute (and vice versa) can also be simplified by specifying a range
of RTs or VPN distinguishers. The BGP—VPN Distinguisher Attribute feature allows a network administrator to keep source RTs
private from an ASBR in a destination AS. An RT at an egress ASBR is mapped to a VPN distinguisher, the VPN distinguisher
is carried through the eBGP, and then it is mapped to an RT at the ingress ASBR.
The RT and VPN Distinguisher Attribute Mapping Range feature introduces the ability to specify a range of either route targets
(RTs) or VPN distinguishers when mapping them.
Another benefit applies to setting a VPN distinguisher. Prior to this feature, only one set extcommunity vpn-distinguisher value was allowed per route-map clause. With the introduction of the mapping range, a range of VPN distinguishers can be
set on a route.