BGP-4 Between PE/CE Routers
Previous examples of the Carrier's Carrier architecture used LDP on the CSC PE router to CE router links to distribute labels for the IGP routes. However, in many cases, such as an ISP environment, BGP-4 is the preferred protocol for routing exchange (more so because the PE-CE protocol is usually dictated by the service providers, and many of them prefer BGP-4). Therefore, support for this protocol has been added to Cisco IOS. This support is referred to as IPv4 + Labels, or RFC 3107 support. It provides the ability to assign labels to BGP routes, which is not available in standard MPLS software, and removes the requirement of running LDP on the PE-CE links.
Figure 6-8 shows that InterCom has chosen to use BGP-4 on ...
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