Route Reflection And Redundancy; Route Reflection And Looping; Figure 44: Route Reflection: Logical Redundancy; Figure 45: Route Reflection: Physical And Logical Redundancy - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - BGP AND MPLS CONFIGURATION GUIDE 2010-10-12 Configuration Manual

JunosE 11.3.x BGP and MPLS Configuration Guide
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Route Reflection and Redundancy

Reliability and redundancy are important issues when using route reflection because the
members of a cluster are not fully meshed. For example, if router Harvard in Figure 43
on page 145 goes down, all of its clients are isolated from networks outside the cluster.
Having one or more redundant route reflectors in a cluster protects against such an
occurrence.
However, you cannot rely on logical redundancy alone. Consider the cluster shown in
Figure 44 on page 146. The operator has attempted to provide redundancy in Cluster 9
by configuring two route reflectors, router Acton and router Westford. Unfortunately,
router Harvard is physically isolated if its link to router Acton goes down, or if router Acton
itself goes down. Similarly, router Plymouth is isolated if any problems develop with
router Westford.

Figure 44: Route Reflection: Logical Redundancy

In Figure 45 on page 146, the operator has added physical redundancy to the cluster
configuration. Now, loss of either one of the route reflectors does not isolate the reflector
clients.

Figure 45: Route Reflection: Physical and Logical Redundancy

Route Reflection and Looping

BGP prevents looping between ASs by evaluating the AS-path attribute to determine a
route's origin. Border routers reject routes they receive from external neighbors if the AS
path indicates that the route originated within the border router's AS.
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