Information Technology Reference
In-Depth Information
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Max-free setting
—The Max-free setting should be more than the permanent buffers
plus the Min-free value. This helps prevent buffers from being trimmed prematurely.
The configuration commands for small-buffer tuning are shown in Example 3-3.
Buffer Tuning Configuration
Example 3-3
buffer small permanent 1000
buffer small min-free 250
buffer small max-free 1375
Buffer tuning should be done with care. The buffer tuning performed here is specific to
route reflectors that are subject to massive influxes of TCP ACKs. If a large number of TCP
retransmissions are seen on the BGP sessions with significant buffer failures, buffer tuning
is a possible option. When performing buffer tuning, it is best to involve the Cisco Technical
Assistance Center (TAC).
BGP Update Generation
The focus of this chapter so far has been on reducing the bottlenecks in the transport of BGP
updates. The first section focused on optimizing the TCP aspects of the transport, and the
second section focused on ensuring that the router can handle the amount of traffic deliv-
ered. The most significant performance gains in achieving fast BGP convergence are found
in the manner in which updates are generated.
The bottlenecks in the default TCP and queue configurations are not a significant factor if
the router is unable to generate BGP update messages efficiently. This section focuses on
the following methods of improving update generation, which are the basis for any BGP
convergence tuning:
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Peer groups
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BGP dynamic update peer groups
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Update packing enhancement
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BGP read-only mode
Peer Groups
Peer groups provide the foundation for optimizing BGP convergence. Peer groups provide
a mechanism for BGP peers that have the same outbound policy to be associated with each
other. This feature has two major benefits: configuration reduction and the ability to
replicate updates between peers.
The most common reason for deploying peer groups is configuration reduction. The peer
group is formed, and the common outbound policy is applied to the peer group. Each peer that
