Information Technology Reference
In-Depth Information
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The optimization of the queuing system on the router is performed to handle the
additional load generated by the update replication.
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The TCP MSS manipulation with Path MTU Discovery is done to maximize the size
of the BGP updates, reducing the number of BGP update messages and corresponding
TCP ACKs.
•
The read-only mode and update packing efficiencies maximize the effectiveness of
each BGP update.
These features all enhance BGP's behavior independently; however, maximum impact is
gained through the interdependency of the enhancements themselves.
BGP Network Performance Features
The topic of BGP performance is not solely about optimizing the BGP update process.
Converging BGP on the network from a cold start is a very important aspect; however, the
handling of network-affecting events is also an important topic. This section focuses on
mitigating the impact of network failures and prefix update optimizations.
Network Failure Impact Mitigation
The failure of a node or link in the network is inevitable. Detecting the failure quickly and
minimizing its impact is important for maintaining high network availability. In addition to
handling failures quickly, the interaction between IGP and BGP can result in problematic
recovery scenarios. This section covers the following features of failure mitigation:
•
BGP fast external fallover
—The BGP fast external fallover feature provides a
mechanism for BGP to quickly tear down an eBGP session without waiting for the
hold timer to expire.
•
IGP/BGP convergence time deltas
—The rate at which the IGP and BGP converges
can create situations in which traffic loss is incurred. Mechanisms available in both
IS-IS and OSPF help mitigate this issue.
•
BGP Non-Stop Forwarding (NSF)
—This feature is also called
graceful restart
. It is
designed to make the restart of the BGP process invisible to the rest of the network.
BGP Fast External Fallover
The default behavior for tearing down a BGP session is to require the hold timer to expire,
which by default is 180 seconds. The BGP fast external fallover function triggers the
teardown of an eBGP session immediately when the link to that eBGP peer fails.
