Specifications

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Cisco Nexus 3000 Series NX-OS Unicast Routing Configuration Guide, Release 5.0(3)U2(2)
OL-25782-02
Chapter 5 Configuring Basic BGP
Guidelines and Limitations for BGP
• You must enable the BGP feature (see the “Enabling the BGP Feature” section on page 5-11).
• You should have a valid router ID configured on the system.
• You must have an AS number, either assigned by a Regional Internet Registry (RIR) or locally
administered.
• You must configure at least one IGP that is capable of recursive next-hop resolution.
• You must configure an address family under a neighbor for the BGP session establishment.
Guidelines and Limitations for BGP
BGP has the following configuration guidelines and limitations:
• The dynamic AS number prefix peer configuration the overrides individual AS number
configuration inherited from a BGP template.
• If you configure a dynamic AS number for prefix peers in an AS confederation, BGP establishes
sessions with only the AS numbers in the local confederation.
• BGP sessions created through a dynamic AS number prefix peer ignore any configured eBGP
multihop time-to-live (TTL) value or a disabled check for directly connected peers.
• You must configure a router ID for BGP to avoid automatic router ID changes and session flaps.
• You must use the maximum-prefix configuration option per peer to restrict the number of routes
received and system resources used.
• You must configure the update-source to establish a session with BGP/eBGP multihop sessions.
• You must specify a BGP policy if you configure redistribution.
• You must define the BGP router ID within a VRF.
• If you decrease the keepalive and hold timer values, you might experience BGP session flaps.
• If you configure VRFs, enter the desired VRF (see Chapter 11, “Configuring Layer 3
Virtualization”).
CLI Configuration Modes
The following sections describe how to enter each of the CLI configuration modes for BGP. From a
mode, you can enter the ? command to display the commands available in that mode.
This section includes the following topics:
• Global Configuration Mode, page 5-9
• Address Family Configuration Mode, page 5-9
• Neighbor Configuration Mode, page 5-9
• Neighbor Address Family Configuration Mode, page 5-10