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11-12
Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 4.x
OL-20002-02
Chapter 11 Configuring Advanced BGP
Prerequisites for BGP
Prerequisites for BGP
BGP has the following prerequisites:
• You must enable the BGP feature (see the “Enabling the BGP Feature” section on page 10-10).
• 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 have reachability (such as an interior gateway protocol (IGP), a static route, or a direct
connection) to the peer that you are trying to make a neighbor relationship with.
• You must explicitly configure an address family under a neighbor for the BGP session
establishment.
Guidelines and Limitations for BGP
BGP has the following guidelines and limitations:
• The dynamic AS number prefix peer configuration overrides the 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.
• Configure a router ID for BGP to avoid automatic router ID changes and session flaps.
• Use the maximum-prefix configuration option per peer to restrict the number of routes received and
system resources used.
• Configure the update-source to establish a session with eBGP multihop sessions.
• Specify a BGP route map if you configure redistribution.
• Configure the BGP router ID within a VRF.
• If you decrease the keepalive and hold timer values, the network might experience session flaps.
• If you configure VDCs, install the Advanced Services license and enter the desired VDC (see the
Cisco Nexus 7000 Series NX-OS Virtual Device Context Configuration Guide, Release 4.x).
• When you redistribute BGP to IGP, iBGP is redistributed as well. To override this behavior, you
must insert an additional deny statement into the route map.
Product License Requirement
Cisco NX-OS BGP requires an Enterprise Services license. For a complete explanation of the NX-OS licensing scheme
and how to obtain and apply licenses, see the Cisco NX-OS Licensing Guide
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