Reference Guide

204 | Border Gateway Protocol IPv4 (BGPv4)
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Use the following command in the CONFIGURATION ROUTER BGP mode to allow multiple paths sent
to peers.
Configure IP community lists
Within FTOS, you have multiple methods of manipulating routing attributes. One attribute you can
manipulate is the COMMUNITY attribute. This attribute is an optional attribute that is defined for a group
of destinations. In FTOS, you can assign a COMMUNITY attribute to BGP routers by using an IP
Community list. After you create an IP Community list, you can apply routing decisions to all routers
meeting the criteria in the IP Community list.
IETF RFC 1997 defines the COMMUNITY attribute and the pre-defined communities of INTERNET,
NO_EXPORT_SUBCONFED, NO_ADVERTISE, and NO_EXPORT. All BGP routes belong to the
INTERNET community. In the RFC, the other communities are defined as follows:
• All routes with the NO_EXPORT_SUBCONFED (0xFFFFFF03) community attribute are not sent to
CONFED-EBGP or EBGP peers, but are sent to IBGP peers within CONFED-SUB-AS
• All routes with the NO_ADVERTISE (0xFFFFFF02) community attribute must not be advertised
• All routes with the NO_EXPORT (0xFFFFFF01) community attribute must not be advertised outside a
BGP confederation boundary, but are sent to CONFED-EBGP and IBGP peers
FTOS also supports BGP Extended Communities as described in RFC 4360—BGP Extended
Communities Attribute.
Note: In some cases, while receiving 1K same routes from more than 64 iBGP neighbors, BGP sessions
holdtime of 10 seconds may flap. The BGP add-path does not update packets for advertisement and
cannot scale to higher numbers. Either reduce the number of routes added or increase the holddown
timer value.
Step Command Syntax Command Mode Purpose
1
bgp add-path [send |
receive | both]
count
CONFIG-ROUTER-BGP Allow the advertisement of multiple paths for the
same address prefix without the new paths
replacing any previous ones.
Range: 2-64
2
neighbor add-path
CONFIG-ROUTER-BGP Allow the specified neighbor/peer group to send/
receive multiple path advertisements.
3
max-path number
CONFIG-ROUTER-BGP Configure the maximum number of parallel
routes (multipath support) BGP supports. Range:
2-64