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of the interface directly connected to the router. First, the BGP process determines if all internal BGP
peers are reachable, then it determines which peers outside the AS are reachable.
NOTE: Sample Configurations for enabling BGP routers are found at the end of this chapter.
1. Assign an AS number and enter ROUTER BGP mode.
CONFIGURATION mode
router bgp as-number
• as-number: from 0 to 65535 (2 Byte) or from 1 to 4294967295 (4 Byte) or 0.1 to 65535.65535
(Dotted format).
Only one AS is supported per system.
NOTE: If you enter a 4-Byte AS number, 4-Byte AS support is enabled automatically.
a. Enable 4-Byte support for the BGP process.
NOTE: This command is OPTIONAL. Enable if you want to use 4-Byte AS numbers or if you
support AS4 number representation.
CONFIG-ROUTER-BGP mode
bgp four-octet-as-support
NOTE: Use it only if you support 4-Byte AS numbers or if you support AS4 number
representation. If you are supporting 4-Byte ASNs, enable this command.
Disable 4-Byte support and return to the default 2-Byte format by using the no bgp four-
octet-as-support command. You cannot disable 4-Byte support if you currently have a 4-
Byte ASN configured.
Disabling 4-Byte AS numbers also disables ASDOT and ASDOT+ number representation. All AS
numbers are displayed in ASPLAIN format.
b. Enable IPv4 multicast or IPv6 mode.
CONFIG-ROUTER-BGP mode
address-family [ipv4 | ipv6} vrf
Use this command to enter BGP for IPv6 mode (CONF-ROUTER_BGPv6_AF).
2. Add a neighbor as a remote AS.
CONFIG-ROUTER-BGP mode
neighbor {ip-address | peer-group name} remote-as as-number
• peer-group name: 16 characters
• as-number: from 0 to 65535 (2 Byte) or from 1 to 4294967295 (4 Byte) or 0.1 to 65535.65535
(Dotted format)
Formats: IP Address A.B.C.D
You must Configure Peer Groups before assigning it a remote AS.
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Border Gateway Protocol IPv4 (BGPv4)