Administrator Guide

ROUTER-BGP Mode
shutdown address-family-ipv6-unicast
When you configure BGP, you must explicitly enable the BGP neighbors using the following commands:
neighbor {ip-address | peer-group name} remote-as as-number
neighbor {ip-address | peer-group-name} no shutdown
For more information on enabling BGP, see Enabling BGP.
When you use the shutdown all command in global configuration mode, this command takes precedence over the shutdown
address-family-ipv4-unicast, shutdown address-family-ipv4-multicast, and shutdown address-family-
ipv6-unicast commands. Irrespective of whether the BGP neighbors are disabled earlier, the shutdown all command brings down
all the configured BGP neighbors.
When you issue the no shutdown all command, all the BGP neighbor neighbors are enabled. However, when you re-enable all the
BGP neighbors in global configuration mode, only the neighbors that were not in disabled state before the global shutdown come up.
Meaning, BGP neighbors corresponding to the IPv4 unicast or multicast address family and the IPv6 unicast address family that were
explicitly disabled before the global shutdown remains in disabled state. Use the no shutdown address-family-ipv4-unicast,
no shutdown address-family-ipv4-multicast, or no shutdown address-family-ipv6-unicast commands to
enable these neighbors.
NOTE: This behavior applies to all BGP neighbors. Meaning, BGP neighbors that were explicitly disabled before global
shutdown also remain in disabled state. Enable these neighbors individually using the no shutdown command.
Route Map Continue
The BGP route map continue feature, continue [sequence-number], (in ROUTE-MAP mode) allows movement from one route-
map entry to a specific route-map entry (the sequence number).
If you do not specify a sequence number, the continue feature moves to the next sequence number (also known as an “implied continue”).
If a match clause exists, the continue feature executes only after a successful match occurs. If there are no successful matches, continue
is ignored.
Match a Clause with a Continue Clause
The continue feature can exist without a match clause.
Without a match clause, the continue clause executes and jumps to the specified route-map entry. With a match clause and a continue
clause, the match clause executes first and the continue clause next in a specified route map entry. The continue clause launches only
after a successful match. The behavior is:
• A successful match with a continue clause—the route map executes the set clauses and then goes to the specified route map entry
after execution of the continue clause.
• If the next route map entry contains a continue clause, the route map executes the continue clause if a successful match occurs.
• If the next route map entry does not contain a continue clause, the route map evaluates normally. If a match does not occur, the route
map does not continue and falls-through to the next sequence number, if one exists
Set a Clause with a Continue Clause
If the route-map entry contains sets with the continue clause, the set actions operation is performed first followed by the continue clause
jump to the specified route map entry.
• If a set actions operation occurs in the first route map entry and then the same set action occurs with a different value in a
subsequent route map entry, the last set of actions overrides the previous set of actions with the same set command.
• If the set community additive and set as-path prepend commands are configured, the communities and AS numbers
are prepended.
Configuring BGP Confederations
Another way to organize routers within an AS and reduce the mesh for IBGP peers is to configure BGP confederations.
As with route reflectors, BGP confederations are recommended only for IBGP peering involving many IBGP peering sessions per router.
Basically, when you configure BGP confederations, you break the AS into smaller sub-AS, and to those outside your network, the
Border Gateway Protocol (BGP)
205