User's Manual

452
use soft reconfiguration, currently, we enable the soft reconfiguration based on each neighbour. When the soft
reconfiguration is used on the incoming update produced by the neighbor, it is called incoming soft
reconfiguration; When the soft reconfiguration is used on the outcoming update to the neighbor, it is called
outcoming soft reconfiguration. Applying incoming soft reconfiguration can make the new input policy effective,
Applying outcoming soft reconfiguration makes new local output policy effective without the reset of BGP
session.
In order to generate new incoming update without resetting of BGP session, local BGP speaker should save
the received incoming update without any modification, regardless whether it would be accepted or denied
under current incoming policy. This will be very memory consuming and should be avoided. On the other hand,
outcoming reconfiguration does not have any extra memory consumption, so it is always effective. You can
trigger outcoming soft reconfiguration on the other side of BGP session to make the new local incoming policy
effective.
In order to permit incoming soft reconfiguration, you should configure the BGP to save all accepted routing
update. Outcoming reconfiguration need not be pre-configured.
Use the following router configuration command to configure BGP soft reconfiguration:
Command Purpose
Neighbor
{ip-address | peer-group-name}
soft-
reconfiguration
[
inbound
]
Configure BGP soft reconfiguration
If you use parameter “peer-community-name” to designate BGP peer community, all peer community
members in it will inherit the feature of this command.
4. Reset BGP connection
Once two routers are defined as BGP neighbours, they create a BGP connection, and exchange routing
information. If the BGP routing policy has been changed, or other configurations have been changed, then you
should reset the BGP connection in order to make the change of configuration effective. Use one of the
following two management mode commands to reset BGP connection:
Command Purpose
clear ip bgp
{
*
| address} Reset all BGP connections.
Recreate a special BGP connection.
5. Configure the synchronization between BGP and IGPs
If you permit another AS to transfer data to the third AS through your AS, then the synchronization between
your AS internal routing state and the routing information it broadcasted to another ASs is very important. For
example, if your BGP wants to broadcast routes before all routers in your AS get to know the routes through
IGP, then your AS may receive some information that some routers cannot route. In order to prevent these
situations, BGP should wait until all IGP routers inside AS get to know that routing information, this is the
synchronization between BGP and IGP, and the synchronization is activated by default.
Under certain situations, it is not necessary to synchronize. If you do not permit other ASs to transfer data
through your AS, or if all routers in your AS will run BGP, your can cancel the Synchronization function.
Cancelling that feature will enable you to put fewer routes in your IGP, and enable quicker convergence of
BGP. Use the following router configuration command to cancel synchronization: