Extreme Networks ExtremeWare XOS 10.1, Manual

Page: 214 / 256

214 ExtremeWare XOS 10.1 Concepts Guide
Exterior Gateway Routing Protocols
•
shortest length (shortest AS path)
• lowest origin code
• lowest MED
• route from external peer
•
lowest cost to Next Hop
• lowest routerID
Stripping Out Private AS Numbers from Route Updates
Private AS numbers are AS numbers in the range 64512 through 65534. You can remove private AS
numbers from the AS path attribute in updates that are sent to external BGP (EBGP) neighbors. Possible
reasons for using private AS numbers include:
• The remote AS does not have officially allocated AS numbers.
• You want to conserve AS numbers if you are multi-homed to the local AS.
Private AS numbers should not be advertised on the Internet. Private AS numbers can only be used
locally within an administrative domain. Therefore, when routes are advertised out to the Internet, the
routes can be stripped out from the AS paths of the advertised routes using this feature.
To configure private AS numbers to be removed from updates, use the following command:
enable bgp neighbor [<remoteaddr> | all] remove-private-AS-numbers
To disable this feature, use the following command:
disable bgp neighbor [<remoteaddr> | all] remove-private-AS-numbers
Route Re-Distribution
BGP, OSPF, and RIP can be enabled simultaneously on the switch. Route re-distribution allows the
switch to exchange routes, including static, direct, and VIP routes, between any two routing protocols.
Exporting routes from OSPF to BGP, and from BGP to OSPF, are discreet configuration functions. To run
OSPF and BGP simultaneously, you must first configure both protocols and then verify the independent
operation of each. Then you can configure the routes to export from OSPF to BGP and the routes to
export from BGP to OSPF.
Configuring Route Re-Distribution
Exporting routes between any two routing protocols are discreet configuration functions. For example,
you must configure the switch to export routes from OSPF to BGP and, if desired, you must configure
the switch to export routes from BGP to OSPF. You must first configure both protocols and then verify
the independent operation of each. Then you can configure the routes to export from OSPF to BGP and
the routes to export from BGP to OSPF.
You can use route maps to associate BGP attributes including Community, NextHop, MED, Origin, and
Local Preference with the routes. Route maps can also be used to filter out exported routes.
To enable or disable the exporting of OSPF, IS-IS, RIP, static, direct (interface), and VIP routes to BGP,
use the following commands: