Requiring the first as to be the neighbor as – Brocade Virtual ADX Switch and Router Guide (Supporting ADX v03.1.00) User Manual
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Brocade Virtual ADX Switch and Router Guide
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Requiring the first AS to be the neighbor AS
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When selecting a route from among different sources (BGP4, OSPF, static routes, and so on), the
software compares the routes on the basis of the administrative distance for each route. If the
administrative distance of the paths is lower than the administrative distance of paths from other
sources (such as static IP routes or OSPF), the BGP4 paths are installed in the IP route table.
The default administrative distances on the device are:
•
Directly connected – 0 (this value is not configurable)
•
Static – 1 is the default and applies to all static routes, including default routes. This can be
assigned a different value.
•
EBGP – 20
•
OSPF – 110
•
IBGP – 200
•
Local BGP4 – 200
•
Unknown – 255 (the device will not use this route)
Lower administrative distances are preferred over higher distances. The administrative distances
are configured in different places in the software. The device re-advertises a learned best BGP4
route to neighbors by default, regardless of whether the administrative distance for the route is
lower than the administrative distances of other routes from different route sources to the same
destination:
•
To change the EBGP, IBGP, and Local BGP4 default administrative distances, refer to the
instructions in this section.
•
To change the default administrative distance, refer to
“Changing administrative distances”
•
To change the administrative distance for static routes, refer to
“Configuring a static IP route”
To change the default administrative distances for EBGP, IBGP, and Local BGP4, enter a command
such as the following.
Virtual ADX(config-bgp)# distance 200 200 200
Syntax: [no] distance external-distance internal-distance local-distance
The external-distance sets the EBGP distance and can be a value from 1 – 255.
The internal-distance sets the IBGP distance and can be a value from 1 – 255.
The local-distance sets the Local BGP4 distance and can be a value from 1 – 255.
Requiring the first AS to be the neighbor AS
By default, a device does not require the first AS listed in the AS_SEQUENCE field of an AS path
update message from EBGP neighbors to be the AS of the neighbor that sent the update. However,
you can enable the device to have this requirement. You can enable this requirement globally for
the device, or for a specific neighbor. This section describes how to enable this requirement.
When you configure the device to require that the AS an EBGP neighbor is in be the same as the
first AS in the AS_SEQUENCE field of an update from the neighbor, the device accepts the update
only if the AS numbers match. If the AS numbers do not match, the device sends a notification
message to the neighbor and closes the session. The requirement applies to all updates received
from EBGP neighbors.