Dell Brocade DCX, Configuration Manual

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766 BigIron RX Series Configuration Guide
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Requiring the first AS to be the neighbor’s AS
26
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Unknown – 255 (the router will not use this route)
Lower administrative distances are preferred over higher distances. For example, if the router
receives routes for the same network from OSPF and from RIP, the router will prefer the OSPF route
by default. 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
route’s administrative distance is lower than other routes from different route sources to the same
destination.
•
To change the EBGP, IBGP, and Local BGP default administrative distances, see the
instructions in this section.
•
To change the default administrative distance for OSPF, RIP, ISIS, refer to “Changing
administrative distances” on page 765.
•
To change the administrative distance for static routes, refer to “Configuring static routes” on
page 191
To change the default administrative distances for EBGP, IBGP, and Local BGP, enter a command
such as the following.
BigIron RX(config-bgp)# distance 200 200 200
Syntax: 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 BGP distance and can be a value from 1 – 255.
Requiring the first AS to be the neighbor’s AS
By default, the device does not require the first AS listed in the AS_SEQUENCE field of an AS path
Update from an EBGP neighbor to be the AS that the neighbor who sent the Update is in. You can
enable the device for this requirement.
When you enable the device to require the AS that an EBGP neighbor is in to 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 ASs match. If the ASs 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.
To enable this feature, enter the following command at the BGP configuration level of the CLI.
BigIron RX(config-bgp)# enforce-first-as
Syntax: [no] enforce-first-as
Neighbor local-AS
The Neighbor Local Autonomous System (AS) allows a router that is a member of one AS to appear
to also be a member of another AS. This feature is useful, for example, if Company A purchases
Company B, but Company B does not want to modify it peering configurations.
This feature can only be used for true EBGP peers. When establishing a BGP connection, the router
will use the configured neighbor local AS, instead of the system AS number.