Administrator Guide

Layer 3 Routing Commands 1305
• ipv6-address [ interface interface-id] — The neighbor’s IPv6 address. If
the neighbor’s IPv6 address is a link local address, the local interface must
also be specified.
• autodetect interface interface-id — The VLAN routing interface on which
the neighbor’s link local IPv6 address is auto detected.
• local-as as-number — The AS number to advertise as the local AS in the
AS PATH sent to the neighbor.
• no-prepend — The local-as is not prepended in the AS PATH received in
the updates from this neighbor.
• replace-as — Replace the router’s own AS with the local-as in the AS
PATH sent to the neighbor.
Default Configuration
No local-as is configured for any peer.
Command Mode
BGP Router Configuration mode, IPv4 Address Family Configuration mode
User Guidelines
In typical data center deployments using CLOS networks, the peering is all
external BGP between the BGP devices requiring an unique ASN for each
router. Normally, the private BGP networks are expected to use private AS
numbers. But, there are only 1024 private AS numbers in the standard 2-byte
ASN.
Due to this limitation, data center deployments are forced to use public ASNs
in their private networks. When such private networks are interconnected to
each other, there needs to be a way to manipulate the public ASNs in the
route advertisements so that the private networks with the public ASNs don’t
experience ASN conflicts.
With the options no-prepend and replace-as
• The router replaces the global AS of the router with the configured local-as
when advertising the routes to the peer on which this command is
configured.
• As well the local-as is not prepended to the routes received from the
neighbor on which this command is configured.