Requiring The First As To Be The Neighbor's As; Neighbor Local-As; Enabling Fast External Fallover - Dell PowerConnect B-RX Configuration Manual

26

Requiring the first AS to be the neighbor's AS

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 BigIron RX 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 its 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.
For example, if you want a router to use AS 200, instead of 100 when peering with neighbor
11.11.11.2, enter commands such as the following.
BigIron RX(config)#router bgp
BigIron RX(config-bgp-router)#local-as 100
BigIron RX(config-bgp-router)#graceful-restart restart-time 30
BigIron RX(config-bgp-router)#graceful-restart
BigIron RX(config-bgp-router)#neighbor 11.11.11.2 remote-as 101
BigIron RX(config-bgp-router)#neighbor 11.11.11.2 local-as 200
Syntax: [no] neighbor <ip-address> local-as <local-as-number>
Enter the IP address of the neighbor with which the device will be peering for <ip-address>.

Enabling fast external fallover

BGP4 routers rely on KEEPALIVE and UPDATE messages from neighbors to signify that the
neighbors are alive. For BGP4 neighbors that are two or more hops away, such messages are the
only indication that the BGP4 protocol has concerning the alive state of the neighbors. As a result,
if a neighbor dies, the router will wait until the Hold Time expires or the TCP connection fails before
concluding that the neighbor is dead and closing its BGP4 session and TCP connection with the
neighbor.
758 BigIron RX Series Configuration Guide
53-1001986-01