Brocade Communications Systems Layer 3 Routing Configuration ICX 6650 - Manual (Page 333)

Brocade ICX 6650 Layer 3 Routing Configuration Guide 315
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Optional BGP4 configuration tasks
Requiring the first AS to be the neighbor AS
By default, the Brocade 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 Brocade device for this requirement.
When you enable the Brocade 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 Brocade device
accepts the Update only if the autonomous systems match. If the autonomous systems do not
match, the Brocade 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.
Brocade(config-bgp-router)#enforce-first-as
Syntax: [no] enforce-first-as
Disabling or re-enabling comparison of the
AS-Path length
AS-Path comparison is Step 5 in the algorithm BGP4 uses to select the next path for a route.
Comparison of the AS-Path length is enabled by default. To disable it, enter the following command
at the BGP configuration level of the CLI.
Brocade(config-bgp-router)#as-path-ignore
This command disables comparison of the AS-Path lengths of otherwise equal paths. When you
disable AS-Path length comparison, the BGP4 algorithm shown in
“How BGP4 selects a path for a
route” on page 283 skips from Step 4 to Step 6.
Syntax: [no] as-path-ignore
Enabling or disabling comparison of the router IDs
Router ID comparison is Step 10 in the algorithm BGP4 uses to select the next path for a route.
NOTE
Comparison of router IDs is applicable only when BGP4 load sharing is disabled.
When router ID comparison is enabled, the path comparison algorithm compares the router IDs of
the neighbors that sent the otherwise equal paths:
• If BGP4 load sharing is disabled (maximum-paths 1), the Layer 3 switch selects the path that
came from the neighbor with the lower router ID.
• If BGP4 load sharing is enabled, the Layer 3 switch load shares among the remaining paths. In
this case, the router ID is not used to select a path.
NOTE
Router ID comparison is disabled by default. In previous releases, router ID comparison is enabled
by default and cannot be disabled.
To enable router ID comparison, enter the compare-routerid command at the BGP configuration
level of the CLI.