Foundry Networks FESX User Manual

Foundry Configuration Guide for the FESX, FSX, and FWSX
21 - 30 © Foundry Networks, Inc. December 2005
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 Layer 3 Switch 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, see “Modify Administrative Distance” on page 20-32.
• To change the default administrative distance for RIP, see “Changing the Administrative Distance” on
page 17-5.
• To change the default administrative distance for static routes, see “Configuring Static Routes” on page 16-
32.
You can change the default EBGP, IBGP, and Local BGP administrative distances using either of the following
methods.
To change the default administrative distances for EBGP, IBGP, and Local BGP, enter a command such as the
following:
FESX424 Router(config-bgp-router)# distance 180 160 40
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 Foundry 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
Foundry device for this requirement.
When you enable the Foundry 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 Foundry device accepts the Update only if the
ASs match. If the ASs do not match, the Foundry 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:
FESX424 Router(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:
FESX424 Router(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 21-4 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.

Foundry Networks FESX Specifications

General

Brand	Foundry Networks
Model	FESX
Category	Switch
Language	English