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Cisco Catalyst Blade Switch 3130 and 3032 for Dell Software Configuration Guide
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Chapter 38 Configuring IP Unicast Routing
Configuring BGP
3.
Prefer the route with the highest local preference. Local preference is part of the routing update and
is exchanged among routers in the same autonomous system. The default value of the local
preference attribute is 100. You can set local preference by using the
bgp default local-preference
router configuration command or by using a route map.
4.
Prefer the route that was originated by BGP running on the local router.
5.
Prefer the route with the shortest autonomous-system path.
6.
Prefer the route with the lowest origin type. An interior route or IGP is lower than a route learned
by
EGP, and an EGP-learned route is lower than one of unknown origin or learned in another way.
7.
Prefer the route with the lowest multi-exit discriminator (MED) metric attribute if the neighboring
autonomous system is the same for all routes considered. You can configure the MED by using route
maps or by using the
default-metric
router configuration command. When an update is sent to an
IBGP peer, the MED is included.
8.
Prefer the external (EBGP) path over the internal (IBGP) path.
9.
Prefer the route that can be reached through the closest IGP neighbor (the lowest IGP metric). This
means that the router prefers the shortest internal path within the autonomous system to reach the
destination (the shortest path to the BGP next hop).
10.
If these conditions are all true, insert the route for this path into the IP routing table:
•
Both the best route and this route are external.
•
Both the best route and this route are from the same neighboring autonomous system.
•
maximum-paths is enabled.
11.
If multipath is not enabled, prefer the route with the lowest IP address value for the BGP router ID.
The router ID is usually the highest IP address on the router or the loopback (virtual) address, but
might be implementation-specific.
Beginning in privileged EXEC mode, follow these steps to configure some decision attributes:
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
router bgp
autonomous-system
Enable a BGP routing process, assign it an
autonomous-system number, and enter router
configuration mode.
Step 3
bgp best-path as-path ignore
(Optional) Configure the router to ignore
autonomous-system path length in selecting a route.
Step 4
neighbor
{
ip-address
|
peer-group-name
}
next-hop-self
(Optional) Disable next-hop processing on BGP updates
to a neighbor by entering a specific IP address to be used
instead of the next-hop address.
Step 5
neighbor
{
ip-address
|
peer-group-name
}
weight
weight
(Optional) Assign a weight to a neighbor connection.
Values are from 0 to 65535; the largest weight is the
preferred route. Routes learned through another BGP peer
have a default weight of 0; routes sourced by the local
router have a default weight of 32768.
Step 6
default-metric
number
(Optional) Set a MED metric to set preferred paths to
external neighbors. All routes without a MED are also set
to this value. The range is 1 to 4294967295. The lowest
value is the most desirable.
