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16-32 Riverstone Networks RS Switch Router User Guide Release 8.0
BGP Configuration Examples BGP Configuration Guide
Note the following when using the
set-pref
option:
•
All routers in the same network that are running ROSRD and participating in IBGP should use the
set-pref
option, and the
set-pref
metric should be set to the same value.
For example, in Figure 16-7, routers R12, R13, and R14 have the following line in their CLI configuration files:
•
The value of the
set-pref
option should be consistent with the import policy in the network.
The metric value should be set high enough to avoid conflicts between BGP routes and IGP or static routes. For
example, if the import policy sets ROSRD preferences ranging from 170 to 200, a set-pref metric of 170 would
make sense. You should set the metric high enough to avoid conflicts between BGP routes and IGP or static routes.
16.3.6 Multi-Exit Discriminator Attribute Example
Multi-Exit Discriminator (MED) is a BGP attribute that affects the route selection process. MED is used on external
links to discriminate among multiple exit or entry points to the same neighboring AS. All other factors being equal,
the exit or entry point with a lower metric should be preferred. If received over external links, the MED attribute may
be propagated over internal links to other BGP speakers within the same AS. The MED attribute is never propagated
to other BGP speakers in neighboring autonomous systems.
Figure 16-8 shows a sample BGP configuration where the MED attribute has been used.
Figure 16-8 Sample BGP configuration (MED attribute)
bgp set peer-group as901 set-pref 100
Physical Link
Legend:
Peering Relationship
Information Flow
C1
AS 64752
N1
10.200.12.15/24
10.200.12.4/24
10.200.12.0/24
10.200.12.6/24
AS 64751
172.16.200.4/24
172.16.200.6/24
R
4
R
6