Network Router User Manual

SmartSwitch Router User Reference Manual 155
Chapter 12: BGP Configuration Guide
For example, in Figure 14, routers SSR12, SSR13, and SSR14 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 GateD 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.
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 15 shows a sample BGP configuration where the MED attribute has been used.
Figure 15. 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
SSR4
SSR6