Brocade Communications Systems FastIron SX 1600, Configuration Manual, Page: 73 / 593

• Exterior Border Gateway Protocol (EBGP) - 20
• OSPF - 110
• Interior Gateway Protocol (IBGP) - 200
• Local BGP - 200
• Unknown - 255 (the router will not use this route)
Lower administrative distances are preferred over higher distances. For example, if the router receives routes for the same network from
OSPF and from IBGP, the router will prefer the OSPF route by default.
NOTE
You can change the administrative distances individually. Refer to the configuration chapter for the route source for
information.
Since the software selects only the path with the lowest administrative distance, and the administrative distance is determined by the path
source. IP load sharing applies only when the IP route table contains multiple paths to the same destination, from the same IP route
source.
IP load sharing does not apply to paths that come from different sources.
Path cost
The cost parameter provides a common basis of comparison for selecting from among multiple paths to a given destination. Each path
in the IP route table has a cost. When the IP route table contains multiple paths to a destination, the Layer 3 switch chooses the path with
the lowest cost. When the IP route table contains more than one path with the lowest cost to a destination, the Layer 3 switch uses IP
load sharing to select one of the lowest-cost paths.
The source of a path cost value depends on the source of the path:
• IP static route - The value you assign to the metric parameter when you configure the route. The default metric is 1.
• OSPF - The Path Cost associated with the path. The paths can come from any combination of inter-area, intra-area, and
external Link State Advertisements (LSAs).
• BGP4 - The path Multi-Exit Discriminator (MED) value.
NOTE
If the path is redistributed between two or more of the above sources before entering the IP route table, the cost can increase
during the redistribution due to settings in redistribution filters.
Static route, OSPF, and BGP4 load sharing
IP load sharing and load sharing for BGP4 routes are individually configured. Multiple equal-cost paths for a destination can enter the IP
route table only if the source of the paths is configured to support multiple equal-cost paths. For example, if BGP4 allows only one path
with a given cost for a given destination, the BGP4 route table cannot contain equal-cost paths to the destination. Consequently, the IP
route table will not receive multiple equal-cost paths from BGP4.
The load sharing state for all the route sources is based on the state of IP load sharing. Since IP load sharing is enabled by default on all
Brocade Layer 3 switches, load sharing for static IP routes, OSPF routes, and BGP4 routes also is enabled by default.
Configuring IP parameters - Layer 3 switches
FastIron Ethernet Switch Layer 3 Routing
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