Brocade Communications Systems ICX 7250 series, Руководство по настройке

Страница: 71 / 483

2. If the administrative distances are equal:
• Are the routes from different routing protocols (RIP, OSPF, or BGP4)? If so, use the route with the lowest IP address.
• If the routes are from the same routing protocol, use the route with the best metric. The meaning of "best" metric depends
on the routing protocol:
• RIP - The metric is the number of hops (additional routers) to the destination. The best route is the route with the fewest
hops.
• OSPF - The metric is the path cost associated with the route. The path cost does not indicate the number of hops but is
instead a numeric value associated with each route. The best route is the route with the lowest path cost.
• BGP4 - The metric is the Multi-exit Discriminator (MED) associated with the route. The MED applies to routes that have
multiple paths through the same Autonomous System. The best route is the route with the lowest MED.
Example of configuring a default network route
You can configure up to four default network routes.
To configure a default network route, enter commands such as the following.
device(config)# ip default-network 10.157.22.0
device(config)# write memory
Syntax: ip default-network ip-addr
The ip-addr variable specifies the network address.
To verify that the route is in the route table, enter the following command at any level of the CLI.
device# show ip route
Total number of IP routes: 2
Start index: 1 B:BGP D:Connected R:RIP S:Static O:OSPF *:Candidate default
Destination NetMask Gateway Port Cost Type
1 10.157.20.0 255.255.255.0 0.0.0.0 lb1 1 D
2 10.157.22.0 255.255.255.0 0.0.0.0 1/4/11 1 *D
This example shows two routes. Both of the routes are directly attached, as indicated in the Type column. However, one of the routes is
shown as type "*D", with an asterisk (*). The asterisk indicates that this route is a candidate for the default network route.
Configuring IP load sharing
The IP route table can contain more than one path to a given destination. When this occurs, the Layer 3 switch selects the path with the
lowest cost as the path for forwarding traffic to the destination. If the IP route table contains more than one path to a destination and the
paths each have the lowest cost, then the Layer 3 switch uses IP load sharing to select a path to the destination.
IP load sharing uses a hashing algorithm based on the source IP address, destination IP address, and protocol field in the IP header, TCP,
and UDP information.
NOTE
IP load sharing is also called "Equal-Cost Multi-Path (ECMP) load sharing or just ECMP.
NOTE
IP load sharing is based on next-hop routing, and not on source routing.
Configuring IP parameters - Layer 3 switches
Brocade FastIron Layer 3 Routing Configuration Guide
53-1003903-04 71