Brocade Communications Systems Layer 3 Routing Configuration ICX 6650 - Manual (Page 73)

Brocade ICX 6650 Layer 3 Routing Configuration Guide 55
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Configuring IP parameters – Layer 3 Switches
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 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.
1
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 based on next-hop routing, and not on source routing.
NOTE
The term “path” refers to the next-hop router to a destination, not to the entire route to a destination.
Thus, when the software compares multiple equal-cost paths, the software is comparing paths that
use different next-hop routers, with equal costs, to the same destination.
In many contexts, the terms “route” and ”path” mean the same thing. Most of the user
documentation uses the term “route” throughout. The term “path” is used in this section to refer to
an individual next-hop router to a destination, while the term “route” refers collectively to the
multiple paths to the destination. Load sharing applies when the IP route table contains multiple,
equal-cost paths to a destination.
NOTE
Brocade devices also perform load sharing among the ports in aggregate links. Refer to the section
“Trunk group load sharing” in the Brocade ICX 6650 Platform and Layer 2 Switching Configuration
Guide.
How multiple equal-cost paths enter the IP route table
IP load sharing applies to equal-cost paths in the IP route table. Routes that are eligible for load
sharing can enter the table from any of the following sources:
• IP static routes
• Routes learned through RIP
• Routes learned through OSPF
1. IP load sharing is also called “Equal-Cost Multi-Path (ECMP)” load sharing or just “ECMP”
Brocade# 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 1/1/1 1 *D