Load Balancing - Cisco 6000 Series Configuration Manual

Load Balancing

Load Balancing
Load balancing is a forwarding mechanism which distributes traffic over multiple links, based on Layer 3
routing information in the router. Per-flow load balancing is supported on all links in the bundle. This scheme
achieves load sharing by allowing the router to distribute packets over one of the links in the bundle, that is
determined through a hash calculation. The hash calculation is an algorithm for link selection based on certain
parameters.
The standard hash calculation is a 3-tuple hashing, using the following parameters:
• IP source address
• IP destination address
• Router ID
7-tuple hashing can also be configured. based on Layer 3 and Layer 4 parameters:
• IP source address
• IP destination address
• Router ID
• Input interface
• IP protocol
• Layer 4 source port
• Layer 4 destination port
When per-flow load balancing and 3-tuple hashing is enabled, all packets for a certain source-destination pair
will go through the same link, though there are multiple links available. Per-flow load balancing ensures that
packets for a certain source-destination pair arrive in order.
Note
For multicast traffic, ingress forwarding is based on the Fabric Multicast Group Identifier (FGID). Egress
forwarding over the bundle is based on the bundle load balancing.
VLANs on an Ethernet Link Bundle
802.1Q VLAN subinterfaces can be configured on 802.3ad Ethernet link bundles. Keep the following
information in mind when adding VLANs on an Ethernet link bundle:
• The maximum number of VLANs allowed per bundle is 128.
• The maximum number of bundled VLANs allowed per router is 4000.
Note The memory requirement for bundle VLANs is slightly higher than standard physical interfaces.
Interface and Hardware Component Configuration Guide for Cisco NCS 6000 Series Routers, IOS XR Release 6.4.x
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Configuring Link Bundling