Load Balancing; Layer 3 Load Balancing On Link Bundles - Cisco ASR 9000 Series Service Configuration Manual

Load Balancing

A link bundle is simply a group of ports that are bundled together and act as a single link. The advantages
of link bundles are as follows:
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•
All the individual links within a single bundle must be of the same type and the same speed.
Cisco IOS XR software supports the following methods of forming bundles of Ethernet interfaces:
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•
Load Balancing
Load balancing is supported on all links in the bundle. Load balancing function is a forwarding
mechanism to distribute traffic over multiple links based on layer 3 routing information in the router.
There are two types of load balancing schemes:
• Per-Destination Load Balancing
• Per-Packet Load Balancing
When a traffic stream arrives at the router, per-packet load balancing allows the traffic to be evenly
distributed among multiple equal cost links. Per-packet schemes make routing decision based on
round-robin techniques, regardless of the individual source-destination hosts.
Only Per-Destination Load Balancing is supported.
Per-destination load balancing allows the router to distribute packets over one of the links in the bundle
to achieve load sharing. The scheme is realized through a hash calculating based on the
source-destination address and user sessions.
When the per-destination load balancing is enabled, all packets for a certain source-destination pair will
go through the same link, though there are multiple links available. In other words, per-destination load
balancing can ensure that packets for a certain source-destination pair could arrive in order.

Layer 3 Load Balancing on Link Bundles

By default, load balancing on Layer 2 link bundles is done based on the MAC SA/DA fields in the packet
header. Layer 3 load balancing for link bundles is done on Ethernet Flow Points (EFPs) and is based on
the IPv4 source and destination addresses in the packet.When Layer 3 service-specific load balancing is
configured, all egressing bundles are load balanced based on the IPv4 source and destination addresses.
When packets do not have IPv4 addresses, default load-balancing is used.
Layer 3 load balancing for link bundles is enabled globally, using the following command:
Cisco ASR 9000 Series Aggregation Services Router Modular Quality of Service Configuration Guide
QC-156
Multiple links can span several line cards to form a single interface. Thus, the failure of a single link
does not cause a loss of connectivity.
Bundled interfaces increase bandwidth availability, because traffic is forwarded over all available
members of the bundle. Therefore, traffic can flow on the available links if one of the links within a
bundle fails. Bandwidth can be added without interrupting packet flow.
IEEE 802.3ad—Standard technology that employs a Link Aggregation Control Protocol (LACP) to
ensure that all the member links in a bundle are compatible. Links that are incompatible or have
failed are automatically removed from a bundle.
EtherChannel —Cisco proprietary technology that allows the user to configure links to join a
bundle, but has no mechanisms to check whether the links in a bundle are compatible.
hw-module load-balance bundle l2-service l3-params
Configuring Modular QoS on Link Bundles on Cisco ASR 9000 Series Routers
OL-23108-02