Link Bundling Overview; Load Balancing - Cisco ASR 9000 Series Configuration Manual
Aggregation services router modular quality of service
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- Command reference manual (1138 pages) ,
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Link Bundling Overview
Link Bundling Overview
The Link Bundling feature allows you to group multiple point-to-point links together into one logical link
and provide higher bidirectional bandwidth, redundancy, and load balancing between two routers. A virtual
interface is assigned to the bundled link. The component links can be dynamically added and deleted from
the virtual interface.
The virtual interface is treated as a single interface on which one can configure an IP address and other software
features used by the link bundle. Packets sent to the link bundle are forwarded to one of the links in the bundle.
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:
• Multiple links can span several line cards to form a single interface. Thus, the failure of a single link
• Bundled interfaces increase bandwidth availability, because traffic is forwarded over all available
All the individual links within a single bundle must be of the same type and the same speed.
Cisco IOS XR software supports these methods of forming bundles of Ethernet interfaces:
• IEEE 802.3ad—Standard technology that employs a Link Aggregation Control Protocol (LACP) to
• EtherChannel —Cisco proprietary technology that allows the user to configure links to join a bundle,
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.
Cisco ASR 9000 Series Aggregation Services Router Modular Quality of Service Configuration Guide, Release
6.1.x
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does not cause a loss of connectivity.
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..
ensure that all the member links in a bundle are compatible. Links that are incompatible or have failed
are automatically removed from a bundle.
but has no mechanisms to check whether the links in a bundle are compatible.
Configuring Modular QoS on Link Bundles
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