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
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
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.
without interrupting packet flow.
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
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.
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
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-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
Only Per-Destination Load
Balancing is supported.
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.
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:
All Quality of Service (QoS) features, currently supported on
physical interfaces and subinterfaces, are also supported on all Link Bundle
interfaces and subinterfaces. QoS is configured on Link Bundles in the same way
that it is configured on individual interfaces. However, the following points
should be noted:
When a QoS policy is applied
on a bundle (ingress or egress directions), the policy is applied at each
member interface. Any queues and policers in the policy map (ingress or egress
directions) will be replicated on each bundle member.
If a QoS policy is not
applied to a bundle interface or bundle VLAN, both the ingress and egress
traffic will use the per link members port default queue.
Link bundle members may
appear across multiple Network Processing Units and linecards. The shape rate
specified in the bundle policymap is not an aggregate for all bundle members.
The shape rate applied to the bundle will depend on the load balancing of the
links. For example, if a policy map with a shape rate of 10 Mbps is applied to
a bundle with two member links, and if the traffic is always load-balanced to
the same member link, then an overall rate of 10 Mbps will apply to the bundle.
However, if the traffic is load-balanced evenly between the two links, the
overall shape rate for the bundle will be 20 Mbps.
Example 1 shows how a
traffic policy is applied on an Ethernet link bundle, in the ingress direction.
The policy is applied to all interfaces that are members of the Ethernet link
Example 1 Applying a Traffic Policy to an Ethernet Link Bundle
interface Bundle-Ether bundle-id
service-policy input policy-1
QoS for POS link bundling
For POS link bundles,
percentage-based bandwidth is supported for policers and output queues.
Time-based queue limit is supported for output queues.
For input QoS, queuing is not supported and thus bandwidth is used for policer only. As a member link is added or removed from a bundle with input QoS configured, the aggregate bundle bandwidth for that affected line card will change. One input QoS policy instance is assigned for each SIP 700 line card that is part of the POS link bundle.
Output QoS Policy setup
Example 2 : Output QoS policy supported on POS link
When a member link is added
to a bundle with output QoS configured, the policy-map of the bundle is applied
to the member link.
Example 2 shows the output
QoS policy supported on POS link bundles.
priority level 1
police rate percent 10
bandwidth percent 30
queue-limit 100 ms
queue-limit 100 ms
These sections provide
references related to implementing QoS on Link Bundles.
No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature.
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