FIELD

The present application relates to communications methods and, more particularly, to methods and apparatus for determining and communicating link and/or link bundle information which can be used for making routing decisions.

BACKGROUND

Link metrics, often referred to as link weights, are sometimes advertised and used in a communications network by devices trying to make routing decisions with regard to which path to use. For example, in the case of shortest path first routing, link metrics indicative of path length are advertised and routing decisions are made based on the advertised link metrics, e.g., with the links which result in the lowest cumulative link metric between a source device and destination device being selected for inclusion in a route between the source and destination device. In other cases where the link metrics represent cost metrics, the advertised link metrics are normally indicative of a cost associated with a link. In a cost based approach to routing a device will normally select the lowest cost path as indicated by selecting a path with the lowest overall cost as indicated by the cumulative sum of the link metrics of each link in the selected path.

Link aggregation allows multiple links, e.g., Ethernet links, into a single logical link between two networked devices. An aggregation of links is often referred to as a bundle. For purposes of advertising a link metric, the logical link is treated as a single link even though it represents a bundle of individual links. Accordingly, a single link metric is normally advertised for a bundle.

Link Aggregation Control Protocol (LACP) is an IEEE standard defined in IEEE 802.3ad. LACP lets devices send Link Aggregation Control Protocol Data Units (LACPDUs) to each other to establish a link aggregation connection. The metric used to facilitate routing decisions is often communicated as a Link Aggregation Control Protocol Data unit.

A useful feature of LACP is that when one member link stops sending LACPDUs (if the cable is unplugged, for example), it is removed from the link aggregation group (LAG). This helps to minimize packet loss.

In the case of link bundles, it is often possible to configure a device to stop advertising a metric for a link bundle if the number of operational links in the bundle falls below a configured number of links, e.g., a number of links expected to be needed to support a normal or anticipated traffic load. Once a metric for the bundle ceases to be advertised, the bundle will normally be removed from the set of links which are considered by devices for routing purposes in accordance with the link protocol being used.

Removing a bundle which can no longer handle the expected normal traffic load reduces the risk of packet loss, e.g., due to overloading of a bundle which is suffering from one or more faulty connections or links which reduce its capacity. Networks are often designed with sufficient redundancy that if one link bundle fails another, e.g., redundant, link bundle will be able to handle the load.

While the removal of one bundle from a network from one or more link failures in the links which form the bundle may not have significant impact on a network, the failure of multiple bundles may result in a portion of a network being coming isolated.

In view of the above discussion it should be appreciated that there is a need for methods and/or apparatus which would allow a bundle to be removed from being used when a functional alternative bundle can serve as an alternative path for the full normal traffic flow but which would leave the bundle as an available link, albeit one that might not be able to support the full normal traffic flow, in cases where failure to use the one or more functional links in the bundle would result in a portion of a network becoming isolated due to the lack of a good alternative link or bundle.

SUMMARY

Methods and apparatus relating to the use of aggregated links, e.g., links in a bundle, are described. In accordance with various features when the number of links in a bundle drops below a predetermined number of links, e.g., a number of links which can and sometimes is set on a per bundle basis taking into consideration the number of functional links required to support the expected normal bundle traffic load of the bundle, a switch is made between advertising a normal bundle link metric to advertising a limited operation mode link bundle metric. In some embodiments, the predetermined number or links is 1 greater than the limited operation mode number of links. In some cases the limited operation mode link bundle metric is set to the maximum possible link metric value. While in some embodiments for normal operation the link metric is a metric based on path length or cost, in the case of limited operation mode the metric is one which is intended to discourage use of the bundle as a link. When the link metric value is set to the maximum possible value the faulty link bundle becomes a link of last resort since it will be perceived as the longest, most costly, or otherwise undesirable link in any set of possible links being considered for routing purposes since the link metric is set to the maximum possible value. In other embodiments the link metric advertised for a link in limited operation mode is a multiple of the normal link metric for the link bundle. Thus the link bundle will be less desirable from a routing perspective discoursing use of the bundle below what would be its normal level of use. In some embodiments the limited operation mode metric for a bundle is determined based on the number of links which remain available for use with the metric increasing in value as the number of links decreased from the threshold number used to trigger limited link mode operation.

While adverting a large link metric for a link bundle can significantly decrease the likelihood that a bundle will be used and in some cases makes the bundle a link of last resort, advertising a limited mode link metric for a faulty bundle unable to support its normal traffic load keeps the remaining links in the bundle available for use and can avoid a network segment from becoming isolated as might be the case if multiple partial bundle failures triggered nodes to stop advertising link metrics making the links of the bundles unavailable.

While in various embodiments the methods and apparatus are used in the context of Ethernet link bundles and LACP, the methods and apparatus can be used in wide range of communications networks and with various type of communications links which may be aggregated into a bundle and which can thus serve as a logical link between two network nodes.

An exemplary method of operating a first node in a communications network, in accordance with some embodiments, comprises: determining a normal link bundle metric for a first link bundle including a plurality of communications links between a first network node and a second network node; determining a limited operation mode link bundle metric for the first link bundle; and making a first link bundle metric advertising decision, said first link bundle metric advertising decision being a decision to: i) advertise the normal link bundle metric for the first link bundle; ii) advertise the limited operation mode link bundle metric for the first link bundle; or iii) perform no advertising of a link bundle metric for the first link bundle; and taking an advertising action in accordance with the determined first link bundle metric advertising decision, said advertising action including operating the first node to: i) advertise the normal link bundle metric for the first link bundle, ii) advertise the limited operation mode link bundle metric for the first link bundle or iii) control the first node to refrain from advertising a link bundle metric for the first link bundle.

While various features discussed in the summary are used in some embodiments it should be appreciated that not all features are required or necessary for all embodiments and the mention of features in the summary should in no way be interpreted as implying that the feature is necessary or critical for all embodiments.

Numerous additional feature and embodiments are described in the detailed description which follows.

