Routing with External Endpoints
An external endpoint is a WAE Design object that identifies specific entry (source) or exit (destination) points for demands. These are identified in the External Endpoints table by a name and an optional tag.
Each external endpoint consists of one or more members that are defined as nodes, external ASes, or a combination of an external AS and external node. By setting a demand’s source or destination to an external endpoint, you can simulate traffic going from multiple sources to a single destination, from a single source to multiple destinations, or multiple sources going to multiple destinations. Because of this flexibility, they are useful for specifying secondary entry and exit points in the event of failures.
External Endpoint Members
Each member is assigned properties that prioritize traffic entering and exiting that member, in what order to fail over to another member, and how to distribute traffic for members of equal priority. These properties are set when you create the member, and all members are listed in the External Endpoint Members table.
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Member Endpoint—Defines whether the member is a node, AS, or external node via an AS.
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Priority—The sequential order in which external endpoint members are used in the simulations should failures occur.
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Equal priority routing—If members have the same priority, this property identifies how the traffic is distributed.
Note |
Members within an external endpoint that have the same priority must either all be Shortest Path or none of them be Shortest Path. |
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Shortest Path—Use the member that results in the use of shortest path between source and destination.
If a member is using a shortest path, the Traffic Balance (%) column in the External Endpoint Members table shows “na.”
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Fix Traffic—Set the traffic across members of equal priority as defined in the Traffic Balance (%) field.
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Deduce Traffic—Behaves the same as Fix Traffic in that it sets traffic across members of equal priority as defined in the Traffic Balance (%) field. However, upon running Demand Deduction, the Traffic Balance (%) field is updated based on the measured traffic in the network. Note that Demand Deduction only estimates the traffic balances for external endpoints with a priority that is in use in the current no-failure simulation. Thus, Deduce Traffic is usually set to Priority 1.
Routing Simulations
Note |
Although this section describes demands as being sourced from an external endpoint, the same methodology holds true if a demand’s destination is an external endpoint. |
If a demand’s source is defined as an external endpoint, the following selection of external endpoint members ensues.
Procedure
Step 1 |
Members with the highest priority (lowest number) are used as the demand’s source. For example, if the external endpoint has two members with a priority of 1, the demand is sourced from both members provided they are available. If one or more of the members are not available, the traffic from the unavailable members is evenly redistributed to the other top priority members. |
Step 2 |
If none of the top priority members are available to source the traffic but there are next-priority members available, Step 1 is repeated for the next priority external endpoint members. Only if all members with the same priority fail does the traffic get routed according to the next priority in the sequence. Note that if a failure occurs that does not affect the external endpoint member’s ability to send or receive traffic, then traffic is rerouted as usual without a need to use the additional members. If an external endpoint member is an external AS, with or without a node specified, then the routing from or to that member is determined by the BGP routing policy determined by the AS relationships. The distribution of traffic between external endpoints with the same priority is the same as for node members. |
Traffic Distribution
The traffic distribution through these demands is based on the Equal Priority Routing property, and if applicable, the Traffic Balance (%) property used to define the external endpoint members.
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If there is only one member and it is defined as Shortest Path, the demand takes the shortest path as defined by the IGP metrics.
Of the routable demands, if the Traffic Balance (%) values are all empty, the traffic is routed and equally load balanced across the demands with the shortest IGP paths. Note in the case of multiple internal ASes, the shortest IGP route is the shortest route in the first AS the demand enters.
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If multiple members of the same priority are set to Shortest Path, the demand takes the path with the shortest IGP path. If all interfaces between the source members and the destination have the same shortest IGP paths, then the traffic is load balanced equally across them.
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If one or more members of the same priority have their Equal Priority Routing property set to Fix Traffic or Deduce Traffic, the demand traffic is split according to each member’s Traffic Balance (%) value.
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If the Traffic Balance percentages across sources with the same priority sum to less than 100%, the overall demand traffic is decreased to that percentage.
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If an external endpoint member of the same priority fails, the traffic on the remaining members increases in proportion, so that the same amount of traffic is still routed.
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Example: Node A failed. Nodes B, C, and D each have a priority of 2 and are each a Fix Traffic type. Their traffic balances are 20%, 20%, and 40%, respectively. The demand has 1000 Mbps of traffic.
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Because Node A failed, the demand routes 200 Mbps traffic through node B, 200 Mbps through C, and 400 Mbps through D, totaling 800 Mbps (Example Effect of Failures When Using External Endpoints).
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If Node D fails, the demand routes 400 Mbps traffic through Node B and 400 through C. If Node B fails too, the entire 800 Mbps is routed through C (Example Effect of Failures When Using External Endpoints).
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If all three priority 2 members fail, 1000 Mbps is routed through node E, which is the priority 3 member (Example Effect of Failures When Using External Endpoints).