IP SLAs test packets use time stamping to minimize the processing delays. When the IP SLAs responder is enabled, it allows the target device to take time stamps when the packet arrives on the interface at interrupt level and again just as it is leaving, eliminating the processing time. This time stamping is made with a granularity of sub-milliseconds ms.
Figure demonstrates how the responder works. Four time stamps are taken to make the calculation for round-trip time. At the target router, with the responder functionality enabled, time stamp 2 TS2 is subtracted from time stamp 3 TS3 to produce the time spent processing the test packet as represented by delta. This delta value is then subtracted from the overall round-trip time. Notice that the same principle is applied by IP SLAs on the source router where the incoming time stamp 4 TS4 is also taken at the interrupt level to allow for greater accuracy.
An additional benefit of the two time stamps at the target device is the ability to track one-way delay, jitter, and directional packet loss. Because much network behavior is asynchronous, it is critical to have these statistics. However, to capture one-way delay measurements, you must configure both the source router and target router with Network Time Protocol NTP so that the source and target are synchronized to the same clock source.
One-way jitter measurements do not require clock synchronization. When you configure an IP SLAs operation, you must schedule the operation to begin capturing statistics and collecting error information. You can schedule an operation to start immediately or to start at a certain month, day, and hour.
You can use the pending option to set the operation to start at a later time. The pending option is an internal state of the operation that is visible through SNMP. The pending state is also used when an operation is a reaction threshold operation waiting to be triggered. Scheduling the operations to run at evenly distributed times allows you to control the amount of IP SLAs monitoring traffic.
To support successful service level agreement monitoring, you must have mechanisms that notify you immediately of any possible violation. Determining the type of threshold and the level to set can be complex, and depends on the type of IP service being used in the network.
It does include several operations as examples, including configuring the responder, configuring UDP jitter operation, which requires a responder, and configuring ICMP echo operation, which does not require a responder. Note that not all of the IP SLAs commands or operations described in this guide are supported on the switch. It does not support VoIP service levels using the gatekeeper registration delay operations measurements. This is an example of the output from the command:.
Optional Save your entries in the configuration file. Jitter means interpacket delay variance. When multiple packets are sent consecutively 10 ms apart from source to destination, if the network is behaving correctly, the destination should receive them 10 ms apart. But if there are delays in the network like queuing, arriving through alternate routes, and so on the arrival delay between packets might be more than or less than 10 ms with a positive jitter value meaning that the packets arrived more than 10 ms apart.
If the packets arrive 12 ms apart, positive jitter is 2 ms; if the packets arrive 8 ms apart, negative jitter is 2 ms. For delay-sensitive networks, positive jitter values are undesirable, and a jitter value of 0 is ideal. The packets IP SLAs generates carry packet sending and receiving sequence information and sending and receiving time stamps from the source and the operational target. Based on these, UDP jitter operations measure this data:. Because the paths for the sending and receiving of data can be different asymmetric , you can use the per-direction data to more readily identify where congestion or other problems are occurring in the network.
The UDP jitter operation generates synthetic simulated UDP traffic and sends a number of UDP packets, each of a specified size, sent a specified number of milliseconds apart, from a source router to a target router, at a given frequency. By default, ten packet-frames, each with a payload size of 10 bytes are generated every 10 ms, and the operation is repeated every 60 seconds. You can configure each of these parameters to best simulate the IP service you want to provide.
To provide accurate one-way delay latency measurements, time synchronization, such as that provided by NTP, is required between the source and the target device. Time synchronization is not required for the one-way jitter and packet loss measurements.
If the time is not synchronized between the source and target devices, one-way jitter and packet loss data is returned, but values of 0 are returned for the one-way delay measurements provided by the UDP jitter operation. The range is from 1 to seconds; the default is 60 seconds. Exit UDP jitter configuration mode, and return to global configuration mode. If no month is entered, the default is the current month. Response time is computed by measuring the time taken between sending an ICMP echo request message to the destination and receiving an ICMP echo reply.
Display configuration values including all defaults for all IP SLAs operations or a specific operation. Display enhanced history statistics for collected history buckets or distribution statistics for all IP SLAs operations or a specific operation. Display the configured proactive threshold monitoring settings for all IP SLAs operations or a specific operation. Display current or aggregated operational status and statistics. Skip to content Skip to search Skip to footer. Book Contents Book Contents.
Find Matches in This Book. Log in to Save Content. PDF - Complete Book Updated: September 11, You can use the simulator tool: — for network assessment before deploying applications that have stringent network performance requirements.
When the alternate port receives the failure notification, it changes to the open state, forwarding all VLANs. A regular segment port converted to an edge port, or an edge port converted to a regular segment port, does not always result in a topology change. If you convert an edge port into a regular segment port, VLAN load balancing is not implemented unless it has been configured. For VLAN load balancing, you must configure two edge ports in the segment.
A segment port that is reconfigured as a spanning tree port restarts according the spanning tree configuration. By default, this is a designated blocking port. A segment is a collection of ports connected one to the other in a chain and configured with a segment ID. You should configure two edge ports in the segment, with one of them the primary edge port and the other by default the secondary edge port.
A segment has only one primary edge port. If you configure two ports in a segment as the primary edge port, for example, ports on different switches, the REP selects one of them to serve as the segment primary edge port.
REP is disabled on all interfaces. When enabled, the interface is a regular segment port unless it is configured as an edge port. When VLAN load balancing is enabled, the default is manual preemption with the delay timer disabled. We recommend that you begin by configuring one port and then configure contiguous ports to minimize the number of segments and the number of blocked ports. If more than two ports in a segment fail when no external neighbors are configured, one port goes into a forwarding state for the data path to help maintain connectivity during configuration.
When the external neighbors for the failed ports are configured, the ports go through the alternate port state transitions and eventually go to an open state or remain as the alternate port, based on the alternate port selection mechanism. We recommend that you configure all trunk ports in the segment with the same set of allowed VLANs. Be careful when configuring REP through a Telnet connection. You might lose connectivity to the router if you enable REP in a Telnet session that accesses the router through the same interface.
You must configure all trunk ports in the segment with the same set of allowed VLANs, or a misconfiguration occurs. There is no limit to the number of REP ports on a switch; however, only two ports on a switch can belong to the same REP segment. If only one port on a switch is configured in a segment, the port should be an edge port. If two ports on a switch belong to the same segment, they must be both edge ports, both regular segment ports, or one regular port and one edge no-neighbor port.
An edge port and regular segment port on a switch cannot belong to the same segment. If two ports on a switch belong to the same segment and one is configured as an edge port and one as a regular segment port a misconfiguration , the edge port is treated as a regular segment port. REP interfaces come up in a blocked state and remain in a blocked state until they are safe to be unblocked. You need to be aware of this status to avoid sudden connection losses. You can configure how long a REP interface remains up without receiving a hello from a neighbor.
You can use the rep lsl-age-timer value interface configuration command to set the time from ms to ms. The LSL hello timer is then set to the age-timer value divided by 3. In normal operation, three LSL hellos are sent before the age timer on the peer switch expires and checks forhello messages.
EtherChannel port channel interfaces do not support LSL age-timer values less than ms. If you try to configure a value less than ms on a port channel, you receive an error message and the command is rejected. There can be a maximum of 64 REP segments per switch. To avoid the delay introduced by relaying messages in the software for link-failure or by VLAN-blocking notifications during load balancing, the REP floods packets to a regular multicast address at the hardware flood layer HFL.
These messages are flooded to the whole network, not just the REP segment. You can control flooding of these messages by configuring an administrative VLAN for the whole domain. There can be only one administrative VLAN on a switch and on a segment. However, this is not enforced by software. Specifies the administrative VLAN. The range is 2 to The default is VLAN 1. To set the admin VLAN to 1, enter the no rep admin vlan global configuration command. This task is required and must be done before other REP configurations.
You must also configure a primary and secondary edge port on each segment. All other steps are optional. Follow these steps to enable and configure REP on an interface:. Enables privileged EXEC mode. Enter your password if prompted.
Specifies the interface, and enter interface configuration mode. The interface can be a physical Layer 2 interface or a port channel logical interface. The port-channel range is 1 to Configures the interface as a Layer 2 trunk port. Enables REP on the interface and identifies a segment number.
The segment ID range is from 1 to These optional keywords are available:. You must configure two edge ports, including one primary edge port for each segment. Optional edge —Configures the port as an edge port. Each segment has only two edge ports. Entering the edge without the primary keyword configures the port as the secondary edge port.
Optional primary —Configures the port as the primary edge port, the port on which you can configure VLAN load balancing. Optional no-neighbor —configures a port with no external REP neighbors as an edge port. The port inherits all properties of edge ports, and you can configure them the same as any edge port.
Although each segment can have only one primary edge port, if you configure edge ports on two different switches and enter the primary keyword on both switches, the configuration is valid. However, REP selects only one of these ports as the segment primary edge port. You can identify the primary edge port for a segment by entering the show rep topology privileged EXEC command.
Optional preferred —Indicates that the port is the preferred alternate port or the preferred port for VLAN load balancing. Configuring a port as preferred does not guarantee that it becomes the alternate port; it merely gives the port a slight edge over equal contenders. The alternate port is usually a previously failed port.
The range is from 1 to The port ID is automatically generated for each port in the segment. The range is from to , with negative numbers indicating the downstream neighbor from the secondary edge port. A value of 0 is invalid. Enter -1 to identify the secondary edge port as the alternate port.
See Figure 1 for an example of neighbor offset numbering. Because you enter this command at the primary edge port offset number 1 , you cannot enter an offset value of 1 to identify an alternate port. Enter this command only on the REP primary edge port. Optional Configures a preempt time delay. Use this command if you want VLAN load balancing to automatically trigger after a link failure and recovery.
The time delay range is between15 to seconds. The default is manual preemption with no time delay. Optional Configures a time in milliseconds for which the REP interface remains up without receiving a hello from a neighbor. The range is from to ms in ms increments. The default is ms 5 seconds. Both ports on the link should have the same LSL-age configured to avoid link flaps.
Optional Displays the REP interface configuration. Optional Saves your entries in the router startup configuration file. If you do not enter the rep preempt delay seconds rep preempt delay seconds interface configuration command on the primary edge port to configure a preemption time delay, the default is to manually trigger VLAN load balancing on the segment.
Be sure that all other segment configuration has been completed before manually preempting VLAN load balancing. When you enter the rep preempt delay segment-id command, a confirmation message appears before the command is executed because preemption can cause network disruption. Manually triggers VLAN load balancing on the segment.
You will need to confirm the command before it is executed. Enables the switch to send REP traps, and sets the number of traps sent per second. Enter the number of traps sent per second. The range is from 0 to The default is 0 no limit imposed; a trap is sent at every occurrence. Optional Displays the running configuration, which can be used to verify the REP trap configuration. Optional Saves your entries in the switch startup configuration file.
Displays REP configuration and status for an interface or for all interfaces. Optional detail —displays interface-specific REP information. Displays REP topology information for a segment or for all segments, including the primary and secondary edge ports in the segment.
Optional archive —displays the last stable topology. Optional detail —displays detailed archived information. This example shows how to configure the administrative VLAN as VLAN and verify the configuration by entering the show interface rep detail show interface rep detail command on one of the REP interfaces:. This example shows how to configure an interface as the primary edge port for segment 1, to send STCNs to segments 2 through 5, and to configure the alternate port as the port with port ID D to block all VLANs after a preemption delay of 60 seconds after a segment port failure and recovery.
The interface is configured to remain up for milliseconds without receiving a hello from a neighbor. This example shows how to configure the same configuration when the interface has no external REP neighbor:. This example shows how to configure the VLAN blocking configuration shown in the figure below. The alternate port is the neighbor with neighbor offset number 4. To help you research and resolve system error messages in this release, use the Error Message Decoder tool.
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Skip to content Skip to search Skip to footer. Book Contents Book Contents. Find Matches in This Book. Log in to Save Content. PDF - Complete Book Updated: November 7, Chapter: Configuring Resilient Ethernet Protocol. Figure 1. REP Open Segment The segment shown in the figure above is an open segment; there is no connectivity between the two edge ports.
Figure 2. Figure 3. Edge No-Neighbor Ports REP has these limitations: You must configure each segment port; an incorrect configuration can cause forwarding loops in the networks. A segment port does not become operational if: No neighbor has the same segment ID. More than one neighbor has the same segment ID. The neighbor does not acknowledge the local port as a peer. When you configure VLAN load balancing, you can specify the alternate port in one of three ways: By entering the port ID of the interface.
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