Frame Relay

This section discusses issues surrounding the management of Frame Relay on Cisco routers.

How Can I Measure the Number of Frame Relay Drops that Occur?

Tracking Frame Relay drops allows you to monitor speed mismatch congestion on the router DTE output queue. Keep in mind that there is no way to track drops in the service provider network.

From CISCO-FRAME-RELAY-MIB, CfrCircuitDropPktsOuts indicates the number of drops on a given Frame Relay circuit.

For more information, please see "MIBs to Monitor for Packet Discards" in Chapter 16, "Monitoring WAN Technologies Frame Relay."

How Do I Measure Frame Relay Circuit Utilization?

Tracking Frame Relay DLCI utilization is similar to tracking the utilization for other types of interfaces in that you track traffic transmitted and received by an interface and compare it with a maximum amount capable.

However, unlike other interfaces, other factors affect the throughput for a particular Frame Relay circuit. For example, CIR, burst rate, and service provider network congestion can affect your ability to accurately calculate utilization.

There are two methods for calculating Frame Relay circuit utilization. The first involves using the frCircuitSentOctets and frCircuitReceivedOctets from RFC 1315. This method measures the in and out octets for each circuit (DLCI). As long as you are not using compression over the circuit, the counters are accurate.

However, you can also gather ifInOctets and ifOutOctets from RFC 2233 for each Frame Relay sub-interface. The advantage of this method is that these counters take into consideration the compressed data statistics rather than the uncompressed.

For more information, please see the following sections:

• "Measuring Utilization on Virtual Circuits" in Chapter 16

• "Performance Monitoring for System Interfaces" in Chapter 12

• "Utilization" in Chapter 4

How Can I Detect if a Frame Relay PVC Changes State?

Have your router generate the frDLCIStatusChange trap from RFC 1315. The trap is generated whenever a PVC changes state. The three possible states are the following:

• Invalid

• Active

• Inactive

You can also get the current state via SNMP by polling the frCircuitState variable from RFC 1315.

Keep in mind that in most service providers' networks, Frame Relay LMI is not end-to-end and that the service provider's switch may not accurately report the loss of a PVC.

For more information, please see "Error/Fault Data for Frame Relay" in Chapter 16.