Monitoring Bandwidth Usage: A Guide For Cisco Routers

Monitoring bandwidth usage on a Cisco router can be done in several ways. One method is to use the command show interface [interface], which displays statistics for a specific interface, including input and output rates. Another approach is to utilise NetFlow, a protocol supported by most enterprise Cisco devices, which allows for the export of flow data to a NetFlow Collector. Additionally, Cisco offers its own bandwidth monitoring software, the NetFlow Analyzer, which provides extensive insights into network traffic and bandwidth utilisation.

Utilise the 'show interface' command

Utilising the 'show interface' command is a great way to monitor bandwidth usage on a Cisco router. This command provides valuable insights into the performance of your network and helps identify potential issues. Here's a detailed guide on how to use this command effectively:

Understanding the 'show interface' Command

The 'show interface' command is a powerful tool that displays information about a specific interface on your Cisco router. This includes various statistics and parameters that can help you monitor bandwidth usage. By using this command, you can gain insights into the input and output rates, packet counts, errors, and other relevant metrics.

Getting Started with the 'show interface' Command

To use the 'show interface' command, simply type the following in your Cisco router's command-line interface:

Show interface [interface-type interface-number]

Replace `[interface-type interface-number]` with the specific interface you want to monitor. For example, if you want to monitor `FastEthernet0/1`, your command would be:

Show interface FastEthernet0/1

Analysing the Output

Once you execute the 'show interface' command, you will be presented with a wealth of information. Here's a breakdown of some key metrics to focus on:

• Input and Output Rates: These values represent the amount of data entering and exiting the interface, typically measured in bits per second (bps). They provide a clear indication of the bandwidth utilisation.
• Packets: This section displays the number of packets received and transmitted by the interface. It includes details such as unicast, broadcast, and multicast packets.
• Errors and Discards: The 'show interface' command also provides information on errors and discards. Errors occur when packets are corrupted or fail to reach their destination. Discards refer to packets that are intentionally dropped due to congestion or other issues.
• Queueing Strategy: This indicates how the router handles packet queuing. Common strategies include First-In-First-Out (FIFO) and Priority Queuing.

Customising the Output

You can customise the output of the 'show interface' command to focus on specific metrics. For example, to view only the input and output rates, you can use the following command:

Show interface [interface-type interface-number] | include bits

This command will display only the lines containing the word "bits", which typically refer to the input and output rates.

Monitoring Over Time

To monitor bandwidth usage over time, you can adjust the load interval using the 'load-interval' command. By default, the load interval is set to 5 minutes. However, you can change it to a shorter interval, such as 30 seconds, to get more frequent updates:

Load-interval 30

By utilising the 'show interface' command and its various options, you can effectively monitor bandwidth usage on your Cisco router. This command provides real-time insights that can help you optimise your network performance and troubleshoot any issues that may arise.

Use SNMP or Netflow

SNMP (Simple Network Management Protocol) and NetFlow are two tools that can be used to monitor bandwidth usage on a Cisco router. They both collect data on network traffic and provide insights into bandwidth consumption, but they have some key differences.

SNMP uses MIB (Management Information Base) variables to collect information about network devices, including bandwidth usage. It relies on polling, where it periodically collects data from the devices. SNMP can be used to monitor bandwidth utilisation on a Cisco router by collecting data on the number of octets transmitted and received, and calculating the percentage of bandwidth utilisation. This can be done using specific formulas provided by Cisco.

NetFlow, on the other hand, is a flow-based monitoring tool. It collects data on network traffic by analysing flows of packets between devices. NetFlow can be configured on Cisco routers to export flow data to a NetFlow Collector, which can then be used to analyse bandwidth usage. NetFlow provides detailed information about network traffic, including top conversations, protocols, applications, and talkers. It can also be used in conjunction with other tools like MRTG to monitor traffic counters for specific ports.

When deciding between SNMP and NetFlow, it's important to consider the specific requirements and constraints of your network. SNMP is widely supported and can provide basic bandwidth utilisation information. However, it may not accurately reflect the speed of a WAN interface and requires polling, which can impact the performance of the network devices. NetFlow, on the other hand, provides more detailed information about network traffic and can be more accurate, especially for full-duplex connections. However, it requires additional configuration and may be more resource-intensive.

In summary, both SNMP and NetFlow can be used to monitor bandwidth usage on a Cisco router, but they have different features and considerations. SNMP is simpler and more widely supported, while NetFlow provides more detailed traffic information and may be more accurate for certain connection types. The choice between the two depends on the specific needs and constraints of your network infrastructure.

Set load-interval to 30 seconds

Setting the load-interval to 30 seconds on a Cisco router allows network administrators to monitor bandwidth usage more efficiently. By default, the load-interval is set to 5 minutes, but this can be adjusted to provide a more granular view of network traffic.

The load-interval command in Cisco IOS defines the timeframe used to calculate interface load statistics. Reducing the interval to 30 seconds offers several advantages. Firstly, it provides increased reactivity, allowing administrators to identify short bursts of high traffic that might be missed with a longer interval. This is especially useful for troubleshooting network congestion caused by applications like video conferencing or real-time data feeds.

Secondly, with a shorter load-interval, administrators can troubleshoot issues faster as they have a more up-to-date picture of the interface load. This dynamic view is beneficial in rapidly changing network environments. Additionally, in network labs where network behaviour is accelerated, a 30-second load-interval provides a more accurate representation of traffic patterns within the compressed timeframe.

However, there are also considerations to keep in mind when setting a shorter load-interval. Calculating statistics more frequently consumes additional processing power, which might impact older or resource-constrained routers or switches. While a 30-second interval captures short-term fluctuations, it may obscure long-term trends, making it challenging for administrators to identify sustained load issues.

Additionally, the heightened sensitivity of monitoring with a shorter interval may result in false alarms, triggering unnecessary alerts or troubleshooting efforts due to short-term spikes in traffic. Therefore, it is important to carefully assess the specific needs and limitations of the network before setting a shorter load-interval.

Use a third-party application like LibreNMS

LibreNMS is a community-based, GPL-licensed autodiscovering network monitoring system. It can be used to monitor bandwidth usage on a Cisco router by polling real-time traffic data. This can be done as quickly as every 0.25 seconds, providing a more accurate view of bandwidth usage than the default 5-minute interval offered by Cisco.

To set up LibreNMS for Cisco router bandwidth monitoring, follow these steps:

• Install LibreNMS on a compatible Linux distribution, such as CentOS7.
• Configure your Cisco router to allow LibreNMS to access its data. This may involve setting up SNMP (Simple Network Management Protocol) credentials or enabling NetFlow, a feature that allows the router to export flow data to a collector.
• In LibreNMS, create an account and add your Cisco router as a device. Provide the necessary credentials and IP address for the router.
• Navigate to the "Interface Monitoring" section of LibreNMS and select the specific interface you want to monitor. This could be a particular VLAN or port channel.
• Set the polling interval to your desired frequency. Keep in mind that shorter intervals may impact the performance of the router and LibreNMS.
• Visualise the bandwidth usage data in LibreNMS. It provides graphs and charts to help you understand the utilisation rates over time.

By using LibreNMS, you can gain valuable insights into the bandwidth usage of your Cisco router. This information can be used to identify bottlenecks, troubleshoot performance issues, and optimise your network infrastructure. Additionally, LibreNMS offers alert rules that can notify you when certain thresholds are met, helping you proactively manage your network.

Monitor critical network metrics

Monitoring critical network metrics is essential for maintaining optimal network performance and preventing potential bottlenecks. Here are some methods and tools to achieve this in the context of Cisco routers:

NetFlow

NetFlow is a traditional way to monitor bandwidth usage by host. Most enterprise Cisco gear supports exporting NetFlow records, which can then be analysed to understand traffic patterns and identify high-consumption devices. NetFlow can be configured on Cisco routers to export flow data to a NetFlow Collector, with various software packages available, such as PRTG, ranging from free to expensive.

SNMP

Simple Network Management Protocol (SNMP) is another method to monitor bandwidth usage. SNMP can be used to retrieve the correct throughput Object Identifier (OID) and poll the network management platform in real-time or at specific intervals. SNMP can be integrated with network management platforms that visualise data through graphs.

Cisco Commands

Using specific commands on Cisco routers can provide valuable insights into bandwidth usage. For example, the "show interface summary" command displays bandwidth utilisation for each interface, VLAN, and port channel. It also offers the option to measure in bits per second (RXBS/TXBS fields) or packets per second (RXPS/TXPS fields). Additionally, the "show interface gi1/0/40" command is useful for troubleshooting as it provides bandwidth utilisation for a specific switch interface.

Third-Party Tools

Third-party tools, such as LibreNMS, can be employed to monitor real-time traffic. LibreNMS can poll traffic data as frequently as every 0.25 seconds, providing detailed insights into network utilisation.

Medianet & Mediatrace Monitoring

NetFlow Analyzer is a tool that supports extensive Cisco-based environment monitoring, including routers, switches, WLCs, and firewalls. It collects and analyses flow data (NetFlow/IPFIX) exported from Cisco devices, offering detailed reports on network traffic, top conversations, protocols, applications, and talkers. NetFlow Analyzer also supports Medianet & Mediatrace Monitoring, providing additional insights into critical network metrics.

Frequently asked questions