Interface Reporting

Digital network interfaces use serial transmission to send data from the transmission port to the receive port on the other end of the communications channel or circuit. Some transmission channels, such as copper Gigabit Ethernet, aggregate serial data across multiple channels to establish their overall circuit capacity. For copper Gigabit Ethernet, 4 channels of 250 Mbps are used to establish the 1-Gbps Ethernet circuit.
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Digital network interfaces use serial transmission to send data from the transmission port to the receive port on the other end of the communications channel or circuit. Some transmission channels, such as copper Gigabit Ethernet, aggregate serial data across multiple channels to establish their overall circuit capacity. For copper Gigabit Ethernet, 4 channels of 250 Mbps are used to establish the 1-Gbps Ethernet circuit.
Most digital interfaces are
full-duplex.
The term means that they can transmit outbound data at the same moment that they are receiving inbound data. Because data transmission and data reception are independent interface tasks, they are reported separately.
Interface Utilization represents the average amount of data that is transmitted by the interface in a single direction (In or Out), divided by the interface bandwidth, or capacity. Interface utilization can be expressed as a percentage or as a transmission rate in bits per-second (bps).
Interface utilization rates can contribute to network performance issues. For a given interface, monitor whether it is transmitting frames at or below the rate at which it is receiving them. Acceptable interface utilization rates also depend on various SLAs and failover scenarios within your network. For example, two interfaces use a load-sharing algorithm to balance outbound traffic to the next hop. The average interface utilization must remain low enough that a failure of one link does not saturate the remaining available link, which now transmits all data.
Interface Utilization
Interface utilization
 refers to the transmission and reception of data and associated framing of device interfaces. Interface utilization is commonly referred to as "network utilization," "circuit utilization," or "uplink utilization."
The interface utilization percentage metric is calculated from average data because an instantaneous reading of individual interface utilization is either 100% (actively transmitting or receiving a frame) or 0% (not actively transmitting/receiving a frame). The average utilization percentage value includes the amount of time that the interface was in use over the given interval.
The interface utilization rate metric takes into account the interface speed, or its available bandwidth. For a physical interface, the available bandwidth of an interface is defined as the actual clockspeed rate at which the interface is capable of transmitting data. For example, 1536 Kbps, 44.728 Mbps, 100 Mbps, 1 Gbps, and 10 Gbps describe clockspeed rates. For logical interfaces, such as subinterfaces, the available bandwidth is defined as the bandwidth value assigned to the interface by a network administrator. However, the total amount of real bandwidth available to the logical interfaces cannot exceed the physical interface capacity in terms of actual transmission rates.
Full-duplex interfaces have the capability to transmit data independently at the same time that they can receive data. This capability requires independent hardware dedicated in the transmit direction and the receive direction of the
 
interface. Accordingly, the average utilization of an interface is reported separately in either the inbound or outbound direction. For example, separate views show "Average Utilization Out" and "Average Utilization In".
The network utilization can be derived from interface utilization values averaged over time from interfaces that are in use or not in use.
Interface Errors and Discards
Elevated interface error rates usually indicate a problem with the transmission medium. For example, the cable, fiber, or interface hardware can cause errors. Each error indicates that the associated packet was dropped during the attempt to transmit or receive it.
When detected in the inbound direction, errors typically indicate problems with the transmission medium (for example, cable or fiber). Outbound errors indicate problems with the interface hardware. The acceptable rate of errors for any given interface is typically zero (0) errors.
Interface discards typically occur when interface buffers no longer have the capacity to store packets (because, for example, buffer memory is exhausted). Buffer congestion often indicates that the rate at which packets are arriving at the interface exceeds its transmission rate.
Each reported discard is a packet that the reporting interface threw out. The sending host must retransmit such packets if a reliable protocol such as TCP is used to send the data end-to-end. Interface discards are typically the result of congested queues serving the interface. Discards frequently occur in bursts. Elevated discard rates may be the result of either microcongestion or chronic congestion issues.
Acceptable discard rates depend on the applications being served, the transmission protocols, and the SLAs established within your organization. Views of interface error and discard totals use a "k" to indicate thousands. Units labeled 'kErrors' or 'kDiscards' therefore refer to thousands of packet errors or thousands of packet discards.
Interface Bandwidth
The term "bandwidth" generally refers to the available capacity of an interface to transmit data at a given bit rate. The bandwidth associated with an interface depends on the type of interface.
For a physical interface, the bandwidth is the physical clock rate that the interface uses to transmit data. The clock rate is also typically a function of the type of interface. The following list shows the clock rates for common physical interfaces:
  • DS-0: 64 Kbps
  • DS-1: 1.536 Mbps
  • E-1: 2.048 Mbps
  • E-3: 34.368 Mbps
  • DS-3: 44.278 Mbps
  • OC-3: 155 Mbps
  • Fast Ethernet: 100 Mbps
  • Gigabit Ethernet: 1000 Mbps
  • Ten Gigabit Ethernet: 10 Gbps