of the target network. Various methods will be developed below. Tapping by software This type of tapping focuses on tapping by making use of software, and without making any significant change on an infrastructures hardware. This type of tapping is often the cheapest one to implement, but it needs several implementations to give a truly complete look of the network. Monitoring software The simplest type of monitoring is logging into an interesting device and running programs or commands that show performance statistics and other data. This is the cheapest way to monitor a network, and is highly appropriate for small networks. However, it does not scale well to large networks. It can also impact the network being monitored; see observer effect. SNMP Another way to monitor devices is to use a remote management protocol such as SNMP to ask devices about their performance. This scales well, but is not necessarily appropriate for all types of monitoring. The inherent problems with SNMP are the polling effect. Many vendors have alleviated this by using intelligent polling schedulers, but this may still affect the performance of the device being monitored. It also opens up a host of potential security problems. Port mirroring Another method to monitor networks is to use port mirroring (called "SPAN", for Switched Port Analyzer, by vendors such as Cisco, and given other names, such MLXe telemetry by Brocade Communications and other vendors)(also known as MIRROR port) or a monitoring protocol such as TZSP on routers and switches. This is a low-cost alternative to network taps and solves many of the same problems. However, not all routers and switches support port mirroring, and, on those that do, using port mirroring can affect the performance of the router or switch. These technologies may also be subject to the problem with full-duplex described elsewhere in this article, and there are often limits for the router or switch on how many pass-through sessions can be monitored, or how many monitor ports (generally two) can monitor a given session. Often, when the SPAN port is overloaded, packets will be dropped before reaching the monitoring device. There is also the possibility of losing some of the error packets that may be causing problems. If this data is not sent to the monitoring device because it is dropped, it is impossible to troubleshoot, no matter how advanced a device that may be used. Promiscuous sniffer This