What is sniffing|sniffers?

Sniffing is the simple process in which the network interface card is used to receive and monitor data that is not intended for that machine.The device or software that does sniffing are known as sniffer or more simply a network analyzer.Sniffing programs are very useful in gathering sensitive information like telnet username and password,ftp username and password.,credit card numbers,bank account details..and so on.Hence sniffing techniques are widely used by the attackers and hackers to monitor the key information that the hacker is interested in.In a network all the NIC(Network Interface card) have the unique mac(Media Access Control) address.In general the NIC responds to that packets only which contains its own mac address in the frames destination field or the broadcast address in the destination field.Network Interface cards also supports a mode known as promiscuous mode,in which it can receive all data packets and traffic that travels across the network.In promiscuous mode NIC generates a hardware interrupt to the CPU every packet’s frame they encounter(instead of the only the frames having the mac address or broadcast address)s.So the sniffer puts the NIC in to the promiscuous mode and capture/monitor the data packets traveling around the network by passing the all traffic to the operating systems TCP/IP stack.Hence a sniffer or network analyzer is also helpful in troubleshooting the networks and used by the network administrators.

Why sniffing threatens network security?

The sensitive information that can be collected by sniffers are :
1. Passwords(eg.ftp,telnet,pop,imap.. loging password)
2. Bank account numbers
3. Any other Private data
4. Low level Protocol Information

Some common Sniffing softwares(sniffers)

* dsniff
* Esniff.c
* TCPDump
* sniffit

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