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Network Security Hacks by Andrew Lockhart

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Detect ARP Spoofing

Find out if there’s a “man in the middle” impersonating your server.

One of the biggest threats to a computer network is a rogue system pretending to be a trusted host. Once someone has successfully impersonated another host, they can do a number of nefarious things. For example, they can intercept and log traffic destined for the real host, or lay in wait for clients to connect and begin sending the rogue host confidential information. Spoofing a host has especially severe consequences in IP networks, as this opens many other avenues of attack. One technique for spoofing a host on an IP network is Address Resolution Protocol (ARP) spoofing. ARP spoofing is limited only to local segments and works by exploiting the way IP addresses are translated to hardware Ethernet addresses.

When an IP datagram is sent from one host to another on the same physical segment, the IP address of the destination host must be translated into a MAC address. This is the hardware address of the Ethernet card that is physically connected to the network. To accomplish this, the Address Resolution Protocol is used.

When a host needs to know another host’s Ethernet address, it sends out a broadcast frame that looks like this:

01:20:14.833350 arp who-has 192.168.0.66 tell 192.168.0.62

This is called an ARP request. Since this is sent to the broadcast address, all Ethernet devices on the local segment should see the request. The machine that matches the requests responds by sending an ARP reply ...

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