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The Book of PF, 2nd Edition by Peter N.M. Hansteen

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Making Your Network Troubleshooting Friendly

Making your network troubleshooting friendly is a potentially large subject. Generally, the debugging or troubleshooting friendliness of your TCP/IP network depends on how you treat the Internet protocol that was designed specifically with debugging in mind: ICMP.

ICMP is the protocol for sending and receiving control messages between hosts and gateways, mainly to provide feedback to a sender about any unusual or difficult conditions en route to the target host.

There is a lot of ICMP traffic, which usually happens in the background while you are surfing the Web, reading mail, or transferring files. Routers (you are aware that you are building one, right?) use ICMP to negotiate packet sizes and other ...

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