CCNA Notes : Cont...
29. Routers can make alternate route decisions based on ICMP
messages, if appropriate. Routers send an ICMP message if the
destination is unreachable.
30. Port numbers are used by TCP/ UDP to set up sessions with other
hosts. The following are the recommended port numbers:
1.
Numbers 0 - 255 are used for public applications.
2.
Numbers 255 - 1023 are assigned to companies so that they can use
these port numbers in their applications.
3.
Numbers above 1023 are used by upper layers to set up sessions with
other hosts and by TCP to use as source and destination addresses.
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