Understanding the network.pdf - Back to Home

Dynamic routing might not be required to manage your network. However, a solid
understanding of the "hows" and "whys" prove beneficial if you are planning to have
any involvement with the Internet.
• Document your network before you set it up, and after it is up and running,
document any changes or special conditions (such as static routes on hosts)
that could cause problems if changes to the network occur.
• Keep your subnetting rules straight. With classful addressing, subnetting can
be used as long as the same mask is used for the entire address space.
Disconnecting classful subnets with other address spaces should be avoided,
but it is allowed. You can use VLSM to subnet classful subnets if your router
supports it. VLSM only affects routing; hosts do not require any modification
to operate on networks that use VLSM.
• Document your IP address subnetting. If you use VSLM to subnet address
spaces, be sure to map out the address tables before you use them. A poorly
thought-out VLSM strategy can create problems that will cause your network
to perform badly at the very least, and not at all at the very worst. Make sure
you use a dynamic routing protocol that supports VSLM if you decide to use
VLSM to partition your network address space.
ICMP
Internet Control Message Protocol (ICMP) is the IP error reporting messaging
service. ICMP is used to send error reports to the datagram sender from the receiver
or transit point (router) to indicate some kind of problem. One problem could be that
the destination host or service is unavailable or that the network is down. If you
have ever tried to Telnet or FTP to a host and were told that the "service was
unavailable" or "host not found," you have received an ICMP message.
Because IP is a connectionless transport, the sender is unaware if the destination
host and service are even available when it starts to send IP datagrams. Many
things can fail along the datagram's transit path, so ICMP is needed to report
failures when they arise.
ICMP's most visible manifestation is in the testing of host availability with Packet
Internet Groper Application (PING). PING enables IP connected hosts to send IP
datagrams of various sizes to destination hosts to test their reachability. Depending
on the implementation, PING can tell you simply if the host is just reachable, or it
can tell you how many packets were delivered and lost and what the traveling time
was for each packet from source to destination. Although all TCP/IP
implementations are required to provide support for ICMP, not all implementations
provide the tools. ICMP, though a part of the IP protocol (Layer 3), operates as a