clueless: ICMP is a security risk.
cluefull: ICMP is a mandatory compoment of the TCP/IP (that is the protocol stack of the Internet). It is required for TCP to work correctly. It is required for UDP to work correctly. It required for a couple of other famous transport layer protocols to work correctly. see here

clueless: You can't use the first and last subnets.
cluefull: You can use each and every subnet. You can also make subnets of different sizes. You can make supernets out of a bunch of classfull networks. It's called CIDR. It's been around for 10 year. Where have you been? More here and here

clueless: Classless routing is a security risk.
cluefull: Bullshit. Classless routing is mandatory part of the internet routing architecture as of Sep 1993. See here

clueless: You need all 8 wires to run a full-duplex 100BASE-TX connection
cluefull: Bzzeet. Wrong answer. You need the same 4 wires as with half duplex - pins 1,2,3,6 on the RJ-45 connector. more here

clueless: To connect two Ethernet 100BASE-TX cards or two hubs or two switches, or a hub to a switch to one another you need to make a rolled cable. That is on one end pins from left to right, on the other pins from right to left.
cluefull: No. A rolled cable will never work. First of all your cards or hubs or switches may support "Auto MDI-X", so a straight cable may work right away. If they don't you have to make a crossed cable. That is on one end [ wor, or, wgr, bl, wbl, gr, wbr, br ] and [ wgr, gr, wor, bl, wbl, or, wbr, br ] on the other. More here