1. ip transport was designed for heterogeneous networks

   1. networks using sna, x.25, ipx, xerox don't understand ip - addressing, framing, semantics

   2. how to make ip play well with others

   3. the cuckoo bird's strategy - make your packets look like theirs

   4. the ol' switcharoo - now people want to tunnel other protocols through ip - pvn

2. encapsulation

   1. one layer's packet is another layer's payload - usually higher and lower layers, respectively

   2. an encapsulated packet stream inherits the characteristics of the encapsulating stream - overhead, true, but also reliability, security, multicast and so on

3. tunneling vs encapsulation

   1. tunneling is policy, encapsulation is mechanism - other mechanisms include covert channels

   2. tunneling and encapsulation are both mechanisms - tunneling above the network layer and encapsulation below the transport layer

   3. i don't know why the difference is important

4. tunneling at any layer

   1. implementing ip in user space - over appletalk or e-mail

   2. implementing ip at the link layer - slip (rfc 1055) or ppp (rfc 1661)

5. examples

   1. private virtual networks - tunneling encrypted packets through ip

   2. moving ppp into the network - pptp rfc 2637, l2f, l2tp rfc 2661

   3. tunneling vs firewalls

      1. ip over dns

      2. lots and lots over http

      3. encrypted ip over udp, tcp

      4. http, tcp over e-mail

6. why is this important to clients and servers

   1. some rely on client-server architectures - pptp, ipsec

   2. an implementation technique for clients and servers

      1. more at middleware implementations, but an escape mechanism anyway

This page last modified on 10 April 2001.