-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Friday 05 December 2003 05:39, Joshua Banks wrote: > Hello, > > I thought for any type of IP packet to go out onto the internet Zone > (passed the local default gateway) that the packet needed to use either > TCP or UDP to accomplish transportation?
Layer 3: IP - The protocol used to transport arbitrary packest from one endpoint to another endpoint. The endpoints are specified as IP numbers. The internet is mainly built around this protocol, with all routers knowing how to reach any given IP. Most everything transported on the internet is some form of IP. ICMP - This is a protocol with many of the properties of a layer 4 protocol, but as it is an integral part of IP it is implemented as a layer 3. ICMP used the standard IP header, and includes an additional type field (e.g. "echo request" and "echo reply" used for ping) + data relevant to the icmp type. ICMP is sort of a helper protocol, with which machines with an IP can transmit information in between each other in order to notify of events or request changes in the way IP is treated. Layer 4: TCP - A protocol that adds "ports" to IP's endpoint definition, support for streams (packet order is consistent) and delivery-guarantees (you know whether a packet has reached its destination). This protocol is built on top of IP, and the IP part is used to transport data from ip to ip. UDP - A protocol that also adds "ports" to IP's endpoint definition. Again, this protocol uses the IP part for transportation in between machines, and when a packet reaches the machine an IP belongs to the ports are used to further route the packet to the correct application. A typical traceroute happens as follows: A wants to traceroute E. In between them you have B, C and D. A sends a UDP (yes UDP is what default traceroutes use) packet to E, with a TTL (Time To Live) value of 1. B receives this packet, and sees that it has travelled TTL machine-machine hops. It then drops the packet as the TTL is exceeded, and sends an icmp ttl-exceeded back to A, including a specification of which packet it dropped. A now resends the UDP packet, this time with a TTL of 2. The packet travels to C this time, and again a ttl-exceeded icmp is sent back. This continues until the UDP packet actually reaches E. While this happens, the traceroute application shows the IPs of the machines it receives ttl-exceeded ICMPs from, and you'll get a nice map of how traffic *from A to E* travels. You still can't know how traffic from E to A travels, as that can be a totally different path (async routing), although in many cases it is the same. As others mentioned, there are several layer 3 and layer 4 protocols besides these mentioned here. Google for "OSI Layer" and you'll find it. - --Erik -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.2 (GNU/Linux) iD8DBQE/0I3Mds9m9uhAobARAqu/AKCVV1DUA7Q9qeP1jrTFOA7Z4zn8vACgwZyi AUVj39Aj3KeOp7uKe3mqxSA= =VOr6 -----END PGP SIGNATURE----- -- [EMAIL PROTECTED] mailing list
