Network & Internet Layers: OSI Model
Physical
Repeaters (increase signal),
Hubs (connect devices),
Physical interface of NIC (1's and 0's in NIC connects with bits specifying address in a packet, allowing packet)
Modems (clock & data flow), DSU/CSU (clock & data flow)
(No control of collisions at this level!)
Data Link
ARP (IP to& MAC)
RARP, DCHP, BOOTP (MAC to IP)
(Collision Domain: the collisions in a collision domain are limited to devices on a single switch port or on one side of a bridge; do not cross!)
(Broadcasting continues across bridges and switch ports however)
Bridging takes place at the link layer (see http://osdir.com/ml/linux.newbie/2003-05/msg00198.html
MAC addressing (12 * 4 bit address)/MAC Address Table (resolves MAC address to port)
DLCI or Data Link Connection Identifier (used in frame relay to identify connection between frame relay switch and router)--configured by LAPF
Protocols at this Layer: Ethernet, PPPoE, PPP, HDLC, Frame Relay (PPPoE, PPP, & (I think) HDLC, use LCP packets; for more on these protocols see: http://www.petri.co.il/csc_3_wan_protocols_you_should_know.htm)
(NOTE: Ethernet is used on fast ethernet connections & such; PPPoE is used on DSL connections to Internet Service, PPP, hdlc, and frame relay are used on serial connections) Link Control Protocol (LCP) Packets (configure & test data link unit--for network control protocol):
* Maximum Receive Unit (MRU)
* Link Authentication (PAP, CHAP)
Network Control Protocol Packets (configure network layer protocol--such as ip)
Encapsulation of data at layer 2 makes what is called a frame! This encapsulation provides error checking--but no error recovery. The Frame includes: the header, followed by the packet from layer 3 (below), followed by the trailer.
Local Management Interface (used by frame relay to provide circuit diagnostics)
Network
(Used to address host from other subnets or networks; divides at network or subnet level; no broadcasting or multicasting across subnets or networks--only within; note that broadcasts and multicasts are limited to a particular VLAN if there are VLAN's assigned)
Routing takes place at the network layer (see http://osdir.com/ml/linux.newbie/2003-05/msg00198.html).
IP addressing; routing tables (can be configured/used by routing protocols--below)
Protocols at this Layer: Routing protocols (OSPF, RIP, RIP v2, EIGRP, BGP) (use IP or other protocol addressing)
VLANs use routers for routing to connect with other VLANs (& limit broadcasting of packets to a single VLAN)
Encapsulation of data at this layer makes what is called a packet. The packet includes a header, followed by the segment encapsulated at layer 4 (below).
Transport
This make the connections between the ports (the port the application layer--layer 7--will use)
The TCP handshake checks for and recovers from packet loss. (It can use data about errors in packets from previous layers I think)
Encapsulation of data at this layer makes what is called a segment. The segment includes a header plus the data from the application/layer 7 (see below).
Session, Presentation, & Application
The Session Layer keeps track of sessions.
The Presentation Layer deals with the formatting of data (ascii, ansi, utf-8, gif, jpg, & so forth).
The Application Layer is for applications like the browser, file transfer programs, email, and such.