OSI Reference / Network Protocols
|
||
Presentation -The presentation layer provides a variety of coding and conversion functions that are applied to application layer data. These functions ensure that information sent from the application layer of one system will be readable by the application layer of another system. Examples of presentation layer coding and conversion schemes include ASCII, EBCDIC, JPEG, GIF, TIFF, MPEG, QuickTime, various encryption methods, and other similar coding formats. | ||
Session -The session layer establishes, manages, maintains, and terminates communication sessions between applications. Communication sessions consist of service requests and service responses that occur between applications located in different network devices. Some examples of session layer implementations include Remote Procedure Call (RPC), Zone Information Protocol (ZIP), and Session Control Protocol (SCP). | ||
Transport - The transport layer segments and reassembles data into data streams. It is also responsible for both reliable and unreliable end-to-end data transmission. Transport layer functions typically include flow control, multiplexing, virtual circuit management, and error checking and recovery. Some examples of transport layer implementations include Transmission Control Protocol (TCP), Name Binding Protocol (NBP), and OSI transport protocols. | ||
Network -The network layer uses logical addressing to provide routing and related functions that allow multiple data links to be combined into an internetwork. The network layer supports both connection-oriented and connectionless service from higher-layer protocols. Network layer protocols are typically routing protocols. However, other types of protocols, such as the Internet Protocol (IP), are implemented at the network layer as well. Routers reside here at the network layer. Some common routing protocols include Border Gateway Protocol (BGP), Open Shortest Path First (OSPF), and Routing Information Protocol (RIP). Packets and datagrams are sent across this layer of the OSI model. | ||
Data Link
- The data link layer provides reliable transmission of data across a
physical medium. The data link layer specifies different network and
protocol characteristics, including physical addressing, network
topology, error notification, sequencing of frames, and flow control.
The Data link layer is composed of two sublayers known as the Media
Access Control (MAC) Layer and the Logical Link Control (LLC) layer. This can be seen in the following diagram: The LLC sublayer manages communications between devices over a single link of a network. LLC supports both connectionless and connection-oriented services used by higher-layer protocols. The MAC sublayer manages protocol access to the physical network medium. The IEEE MAC specification defines MAC addresses, which allow multiple devices to uniquely identify one another at the data link layer. Data link layer implementations can be categorized as either LAN or WAN specifications. The most common LAN data link layer implementations include Ethernet/IEEE 802.3, Fast Ethernet, FDDI, and Token Ring/IEEE 802.5. The most common WAN data link layer implementations include Frame Relay, Link Access Procedure, Balanced (LAPB), Synchronous Data Link Control (SDLC), Point-to-Point Protocol (PPP), and SMDS Interface Protocol (SIP). |
||
Physical
- The physical layer defines the electrical, mechanical, procedural,
and functional specifications for activating, maintaining, and
deactivating the physical link between communicating network systems. Physical layer specifications define such characteristics as voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, and the physical connectors to be used. Physical layer implementations can be categorized as either LAN or WAN specifications. Some common LAN physical layer implementations include Ethernet/IEEE 802.3, Fast Ethernet, FDDI, and Token Ring/IEEE 802.5.Some common WAN physical layer implementations include High-Speed Serial Interface (HSSI), SMDS Interface Protocol (SIP), and X.21bis. |
Steps of Data Encapsulation:
1. User information is converted to data
2. Data converted to segments
3. Segments converted to packets or datagrams
4. Packets and datagrams are converted to frames
5. Frames are converted to bits
Data link addresses: Physical address. Flat addressing scheme, physical address burned into network card (MAC address)
Network address: Logical address. IP or IPX - hierarchical scheme, assigned to a machine manually or dynamically.
IP Address Classes:
Class A | Net.Node.Node.Node | 0 | 1 - 127 | 127 networks, 16M nodes |
Class B | Net.Net.Node.Node | 10 | 128 - 191 | 16K networks 65K nodes |
Class C | Net.Net.Net.Node | 110 | 192-223 | 2M networks 254 nodes |
Subnetting Formulas: (count the bits only from the Node portion of the address. Therefore, for a Class B address, the total masked bits + unmasked bits = 16):
Max # of Subnets: 2(masked bits)-2
Max # of Hosts (per subnet): 2(unmasked bits)-2
IPX
To turn on:
ipx routing
Then, on interface:
ipx network {#} encapsulation {sap, arpa, snap, hdlc, novell-ether} {sec}
ipx network 3100 encapsulation sap sec
To monitor:
sh ipx traffic
sh ipx int e0
Frame Types:
802.3 - novell-ether - default
802.2 - sap
Ethernet_II - arpa
Ethernet_snap - snap
LAN Switching
All nodes on an ethernet network can transmit at the same time, so the more nodes you have the greater the possibility of collisions happening, which can slow the network down.
LAN Segmentation: breaking up the collision domains by decreasing the number of workstations per segment.
FastEthernet (100bt) - provides 10 times the bandwidth of older 10bastT Ethernet. Must have Cat5 cable, no longer than 100 meters, and FastEthernet NIC's and Hubs/Switches
Full-Duplex Ethernet - can provide double the bandwidth of traditional ethernet, but requires a single workstation on a single switch port, and NIC must support it. Collision free because there are separate send and receive wires, and only one workstation is on the segment. Half-Duplex must provide for collision detection, therefore can only use 50% of bandwidth available
Bridges - examines MAC address, and forwards frames unless the address was local. Forwards to all other segments it is attached to. Forwards multicast packets, so broadcast storms can occur.
Routers - examines network address, and forwards using the best available route to destination network. Can have multiple active paths.
Switching - examines MAC address. Same as multiport bridge.
Store-and-Forward - copies entire frame into buffer, checks for CRC errors. Higher latency. Used by Catalyst 5000 switches
Cut-Through - reads only the destination address into buffer, and forwards immediately. Low latency
Spanning-Tree Protocol (STP) IEEE 802.1d. - developed to prevent routing loops. STA (Spanning-Tree Algorithm) is implemented by STP to calculate a loop-free network topology. In Catalyst 5000 network, BPDUs are send and received by all switches, and processed to determine the spanning-tree topology.
Virtual LAN's - have different ports on a switch be parts of different subnetworks. Some benefits: Simplify moves, adds, changes. Reduce adminstrative costs, better control of broadcosts, tighten security, distribute load. Relocate server into secured locations.
IOS / Routing / Network Security
User Mode - ordinary tasks - checking status, etc. Need password depending on how you're entering (Virtual Terminal pw for telnet session, Auxiliary pw for aux port, Console pw for console port) conf t line vty 0 {line aux 0} {line con 0} login password letmein Privileged Mode conf t enable password letmein Banner: conf t banner motd # Hostname: conf t hostname MyRouter Editing: CTRL+A - beginning of line CTRL+E - end of line show history TAB completes command Help: Press ? after any command for a list of what comes next Router Elements/Configuration: show startup-config show running-config copy running-conifg startup-config erase startup-config setup reload boot system {flash / tftp} copy flash tftp copy tftp flash copy run tftp copy tftp run show proc show mem show buff show flash show cdp Routing Protocols Interior (within an autonomous system - AS - group of routers under the same administrative authority) RIP - 15 hop count max IGRP - 255 hop count max, uses reliability factor (255 optimal), and bandwidth OSPF - decisions based on cost of route (metric limit of 65,535) EIGRP - hybrid protocol, Cisco proprietary Exterior
Manual Routing: ip route {destination network} {mask} {port, on remote side, to get there} ip route 172.16.10.0 255.255.255.0 172.16.40.1 Dynamic Routing router rip network 172.16.0.0 router igrp {autonomous system #} network 172.16.0.0 sh ip route {rip / igrp}
Network Security / Access Lists Standard IP access list: access-list {number} {permit / deny} {source address} access-list 10 permit 172.16.30.2 Extended IP access list: access-list {number} {permit / deny} {protocol} {source} {destination} {port} access-list 110 permit tcp host 172.16.50.2 host 172.16.10.2 eq 8080 Wildcard masks - use masks to identify insignificant bits, eg access-list 11 permit 172.16.30.0 0.0.0.255 (permits anybody with 172.16.30.x) note: you can use 0.0.0.0 as the mask to limit to that specific host, or perfix it with ‘host' Applying the list to an interface (use access-group on the interface): int e0 ip access-group 110 out IPX Access lists: Standard: access-list {number} {permit/deny} {source} {destination} Extended: access-list {number} {permit/deny} {protocol} {source} {socket} {destination} {socket} access-list 810 permit 30 10 int e0 ipx access-group 810 out IPX SAP Filters: access-list {number} {permit/deny} {source} {service type} To apply - on interface: ixp input-sap-filter {number} access-list 1010 permit 11.0000.0000.0001 0 int e0 ipx input-sap-filter 1010 Access list Numbers allowed:
To Monitor Access Lists: Show access-list
WAN Protocols SDLC - developed by IBM in 70's - Data link layer protocol that transports SNA over WAN's HDLC - modified sdlc by ISO, default on Cisco routers X.25 - Sessions - DTE to DTE communication Full duplex, uses virtual circuits (PVC and SVC) Protocol Suite maps to Physical through Network PPP - runs on async (dial-up) or sync (ISDN) lines. Supports multi-protocols. Uses PAP or CHAP authentication. Int s0, encapsulation PPP Frame Relay - shared bandwidth over public network. Virtual circuits are identified by DLCI's. (Data Link Connection identifiers). LMI, co-developed in 1990 by Cisco, provides message information about current DLCI values (global or local significance), and the status of virtual circutis. Subinterfaces allow you to have multiple virtual circutis on a single serial interface. You must map an IP device to the DLCI (using the frame-relay map command or the inverse-arp function) int s0 encapsulation frame-relay {ietf} note: if you don's specify ietf, it uses cisco by default frame-relay interface-dlci {#} frame-relay lmi-type {cisco, ansi, q933a} Subinterfaces: int s0.x {multipoint / point-to-point} Mapping: int s0 inverse-arp or frame-relay map ip x.x.x.x # Monitoring: show frame {pvc / ip / lmi / traffic / etc.} ISDN - digital service that runs over existing telephone networks Normally used to support applications requiring high-speed voice, video, and data communications for home users, remote offices, etc. ISDN Terminal equipment types: TE1 - understand ISDN standards TE2 - predate ISDN standards, require a TA (terminal adaptor) Reference Points describe the point between: R - non-ISDN and TA S - user terminals and NT2 T - NT1 and NT2 devices U - NT1 and line termination ISDN Protocols: E - on existing telephone network I - concepts, terminology, and services Q - switching and signaling ISDN BRI: 2 64K B channels, plus 1 16K D channel ISDN PRI: Configuration example: config t isdn switch-type basic-dms100 int bri0 encap ppp isdn spid1 775154572 isdn spid2 455145664 |