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Cisco Certifiate Network Association
OSI Refrence / Network Protocols
Application – The application layer provides services directly to applications. The functions of the application layer can include identifying communication partners, determining resource availability, and synchronizing communication . Some examples of application layer implementations include TCP/IP and OSI applications such as Telnet, FTP, and SMTP, File Transfer, Access, and Management (FTAM), Virtual Terminal Protocol (VTP), and Common Management Information Protocol (CMIP). 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 (SPX). 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 (IPX). 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. 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. Steps of Data Encapsulation:
Data link addresses: Physical address. Flat addressing scheme where the physical address is burned into a network card (MAC address) Network address: Logical address. IP or IPX – hierarchical scheme. The address is assigned to a machine manually or dynamically. Physical through Transport layers are the Data Flow Layers Session through Application layers are the “Application” (Upper) Layers Hubs work on the Physical layer (Layer 1 device) Switches and Bridges work on the Data Link Layer (Layer 2 device) Routers work on the Network layer (Layer 3 device) Network Structure Defined by Hierarchy: Core Layer = Multi-layer switch Purpose is to switch traffic as fast as possible Characteristics:
Distribution Layer = Routers Primary function: perform potentially “expensive” packet manipulations such as routing, filtering, and WAN access. Characteristics include:
Access Layer = Switches and Routers End station entry point to the network IPX To turn on:
Then, on interface:
To monitor:
Frame Types: 802.3 – novell-ether – default 802.2 – sap Ethernet_II – arpa Ethernet_snap – snap LAN SwitchingSwitching – examines MAC address. Same as multiport bridge Three Switch Functions:
Address Learning: maintains MAC address table used to track the location of devices connected to the switch. Forward/filter decision: when a frame arrives with a known destination address, it is forwarded only on the specific port connected to that station.
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. This can slow the network down. Redundant Topology – eliminates single points of failure. Causes broadcast storms, multiple frame copies, and MAC address table instability problems. Multiple Frame Copies – when a new switch is added, the other switches may not have learned its correct MAC address. The host may send a unicast frame to the new switch. The frame is sent through several paths at the same time. The new switch will receive several copies of the frame. This causes MAC Database Instability. MAC Database Instability – results when multiple copies of a frame arrive on different ports of a switch. Multiple Loop Problems – complex topology can cause multiple loops to occur. Layer 2 has no mechanism to stop the loop. This is the main reason for Spanning – Tree Protocol. 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 most switches, BPDUs (Configuration Bridge Protocol Data Unit), are sent and received by all switches, and processed to determine the spanning-tree topology. (STP is on by default). A port is in either a forwarding or blocking state. Forwarding ports provide the lowest cost path to the root bridge. All ports start in the blocking state to prevent bridge loops. The port stays in a blocked state if the spanning tree determines that there is another path to the root bridge that has a better cost. Blocking ports can still receive BPDUs.
Time to Convergence – the time for all the switches and bridges ports transition to either the forwarding or blocking state. When network topology changes, switches and bridges must re-compute the Spanning-Tree Protocol, which disrupts traffic. Bridging Compared to LAN Switching –
Transmitting Frames through a Switch –
LAN Segmentation: breaking up the collision domains by decreasing the number of workstations per segment. Fast Ethernet (100bt) – provides 10 times the bandwidth of older 10bastT Ethernet. Must have Cat5 cable, no longer than 100 meters, and Fast Ethernet NIC’s and Hubs/Switches. 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. Virtual LAN’s – sets different ports on a switch to be part of different sub-networks. Some benefits: simplify moves, adds, changes; reduce administrative costs; have better control of broadcasts; tighten security; and distribute load. Relocate the server into a secured location. TCP/IP LayersApplication Layer: File transfer, E-Mail, Remote Login, Network Management, Name Management. Transport Layer: TCP (connection oriented), UDP (Connectionless).
Internet Layer – Corresponds with OSI Network layer
IP Address Classes: 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 RoutingRouters must learn destinations that are not directly connected. Static (manual): Uses a route that the network administrator enters manually. (Must be setup bi-directional)
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: Uses a route that a network routing protocol adjusts automatically router rip network 172.16.0.0 router igrp {autonomous system #} network 172.16.0.0 < use monitor, To>sh ip route {rip / igrp) Routing ProtocolsInterior (within an autonomous system – AS – group of routers under the same administrative authority)
Exterior
Counting to Infinity
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< to OR server) tftp software IOS (backup> <>copy tftp flash copy run tftp < configuration to tftp OR server) (backup> copy tftp run <>show proc show mem show buff show flash show cdp Network Security / Access ListsStandard IP access list:
Extended IP access list:
Access lists may be applied to:
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 prefix it with ‘host’ Applying the list to an interface (use access-group on the interface):
IPX Access lists:
IPX SAP Filters:
Access list Numbers allowed: To Monitor Access Lists:
WANLayer 1 Connection Types:Leased Lines – “point-to-point” or “dedicated connection”. Pre-established WAN path from customer through ISP to remote network. Circuit Switching – Dedicated circuit path must exist between sender and receiver for the duration of the “call.” Used with ISDN. Used when customer doesn’t need a 24/7 connection, but needs a reliable connection Packet Switching – Network devices share a
single point-to-point link to transport packets from a source to a
destination across a carrier network. They use virtual circuits that
provide end-to-end connectivity.
Customer premises equipment (CPE) - Devices physically located at subscriber’s location. Demarcation (or demarc) - The place where the CPE ends and the local loop portion of the service begins. (Usually in the “phone closet”). Local loop - Cabling from the demarc into the WAN service provider’s central office. Central Office switch (CO) - Switching facility that provides the nearest point of presence for the provider’s WAN service. Toll network – The switches and facilities,
(trunks), inside the WAN provider’s “cloud.”
High-Level Data Link Control (HDLC) – Default encapsulation type on point-to-point, dedicated links, and circuit switched connections. Used for communications between two Cisco devices. Point-to-Point Protocol (PPP) – Provides router-to-router and host-to-network connections over synchronous and asynchronous circuits. Uses PAP or CHAP authentication. Int s0, encapsulation PPP Serial Line Internet Protocol (SLIP) – Standard protocol for use with TCP/IP. It has, for the most part, been replaced by PPP. X.25/Link Access Procedure, Balanced (LAPB) - Standard that defines how connections between DTE and DCE are maintained. Frame Relay – Industry standard, switched data link layer protocol that handles multiple virtual circuits. (Replaces X.25). Shared bandwidth over public network. Virtual circuits are identified by DLCI’s. DLCI - (Data Link Connection identifiers). LMI (Local Management Interface), co-developed in 1990 by Cisco, provides message information about current DLCI values (global or local significance), and the status of virtual circuits. Subinterfaces allow you to have multiple virtual circuits 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)
Asynchronous Transfer Mode (ATM) –
International standard for cell relay while using multiple services
(voice, video, data)
Uses the Data Link and Physical Layer of OSI model.
ISDNISDN - 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:
Reference Points describe the point between:
ISDN Protocols:
ISDN BRI (Basic Rate Interface): 2 64K B channels, plus 1 16K D channel ISDN PRI (Primary Rate Interface): Configuration example: config t isdn switch-type basic-dms100 int bri0 encap ppp isdn spid1 775154572 isdn spid1 455145664
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