here’s the day 1 notes. I was going to make omnigraffle diagrams of the diagrams I drew by hand, but that would just be too time consuming; instead I’ll just scan them in when I return.
Day 1 - 4/29 Chapter 1 Basic Concepts 1) Routers create broadcast domains, switches do not. Broadcast packets will be sent to all ports on a switch (without VLANs), but routers will never forward broadcast packets between networks. 2) Routers make dissimiliar networks talk to each other. Default gateway for a host is always a router Cisco's three layer model for networks: Access Layer = End users, workstations, switches, etc Distribution Layer = Filtering, routing, WAN access; creates broadcast domains Core Layer = where major services or servers exist OSI Reference Model: - a way to understand how an internetwork operates - guidline for creation or implemenation of standards, devices and networking schemes - breaks down a complex system into simpler elements - allows for specialized design and development of modular components Application Layer: - User interaction - Applications exist here (Word, FTP client, etc) Presentation Layer: - converts data into a specific format - ensures that data can be read from the application layer of one system to the application layer of another system - jpeg, gif, .doc, encryption Session Layer: - Establish, manage, terminate communications - system calls, process management - eg database server & client Transport Layer: - Responsible for end to end transport - connection oriented (TCP) or connectionless (UDP) - Port assignments - After adding TCP header, unit is known as a SEGMENT - Applications determine which transport protocol is used TCP = reliability, data will be acknowledged UDP = unreliable, no acknowledgement Transport layer adds TCP or UDP headers Within that header there are logical ports; source port and destination port. The destination port is used to differentiate between applications. Even if source IP, dest IP, source MAC and dest MAC are the same, the communications between different applications on the two hosts is identified by the TCP or UDP port number. Source port is random; destination port is well known (and less than 1024) Names for data units are associated with specific layers: Transport --> Segment Network --> Packet Data Link --> Frame Physical --> Bits PDU = protocol data unit. PDUs are added as info travels down the stack and removed as it travels up the stack. PDUs are refered to as headers or trailers. Encapsulation is the process of adding PDUs, de- encapsulation removes PDUs. Collision Domains / Broadcast Domains: Collision Domains: - Signaling - Ethernet must have rules / standards to communication - Allows access to one user at a time - Corrects collisions Definitions: Collision domain: devices attached to the same physical media such that if two devices access the media at the same time, a collision occurs (eg hub). Broadcast domain: a group of devices in a network that receive each others broadcasts On a switch, each port is its own collision domain. CSMA / CD = carrier sense multiple access / collision detect: - Each host listens on teh line for traffic - If in use, back off using algorithm - If not in use, send traffic - If traffic is not heard on teh line, assume collision and resend; back off algorithm - If traffic is heard, assume success. If two sets of hosts within a collision domain try to use the media at the same time, a collision occurs. Using CSMA, hosts sense the network to know when to talk. Back off algorithm - wait to send; round robin style. Problems with CSMA / CD: more hosts = more collisions Solution = create more collision domains (replace hubs with switches) Half duplex = send OR receive; uses CSMA / CD Full duples = send AND receive; does not use CSMA / CD Data Link Layer 2 sublayers: - MAC = 802.3; physical addressing - Logical Link Control - LLC 802.2 - Identify different protocols with SAP / SNAP and then encapsulate them in order MAC: 48 bits in a MAC address = hardware address or NIC address LLC: uses either SAP or SNAP to differentiate between protocols; eg IP, IPX, AppleTalk. SAP = service access point SNAP = subnetwork access protocol Frames: Preamble is a combination of 1s and 0s that signify the start of a frame Preamble Dest MAC Source MAC Type Data CRC 64 bits 48 bits 48 bits 16 bits MTU 1500 32 bits Data portion of a SAP frame: Dest SAP Src SAP CNTL DATA DSAP / SSAP = 1 byte Pointer to upper layer protocols 06 hex = IP EO hex = IPX In SAP, your DSAP and SSAP tells dest and source protocol Data portion of a SNAP frame: DSAP SSAP CNTL OUI Type Data AA AA 03 ID DSAP and SSAP fields have a fixed value of AA in SNAP frames. CNTL is always 03. OUI is a vendor code. Type field contains an EtherType which determines protocol. Bridges and Switches - Operate at layer 2, the data link layer - Switching is *hardware* based frame forwarding - ASIC = application specific integrated circuits; used to create high performance chips - Fast; scales up to gigabit speeds - Bridge = 2 or 4 ports - Software based; slower Bridges can be used to increase the number of collision domains, which decreases the number of collisions. Bridging / Switching Process: - Receives frame - Checks forwarding table for the dest MAC address - Proceeds with one of three functions: - Filter data = when source and dest are on same physical port - Floods data = sends to all ports; when dest port is unknown - Copies the frame to another segment = from one physical port to another Network Layer: - Defines how to transport traffic to devices not locally attached; not in same broadcast domain - 2 pieces of information required: logical address of destination path to reach destination IP address = 32 bits; exists in network layer Routers have information from all lower layers (due to encapsulation) IP addresses are assigned to interfaces of routers. Subnet mask determins which portion of IP is the network portion and which is the host portion. Router interfaces must be on different networks Once you configure IP addresses on router interfaces, the routing table will look like this (see diagram) Define static routes = manual routing entries Enable Routing protocols = routers talk to each other and exchange routing tables Router functions: - Does not forward layer 2 broadcasts / multicasts - Determines optimal path to destination - strips layer 2, forwards on layer 3 addresses - ARP - can filter traffic; access lists multicast = specific group of hosts broadcast = everybody unicast = just one host ARP = Address Resolution Protocol; when you have IP and need MAC. (see diagram) MAC addresses are replaced to allow for return communication without flooding. - Can perform both bridging and routing - Can provide connectivity between VLANs in switched environment - Can provide quality services based on traffic type Uses bridging to pass non routable protocols. If VLANs want to talk to each other, they need a router. Chapter 2 UTP Implementation 3 kinds of UTP: - straight through; used to connect PC to router, hub, or switch; dissimiliar OSI layers - crossover; switch to switch, hub to hub, etc; used to connect devices on same layer - rollover; used for console ports; DB9 connector (com1 on a pc) console port = in band (local) AUX = out band management (modem dialup) WAN Connections (diagram) CSU / DSU; analog to digital and back; makes signaling at both ends compatible Supported by Cisco Equipment: EIA / TIA - 232 EIA / TIA - 449 V.35 X.21 EIA - 530 Needed on serial links: DCE = modem = gives clock rate to router = data communications equipment DTE = accepts clock rate = data terminal equipment When connecting routers to each other, one end must be made to be a DCE (DTE by default) Serial Interfaces on a router: - Abbreviated differently on different routers - s0 = fixed - s0/0 = modular Router commands: erase start = deletes startup config from NVRAM reload = reboot router; return to factory defaults NVRAM RAM startup config running config prompts: > = user mode # = privledged mode show ip interface brief = brief listing of interfaces & their status Interfaces are administratively down on Cisco routers by default Chapter 3 Router Startup Processs: 1) Power On Self Test (POST); finds / checks hardware 2) Run startup routines; locate / load IOS (Internet Operating System) 3) Locate / load software config file Config locations: - console terminal or AUX - CDROM - TFTP connected via ethernet (can hold configurations and IOS backups) Console Help: ? = list of commands s? = list commands that start with s show ? = commands used with show Abbreviating commands: show interfaces = sh int Error Messages of 3 different types: - Ambiguous command - more than one possible meaning (for an abbreviation) - incomcplete command - invalid input detected at ^ marker show history = history of commands entered control P = previous command in history buffer control N = next command in history buffer control a = beginning of line control e = end of line control f = forward one character control b = back one char control u = clear line control r = refresh command buffer show version = system information; IOS version, hardware info show running-config = running configuration show int serial0 = detailed info on interface show ip = for switches, not routers configure terminal = glocal configuration mode (show commands do not work in global config mode) enable = enter privledged mode disable = exit priv mode Setting IP on a switch: ip address x.x.x.x 255.0.0.0 - enables SNMP management setup - from exec mode to enter guided setup control-c exits setup process At the end of setup, there are three options: 0) go to exec without using or saving config that was just set up 1) restart setup 2) accept / save config, go to exec mode Routers only: no terminal editing = disbles terminal editing (control) commands terminal editing = enables editing commands Lines greater than 69 characters show a $ at beginning of line show startup-config = show startup config copy run start = saves running config to startup config in NVRAM from global config: int s0 = interface config for serial0 - prompt changes to: Router(config-if) sub-interfaces; multiple subinterfaces can be on a single physical interface int s0.1 = from global config; configures sub-interface 1 on s0 from priv mode: show line - cty = console - vty = virtual telnet sessions - aux = aux By default, Cisco routers have 5 VTY lines from global config: line console 0 = line config mode router rip = configure router to use RIP control-Z returns to priv mode (use from global config or interface config) setting the hostname: hostname
passwords: Setting a console password: config terminal line console 0 password login Setting a VTY password: configure terminal line VTY 0 4 password Setting an enable (priv mode) password: enable password Setting an encrypted enable password: enable secret - does not show with 'show running-config' To disable passwords, use the no form: no enable password To disable console timeouts: config t line console 0 exec-timeout 0 0 By default, logging is sent to console logging syncronyous = disable logging output to console while entering a command show ip route = shows routing table (diagram of pod 5) Configuring Interfaces (from interface config mode): address on port data encapsulation media type define bandwidth set direct memory access buffering parameters ip address = assign an IP to an interface no shut = removes "administratively down" status show controllers s0 = determine if serial 0 is dce or dte DCE ends must set clocking from interface config mode clock rate xxxxx Entering bandwidth: - Used by routing protocols to determine metric - By default, T1 speed Disabling Interfaces (serial0 for example): config t int s0 shut Chapter 4 CDP = Cisco Discovery Protocol Enabled by default Media and protocol independant Used to aid in managing Cisco devices Summary of neighbor info shows only info within a collision domain (directly attached) show cdp neighbors show cdp ? show cdp neighbors detail Disabling CDP globally: config t no cdp run Disabling CDP on an interface: config t int s0 no cdp enable Telnetting: telnet - cannot telnet out of catlyst 1900 control-shift-6, x = suspent telnet session show sessions = shows active sessions show users = shows connected users clear line = kick user resume = resume telnet session (can also just press enter if only one session) ping traceroute