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Compilation stack

Four Router Functions Packet switching, Packet filtering, Internetwork communication, Path selection
7 Layers of OSI Model Application, Presentation, Session, Transport, Network, Data Link, Physical
Application Layer User interface. File, print, message, database, and applications.
Presentation Layer Data encryption, compression, and TRANSLATION.
Session Layer Separates data of each application. Dialog control
Transport Layer Provides reliable or unreliable delivery, and performs error correction before retransmit. End-to-end control. Segments
Network Layer Logical addressing for use in path selection, ROUTING. Packets.
Data Link Layer Access to media via MAC address. Also performs error detection. Frames
Physical Layer Voltage, wire speed, and pinout of cables. Bits
Flow Control Ensure data integrity at the Transport layer. Segments delivered are ack'd back to the sender, retransmit not ack'd. Sequenced segments reconstructed.
Windowing The size of the window controls how much information is transferred from one end to the other before an ack is required.
Metric The distance to the remote network.
CSU Channel Service Unit
DSU Data Service Unit
DTE Data Terminal Equipment
DCE Data Communication Equipment
Collision Domain Where one device sends a frame out on a physical network segment forcing every other device on the same segment to pay attention to it.
Hub One collision domain. One broadcast domain. HALF DUPLEX
Switch One collision domain on each port. One broadcast domain by default, which can be changed with vlans.
CSMA/CD Carrier Sense Multiple Access with Collision Detection. Prevents devices from transmitting simultaneously on the same network medium.
Full Duplex Talking in both directions at the same time.
Half Duplex Talking in one direction at a time.
MAC Address 48 bits. 24 (6 characters) OUI number, 24 vendor specific.
Nibble Values 8 4 2 1
Byte Values 128 64 32 16 8 4 2 1
1 00000001
2 00000010
4 00000100
8 00001000
16 00010000
32 00100000
64 01000000
128 10000000
192 11000000
224 11100000
240 11110000
248 11111000
252 11111100
254 11111110
255 11111111
0 0000
1 0001
2 0010
3 0011
4 0100
5 0101
6 0110
7 0111
8 1000
9 1001
A, 10 1010
B, 11 1011
C, 12 1100
D, 13 1101
E, 14 1110
F, 15 1111
Frame Encapsulation Destination address, source address, data, FCS
802.3 10Base-T
802.3u 100Base-TX
802.3u 100Base-FX (fiber)
802.3z 1000Base-SX (multimode fiber)
802.3z 1000Base-LX (single-mode L = LONE fiber)
802.3.an 10GBase-T
Straight-through cable Host to switch or hub, router to switch or hub. Four wires used - 1, 2, 3, and 6
Crossover cable 1 - 3, 2 - 6
Rollover cable 1-8,2-7,3-6,4-5
Fiber optic cable Core, cladding, buffer
TCP Transmission Control Protocol. Takes large blocks of info from an app and breaks them into segments.
IP Internet Protocol
Telnet Uses TCP, sent in clear text
SSH Secure Shell. Uses TCP, encrypted
FTP File Transfer Protocol. A program operating as a protocol
TFTP Trivial File Transfer Protocol. Stripped down version of FTP.
SNMP Simple Network Management Protocol. Collects and manipulates network information from an NMS.
NMS Network Management Station.
HTTP Hypertext Transfer Protocol. The web server is found, then the page is requested, and the page information is sent back to the host.
NTP Network Time Protocol. Time is updated from an NTP server. THIS HELPS WITH TROUBLESHOOTING via a time stamp.
DNS Domain Name Service. Resolves host names/internet names to ip addresses.
DHCP Dynamic Host Control Protocol. Assigns ip addresses to hosts. DHCPDiscover, DHCPOffer, DHCPRequest, DHCPAck
APIPA Automatic Private IP Addressing. Host assigns itself then you're network is down.
UDP User Datagram Protocol. Thin protocol, faster than TCP, but less reliable.
ARP Address Resolution Protocol. Finds the hardware address of a host from a known ip address.
Bit One digit, a 1 or a 0.
Byte Typically 8 bits.
Octet 8 bits.
Network address The primary address of a network.
Broadcast address The address used to send info to all hosts in a network.
Class A Address 0 - 127
Class B Address 128 - 191
Class C Address 192 - 223
Address Class A -
Address Class B -
Address Class C -
Layer 2 Broadcast ff:ff:ff:ff:ff:ff
Loopback Address Can be any address -
VLSM Variable Length Subnet Mask. When your subnet mask does not match your typical address class (classless). example:
Summarization Allows routers to advertise many networks with one address.
User exec mode Limited to basic monitoring commands.
Privileged exec mode Provides access to all other router commands.
Global configuration mode Commands that affect the entire system.
Specific configuration modes Commands that affect interfaces/processes only.
Setup mode Interactive configuration dialog.
hostname (config)#hostname myrouter
banner motd Message you see when you log in.
Setting up SSH A domain name is required to configure this. (config)# ip domain-name mypage.int (config)# username admin password mypass (config)# crypto key generate rsa
Setting up SSH (more) (config)# ip ssh version 2 (config)# line vty 0 4 (config)# transport input ssh telnet
Service password-encryption Encrypts any passwords you configure after this is submitted.
How to enable an interface? no shutdown
Secondary ip address ip address secondary
Finding stuff show run | include 192.168.0 show run | begin access
Serial Interface The DCE end must be configured with a clock rate. (config)# clock rate 64000
Saving your changes to memory copy running-config startup-config
Deleting the startup config erase startup-config (then reload)
Clearing counters on an interface router#clear counters fa0/0
No buffer You don't have any buffer room left for incoming packets.
Ignored If packet buffers are full, packets will be dropped. Increments with no buffer.
Runts Frames that didn't meet the minimum frame size of 64 bytes. Typically caused by collisions.
Giants Frames larger than 1518 bytes.
Late collisions This increments with duplex mismatch.
Bootstrap stored in ROM. Boots the router up and loads the IOS.
POST Power-on self-test. stored in the ROM. Checks the basic functionality of the router hardware and determines which interfaces are present.
ROM monitor rommon. used for troubleshooting and loads when the IOS in flash fails to load.
RAM (cisco router) used to hold packet buffers, ARP cache, routing tables, and also the software and data structures that allow the router to function. Running-config is stored in RAM.
Flash Memory Stores the Cisco IOS by default. Flash memory is not erased when the router is reloaded.
NVRAM Nonvolatile RAM. used to hold the router and switch configuration. NVRAM IS NOT ERASED WHEN THE ROUTER OR SWITCH IS RELOADED.
Configuration register used to control how the router boots up. Default is 0x2102. 0x2142 resets the router
DHCP relay ip helper-address
show ip dhcp binding shows the status of any leased ip's to hosts
show ip dhcp pool *poolname* shows the range of ip's and stats of current ip leases.
show ip dhcp server statistics shows dhcp server stats
show ip dhcp conflict shows ip conflicts
syslog server logging host service timestamps log datetime ntp server version 4
CDP Cisco Discovery Protocol
show ntp status shows if the router is communicating with the ntp server.
show ntp associations shows the information about ntp.
show cdp neighbor detail shows a lot of details about neighboring devices.
LLDP Link Layer Discovery Protocol. IEEE version of CDP.
show ip route shows all the contents of the routing table.
Static routing Manually added routes
Default routing When a router only has one connection to other networks it is a stub router. All routes to go to the next hop address.
Dynamic routing When protocols are used to find networks and update routing tables.
AD Administrative Distance. The distance a router lists for a route in the routing table.
Connected Interface default AD 0
Static route default AD 1
EIGRP default AD 90
OSPF default AD 110
RIP default AD 120
External EIGRP default AD 170
Unknown default AD 255
Distance Vector routing Find the best path to a remote network based on distance.
Link State routing Find the best path to a remote network based on hop count. If a network is 16 hops away is is unreachable.
Passive Interface Preventing routing protocols from being sent out an interface that this is configured on.
Switch interface Any state other than up/up and it won't forward frames.
administratively down/down The interface is in shutdown.
down/down No cable plugged in, wrong cable pinouts, bad cable, the speeds are mismatched between devices.
up/down Check the other end, the interface may be misconfigured, shutdown, or the cable may not be seated properly.
down/down (err-disabled) Port security has disabled the interface
solid amber light The system has power, but is not functioning properly.
solid green light The system has power, but there's no current traffic.
flashing green light The link is up and passing traffic.
flashing amber light The port is blocked by spanning tree.
Serial connection 9600 baud, 8 data bits, 1 stop bits, parity none, flow control none.
OSPF version 3 Supports IPV6
ICMP version 6 Supports IPV6
NDP Neighbor Discovery Protocol. Works with IPV6
show mac address-table shows the vlans that each mac address is in and what interface they are connected to.
switchport security switchport mode access switchport port-security mac-address sticky switchport port-security maximum 2 (1 is default) switchport port-security violation shutdown
VLAN Virtual Local Area Network. int fa0/2 switchport mode access switchport access vlan 2
Three benefits of vlans Broadcast control Security Flexibility/Scalability
Voice vlan The only option for more than one vlan to be assigned to a port. Otherwise, only one vlan per port.
Trunk port A way to transport multiple vlans between switches. switchport trunk allowed vlan (all, 1-4)
802.1q IEEE method of frame tagging on a trunk port
ISL Inter-switch link. Proprietary to Cisco switches.
show vlan shows you all vlans, names, status, and ports.
show int trunk shows trunked ports, mode (on), encapsulation (802.1q), status (trunking), native vlan, and vlans allowed on each trunk port.
Inter-vlan routing int fa0/0.1 encapsulation dot1q 1 ip address int fa0/0.2 encapsulation dot1q 2 ip address
Standard access list Use only the source ip address as the condition test. 1-99, 1300-1999 access-list 10 permit line vty 0 4 access-class 10 in
Extended access list Test based on source ip, destination ip, protocol field, and/or port number. 100-199, 2000-2699 access-list 110 deny tcp host eq 80 access-list 110 permit ip any any
Named access list Can be standard or extended. ip access-list standard blockstudents (config-std-nacl)#deny (config-std-nacl)#permit any
Inbound access list Packets coming into the router are processed through the access lists before they can leave the router.
Outbound access list Packets are routed to the outbound interface and then processed through the access lists.
remarks (config-ext-nacl)#remark deny all students from faculty network
show access-list Displays all access lists and their settings
show access-list 110 Displays only the information for the list you selected, in this case access list 110.
show ip access-list shows only the ip access lists on the router.
NAT Network Address Translation
Static NAT One-to-one mapping of a private ip to/from a public ip. ip nat inside source static
Dynamic NAT Mapping of private ip's to/from a pool of public ip's. ip nat pool students
Overloading (NAT) Mapping of private ip's to/from a single public ip. (most common) ip nat pool students prefix-length 29 ip nat inside source list 7 pool students overload
Inside local Source host ip (private ip)
Outside local The address on the external interface of a router. Public ip
Inside global The address on the external interface of a router. Public ip
Outside global The address on the external interface of a router. Public ip
IPV6 128 bits, first 48 bits global prefix, 16 bits subnet, last 64 bits interface id. ipv6 address 2001:a9c:52d6:1::/64 eui-64
Global unicast addresses 2000::/3
0:0:0:0:0:0:0:0 ::.
0:0:0:0:0:0:0:1 ::1
0:0:0:0:0:0: Mixed ipv4 in ipv6 format
FC00::/7 Unique local unicast range
FE80::/10 Link-local unicast range
3FFF:FFFF::/32 Reserved for examples and documentation
2002::/16 Used with 6-to-4 tunneling
Root bridge The switch with the lowest bridge id.
Non-root bridge All switches that are not the root bridge.
BPDU Bridge Protocol Data Unit.
Bridge id The bridge id is how STP keeps track of all the switches in the network.
Port cost Port cost determines the best path when multiple links are used between switches. The cost of a link is determined by the bandwidth of a link.
Path cost Port costs on the way to the root bridge are added together to equal path cost.
Root port The port with the lowest path cost to the root bridge.
Designated port A port that has been found to have the lowest cost.
Non-designated port Has a higher cost than the designated port.
Forwarding port Forwards frames and is either a root port or designated port.
Blocked port Won't forward frames, but listens to BPDU frames from neighbor switches.
Listening port Listens to BPDU's to prevent loops before forwarding frames. Does not populate the MAC address table.
Learning port Listens to BPDU's. Populates the MAC address table.
Forwarding port Sends and receives all frames. If the port is still a designated or root port at the end of the learning state it will go into forwarding state.
Convergence When all the ports have transitioned to either blocking or forwarding states.
10Mbps cost 100
100Mbps cost 19
1000Mbps cost 4
10,000Mbps cost 2
IEEE 802.1d The original STP standard. CST - Common Spanning Tree
PVST+ PER VLAN SPANNING TREE PLUS. Cisco propriety enhancement for STP with a separate 802.1d instance for each vlan. Multiple root bridges possible.
IEEE 802.1w Rapid Spanning Tree Protocol. One root bridge.
Rapid PVST+ Cisco version of RSTP. Separate instance per vlan.
Spanning Tree Protocol Root bridge is chosen based on bridge, the lowest bridge id wins. If the bridge id ties then the lowest priority number wins. If priority ties then lowest port number wins.
Set STP Priority spanning-tree vlan 10 priority 4096 spanning-tree vlan 10 root primary
STP commands show spanning-tree summary show spanning-tree
PortFast Ports transition from blocking to forwarding immediately once the switch is turned on. Configured on a port for devices such as a server.
PortFast commands (config)#int range fa0/1 (config-if)#spanning-tree portfast
BPDU Guard Enable this on a port running portfast. If this port receives a BPDU the switch will place that port into error disabled (shutdown). Prevents a switch or hub from causing loops at access layer.
BPDU Guard commands (config)#spanning-tree portfast bpduguard default (sets this globally) (config-if)#spanning-tree bpduguard enable
EtherChannel A way to bundle up to 8-100Mbps ports or 2-1000Mbps ports.
EtherChannel configuration Configure trunking on the ports first. (config-if-range)#channel-group 1 mode active
Cisco licensing show license udi router#license install flash:FTX67897976.lic router#license save flash:your_license.lic
FHRP First Hop Redundancy Protocol. Using multiple routers to add redundancy by using a virtual ip and mac address for hosts to use as a gateway. One router as active and one as standby.
HSRP Hot Standby Router Protocol. Not load balancing. Virtual router as gateway. Active router, standby router, virtual router, and other routers that could be set as standby.
HSRP MAC address Includes 07.ac in the middle
HSRP timers Hello (3 seconds), hold (10 seconds), active (resets when hello arrives), and standby (resets when hello arrives.
HSRP Group Roles Virtual router: not physical. Active router: router that receives data sent to virtual router. Standby router: backup to active.
HSRP configuration (config)#int fa0/1 (config-if)#standby 10 ip (config-if)#standby 10 name my_test (config-if)#standby 10 priority 110
HSRP check settings show standby show standby brief
HSRP Load Balancing Can be done using different routers per vlan.
VRRP Virtual Router Redundancy Protocol. Multiple routers use a single virtual router. One router is the active, one is standby, the rest are listening. Active router is MASTER
VRRP specifics If a real ip is used that router is MASTER, if virtual ip is used then router with highest priority is MASTER. One MASTER, and one or more backup routers. Master uses vrrp messages to update status.
VRRP Load Balancing Shared between multiple virtual routers.
GLBP Gateway Load Balancing Protocol. Active/active. Multicast UDP port 3222.
GLBP load sharing Traffic from LAN is shared by multiple routers.
GLBP Multiple Virtual Routers Up to 1024 virtual routers and 4 virtual forwarders per group.
GLBP Configuration (config-if)#glbp 10 ip (config-if)#glbp name my-example (config-if)#glbp priority 110
SYSLOG debug 7, info 6, notify 5, warning 4, error 3, critical 2, alert 1, emergency 0
SYSLOG Configuration (config)#logging trap notify All results level 5 and lower will be logged.
SNMPv2 Supports plain text auth with MD5 or SHA. Can be configured for to use TCP. GET BULK
SNMPv3 Supports strong auth with MD5 or SHA with encryption DES or DES-256. Can use GET BULK and TCP.
MIB Management Information Base. A device where all the data is stored and organized.
SNMP Configuration (config)#snmp-server community backpack my_syslog_server rw
NetFlow Collects ip traffic info. Used for baselining, usage-based network billing, network design and planning, network security, and DOS/DDOS monitoring.
NetFlow stats Source/Destination ip's and ports, layer 3 protocol, TOS marking.
NetFlow Configuration (config-if)#ip flow ingress (config-if)#ip flow egress (config)#ip flow-export destination 8025 (config)#ip flow-export version 9 (config)#ip flow-export source loopback 25
Speed & Duplex Configuration (config-if)#speed 100 (config-if)#duplex full
CPE Customer Premises Equipment. Owned by the customer and owned by them.
Demarcation Point Where the ISP responsibility ends. Usually a device (modem/router/switch) owned by the ISP in the customer's media closet.
Local loop Connects the demarc to the closest switching office (central office).
Central Office Also referred to as the POP (Point Of Presence)
Toll network A trunk line inside the ISP's network, made up of switches and facilities.
Leased lines Dedicated, point-to-point. From one CPE, through the ISP's network, to another CPE on the other side.
Circuit switching Shared link with other subscribers on the node, connection must be established first. Uses dial-up modems.
Packet switching Sharing bandwidth with other subscribers to save money.
PPP Point-to-Point Protocol. Can be used between different vendors. Allows auth and multiple connections over the asynchronous and synchronous links. Async connection = 10Mbps download/5Mbps upload. Sync connection = 10Mbps/10Mbps.
MPLS MultiProtocol Label Switching. Packets imposed with a label and then forwarded based on the label alone.
ATM Asynchronous Transfer Mode. Cells 53-bytes in length.
DSL Digital Subscriber Line. Symmetrical = download/upload speeds are the same. Asymmetrical = download/upload speeds are different.
HDLC High-level Data-Link Control. Default ppp encapsulation for Cisco routers over leased lines.
LCP Link Control Protocol. Possible settings: Authentication, Compression, Error detection, Multilink, PPP callback.
PAP Password Authentication Protocol. PPP authentication method that is only done during initial link connection. Passwords sent in clear text.
CHAP Challenge Handshake Authentication Protocol. Occasional checks are performed during the connection to verify hosts.
CIR Committed Information Rate. The promised data rate that a provider sets aside for a customer on a Frame Relay network.
DLCI Data Link Connection Identifiers. Identify PVC's in Frame Relay. Inverse ARP is used to map DLCI to an ip.
LMI Local Management Interface. Keepalive messages verify connectivity.
Created by: marallander