My CCNA notes (living document)

zrockstarzrockstar Member Posts: 378
I know there are are a few notes threads around here, but I wanted to make my own notes thread for me, and hopefully it will help others out too. I want this to be a living document, meaning I will update it, and would appreciate the help of the community to recommend any corrections or additions. A little about me, I just finished an academy program at my community college, and I am doing final study preparations before taking the test. I feel pretty solid with the basic concepts, so most of these notes will likely relate to ICND2 material. Thanks.

Spanning Tree Protocol (STP)
Defined by IEEE 802.1D
Purpose: Prevent switching loops in redundant path networks.

Key Terms
  • Bridge ID – Combination of the bridge priority, default is 32768 and the MAC address if the switch
  • Root – Switch with the LOWEST bridge ID
  • Bridge Protocol Data Unit – Ethernet frame that contains the BID and cost to root, used in root election, sent by all switches until converged then only by root after convergence
STP States
  • Blocking – Frames are not forwarded, but BPDUs are accepted (nondesignated ports)
  • Listening – Frames are not forwarded, MAC table is not populated, can send and receive BPDUs
  • Learning – Frames are not forwarded, but MAC table is built and populated
  • Forwarding – Frames forwarded, continues to populate MAC table
  • Disabled – cannot accept BPDU or frames (shutdown)
  • Root is chosen as the switch with the lowest BID (priority and MAC combo)
  • Root puts all connected ports in forwarding state
  • Switches in the same spanning tree will designate a root port as the lowest cost (fastest speed) to the root switch, if line speeds are equal, lowest port number becomes root port
  • Two directly connected, nonroot switches will elect designated bridge as the lower cost to root, or the lowest BID, this switch will become the designated bridge
  • The port on the designated bridge will forward, the port on the nondesignated bridge will block
Port Speeds
  • 10Mbps = 100
  • 100Mbps = 19
  • 1Gbps = 4
  • 10Gbps = 2
  • Root cost is incremented as a BPDU travels through the network on the receiving end, not sending end (leaves root as 0)
  • Hello BPDU – 2 seconds
  • Max Age – 20 seconds (time to wait after not receiving a root hello before restarting STP algorithm)
  • Forward Delay – 15 seconds (time allotted for each stage of listening and learning before proceeding to next stage, 30 seconds total)
  • Changing times will only be effective on root switch, but not recommended because of loop possibility
  • show spanning-tree (vlan) – shows Root ID, local BID, port forwarding/blocking states

Cisco Proprietary
Purpose: Brings up ports faster by bypassing the listening and learning STP states and going directly to forwarding when activated. Can only be used on ports connecting to end-user devices, not for trunk ports!

  • (config-if)# spanning-tree portfast

Rapid Spanning Tree Protocol (RSTP)
Defined by IEEE 802.1W

Key Information
  • RSTP triggers topology changes when any port other than an edge port goes into the forwarding state
  • BPDUs are sent by every switch in the RSTP tree at the same 2 second interval, if 3 consecutive BPDUs are not received, the link is considered down
Port Roles
  • Root Port – Same as STP
  • Alternate Port – Same as STP blocking port
  • Backup Port – Used with dual connections to the same physical segment
  • Edge Port – Access port, connects to an end user device, state changes do not trigger RSTP algorithm or election process, acts the same way as an STP port with Cisco Portfast enabled
  • Point-to-Point Port – Any port that connects to another switch in full duplex mode
  • Discarding – The initial RSTP state, combines STP disabled, blocking, and listening states
  • Learning – Same as STP, doesn’t process frames, but populates MAC address table
  • Forwarding – Same as STP, forwards frames, populates MAC table

Per-VLAN Spanning Tree Protocol (PVST)
Purpose: Creates a separate instance of STP for each VLAN on the network

Key Information
  • Default spanning tree mode on catalyst switches
  • Allows load balancing between VLANs
  • Sometimes referred to as PVST+

Purpose: Aggregates 2-8 switch links to load balance

Key Information
  • Can aggregate 2-8 Ethernet trunk links
  • STP considers the EtherChannel to be one link
  • Even if all but one link in the channel fails, STP algorithm will not be triggered
  • (config-int-range)# channel-group (#) mode on

Virtual Local Area Network (VLAN)
Purpose: Segments switches and breaks up broadcast domains by assigning ports to virtual LANs. Used to separate users by department, job function, etc., across one or many switches.

Key Information
  • Default VLAN on Cisco switches is VLAN 1, cannot be modified
  • Normal range range is 1-1005, 1001-1005 reserved for legacy FDDI and Token Ring support, 1006-4094 is considered extended range and is not supported by all protocols
  • Data cannot travel between VLANs without the use of a Layer 3 device
  • show vlan brief
  • show mac-address-table (vlan#)
  • vlan (#) – creates VLAN
  • name (word) – names VLAN
  • (config-if)# switchport mode (access, trunk) – changes mode for port
  • (config-if)# switchport access vlan (#) – assigns port to VLAN

ISL: Cisco proprietary, dot1q: IEEE 802.1Q
Purpose: Allows VLAN traffic over directly connected switches

Inter-Switch Link (ISL)
  • Cisco proprietary
  • Encapsulates entire frame with header and trailer
  • Does not support Native VLAN concept
  • Industry standard, not proprietary
  • Does not encapsulate frame, but adds a 4 byte header with VLAN number
  • Does not add header when forwarding Native VLAN traffic
  • show interface trunk

Switchport Modes
Purpose: Designates the role of an individual port on a switch.

  • Access – Sets the port unconditionally as an access port (for end user devices)
  • Trunk – Sets the port unconditionally as a trunk port (for connections between other switches)
  • Dynamic – Attempts to negotiate the port mode as access or trunk based off of the connection on the other end of the cable
Dynamic Modes
  • Auto – Will trunk if the other end initiates trunking, if both ends are in auto they will not trunk, if other end is in desirable or trunk, a trunk will form
  • Desirable – Attempts to trunk and will form a trunk if other end is trunk on, desirable, or auto
  • Nonegotiate – Turns off interface negotiation, goes into trunk mode but Dynamic Trunking Protocol (DTP) information is not forwarded or processed
  • (config-if)# switchport mode (access, trunk, dynamic)

VLAN Trunking Protocol (VTP)
Cisco Proprietary
Purpose: Manages and distributes VLAN information among switches in the same domain

Key Information
  • Cannot be used with non-Cisco switches
  • Domain names must match and are case sensitive
  • Passwords must match and be configured on every switch in the domain if used
  • Server – Can create, modify, or delete VLANs, originates and forwards VTP advertisements every 5 minutes or when its own VTP database has been updated, stores information in NVRAM, default mode for switches, each VTP domain must have at least one server
  • Client – Cannot create, modify, or delete VLANs, stores VLAN information in running config, accepts and processes VTP advertisements with higher revision numbers than its last VTP update
  • Transparent – Forwards advertisements but does not process them, can create, modify, and delete VLANs but changes are locally significant only, stores VLAN information in NVRAM
  • vtp mode (server, client, transparent) – changes VTP mode
  • vtp domain (word) – changes VTP domain name
  • vtp password (word) – changes password
  • vtp pruning – enables VTP pruning which prevents multicast and broadcast traffic long trunk lines that do not have ports belonging to intended VLANs
  • show vtp status – displays VTP information to include mode and revision

Inter-VLAN Routing
Purpose: Route packets between different VLANs

Key Information
  • Requires a layer 3 device, Router or multi-layer switch with an available Fast or Gigabit Ethernet port
  • Link between switch and router must be a trunk link
  • Encapsulation between switch and router must match
  • Each VLAN gets configured with a subinterface on the router end
  • Encapsulation mode must be entered on the subinterface first with the VLAN number
  • The subinterface must have a valid IP address from the same subnet as the VLAN
  • The address of the subinterface becomes the default gateway for that VLAN
  • The no shutdown command must be issued on subinterfaces' parent port on the router
Commands (on router)
  • interface fa0/0.1
  • encapsulation (dot1q/ISL) (vlan#)
  • ip address (address) (subnet mask)
  • exit
  • no shutdown


  • zrockstarzrockstar Member Posts: 378
    High Data Link Control (HLDC)
    Cisco Proprietary
    Purpose: WAN encapsulation

    Key Information
    • Default encapsulation on Cisco Routers
    • Does not support password authentication
    • Only encapsulates IP
    • (config-if)# encapsulation hdlc -- loopback tests must be ran in HDLC

    Point to Point Protocol (PPP)
    Industry Standard
    Purpose: WAN encapsulation

    Key Information
    • Supports Password Authentication Protocol (PAP), Challenge Handshake Authentication Protocol (CHAP), PPP Multilink (link aggregation), and error detection and recovery
    • Can encapsulate IPX, Appletalk, and IP
    • Supports PPP callback for dial-up links
    • (config-if)# encapsulation PPP

    PPP Authentication
    Purpose: Username and Password authentication for PPP connections

    Challenge Handshake Authentication Protocol (CHAP)
    • Uses a three-way handshake to authenticate sender and receiver
    • Doesn't send password over link, instead sends a password hash
    CHAP Commands
    • (config)# username (word) password (word) -- needs to be configured on both ends
    • (config-if)# ppp authentication chap -- needs to be configured on both ends
    Password Authentication Protocol
    • No challenge or handshake
    • Password is sent in clear text

    Frame Relay
    Purpose: WAN connection through frame relay switches

    Key Information
    • Datalink Connection Identifier (DLCI) -- Layer 2 virtual circuit addresses, locally significant only, provided by frame relay provider
    • Considered Non-Broadcast Multiaccess (does not forward broadcast or multicast traffic by default)
    • Commited Information Rate (CIR) -- Bandwidth rate of frame relay link as guaranteed by service provider, some frame relay links can use more bandwidth if available
    • Permanent Virtual Circuit (PVC) -- connection is up all the time
    • Switched Virtual Circuit (SVC) -- only up when there is data to transmit
    • Frame Relay Types -- Cisco (default, uses DLCI 1023), ANSI (non-proprietary, uses DLCI 0), Q933A -- Most equipment will negotiate Frame Relay Type dynamically
    Local Management Interface (LMI)
    • LMI messages act as frame connection keepalives between the DCE/DTE
    • Influences the PVC status as active, inactive, or deleted
    • Active -- up and running normally
    • Inactive -- errors occur on the remote end
    • Deleted -- errors occur on the local end
    DLCI Mapping
    • Static Mapping -- (config-if)# frame map ip (remote IP) (Local DLCI) broadcast -- broadcast is optional, but allows broadcast and multicast traffic across the frame relay link
    • Dynamic Mapping -- achieved through Inverse ARP, maps DLCI to IP address, can produce unreliable results, can be removed with (config-if)# no frame-relay inverse-arp
    • Point to Point Subinterface Mapping -- used with dynamic routing protocols to bypass split horizon, (config-subif)# ip address (address) (mask), frame-relay interface-dlci (dlci#)
    Congestion Control
    • Forward Explicit Congestion Notification (FECN) -- congestion notification in the direction of the destination
    • Backward Explicit Congestion Notification (BECN) -- congestion notification in the direction of the source
    • ​Discard Eligible (DE) -- frames sent over the CIR or adjusted with QoS and marked as being able to be dropped if congestion occurs
    • show frame map -- verifies encapsulation type
    • show frame pvc -- shows DE, FECN, BECN count
    • show frame lmi -- shows LMI status

  • zrockstarzrockstar Member Posts: 378
    Static Routing & General Terms

    Key Information & General Terms
    • Administrative Distance -- The trustworthiness of a route, the lower the better
    • Directly connected routes have an AD of 0, and by default are the must trustworthy routes
    • Static routes have an AD of 1 and are indicated by an "S" in the routing table
    • Default Route -- represented by, and is the interface or address for sent traffic that does not match a routing table entry
    • Floating Static Route -- a static route with an altered AD to backup a dynamic routing protocol
    • Split Horizon -- a rule stating a route cannot be advertised out the interface it was received on
    • Route Poisoning -- a route advertised with an unreachable metric
    • Convergence -- all routers share the same, current routing table and are just processing updates
    • (config)# ip route (ip address) (subnet mask) (nexthop)
    • (config)# default -- ip route (nexthop add or exit int)
    • show ip route -- shows routing table

    Routing Information Protocol (RIP)

    Version 1 Key Information
    • Distance Vector Routing Protocol -- uses hop count as a metric
    • Administrative Distance -- 120
    • Update Timer -- broadcasts entire routing table throughout the network every 30 seconds
    • Invalid -- 3 times the update value, marked as unreachable with a metric of 16, default 180 seconds
    • Hold Down Timer -- How long the route is marked unreachable , default 180 seconds
    • Flush -- Total time passed until the route is removed from the table, default 240 seconds
    • Sends Version 1 updates, receives Version 1 and 2
    • Load balances over a maximum of 4 equal cost routes
    • Supports classful routing only, does not send subnet mask
    Version 2 Key Information
    • Supports classless networks, sends subnet mask with routing table
    • Multicasts routing tables to
    • (config)# router rip -- starts RIP process
    • (config-router)# version 2 -- turns on version 2 updates and VLSM support
    • (config-router)# network (ip address) (subnet mask if v2)
    • debug ip rip
    • clear ip route * -- clears routing table, can force a RIP update

    Open Shortest Path First (OSPF)

    Key Information
    • Link State Protocol -- sends updates only when topology changes, uses "hello" packets as keepalive
    • Administrative Distance -- 110
    • Routes show as "O" in routing table
    • Metric -- cost (bandwidth), calculation is 100,000,000/bps -- 1785 for 56K, 64 for T1, 10 for Ethernet, 1 for Fast Ethernet
    • Hello Packet -- allows neighboring devices to dynamically discover each other and serves as a keepalive once neighbor relationships have been established, sent every 10 seconds on broadcast networks, 30 seconds on NBMA networks, this discovery is called an adjacency
    • Adjacency Requirements -- subnet number and mask must match, hello and dead timers must match, area must match
    • Hello Timer -- how often hello packets are sent to
    • Dead Timer -- how long a router will wait to hear a hello from an adjacent router before removing the adjacency (40 seconds for broadcast networks, 120 for NBMA)
    Router Roles & Election
    • OSPF uses a designated router and backup designated routers as chosen through an OSPF election
    • OSPF election results are based off interface priority of 0-255, 0 means the router will never become the designated router, 255 means it will always become the designated router
    • If a tie occurs during election, the tie is broken by the router with the highest loopback IP address configured, or the highest interface address if loopbacks are not present
    • Designated Router (DR) -- router that collects Link State Advertisements area routers and multicasts them through the OSPF area
    • Backup Designated Router (BDR) -- will become the DR if the DR goes down
    • DROTHERS -- routers not assigned as DR/BDR
    Adjacency States
    • Down -- no hellos received but can still be sent
    • Attempt -- unicast hello packets sent to neighbor (used on NBMA networks)
    • Init -- First hello packet received, but router ID not included
    • 2-WAY -- each router has received a hello packet containing its own router ID
    • ExStart -- exchange of data can begin between DROTHERS and their DR/BDR
    • Exchange -- contain link state databases
    • Loading -- sending link state requests
    • Full -- routers have full adjacency with neighbors
    Router Types
    • Internal Router -- all interfaces are in the same OSPF area
    • Area Border Router -- at least one interface is in area 0 and connects other areas to area 0
    • Backbone Router -- connects to area 0
    OSPF Authentication Commands
    • ip ospf authentication-key (password) -- sets password, max 8 digits
    • ip ospf authentication -- enables authentication
    • ip ospf authentication message-digest -- enables MD hasing
    • ip ospf message-digest-key (#) md5 (password)
    • (config)# router ospf (process id 1-65,535 -- does NOT have to match other routers!)
    • (config-router)# network (ip address) (wildcard) area (#)
    • (config-router)# router-id (ip address) -- configures router ID for OSPF election
    • (config-if)# ip ospf network non-broadcast -- configured on serial line to use on NBMA networks since OSPF does not use split horizon
    • (config-router)# default information-originate -- propagates the default static route through the dynamic network
    • (config-if)# ip ospf priority (0-255) -- sets election priority
    • show ip ospf neighbors
    • show ip ospf interface

    Enhanced Interior Gateway Routing Protocol (EIGRP)

    Key Information
    • Cisco Proprietary
    • Administrative Distance -- 90
    • Metric -- default is a calculation of bandwidth and delay, but load and reliability can also be used
    • Uses Diffusing Update Algorithm (DUAL) to calculate metric, routes show as "D" in routing table
    • Is a distance vector routing protocol but is often referred to as a hybrid
    • Supports multi-protocol operation, VLSM/CIDR, and rapid convergance
    • Multicasts hello packets to to establish, maintain, and keepalive neighbor relationships
    • Can load balance across up to 16 unequal cost routes (default 4 when active)
    • Only send updates when topology changes
    Neighbor Relationships
    • To form an EIGRP relationship the following must match: autonomous system (AS) number and metric weights
    • DUAL query is sent to neighbors to find routes
    EIGRP Tables
    • Route Table -- contains the best routes (lowest metric) in the network
    • Topology Table -- contains all feasible routes in the network
    • Neighbor Table -- contains no routes, but EIGRP neighbors
    EIGRP Routes
    • Successor -- best route to network
    • Feasible Successor -- alternate, loop-free routes to network, the feasible successor with the lowest metric will become the successor if the successor goes down
    Topology Codes
    • P -- passive, the route is functional, this is the ideal state
    • A -- active, route is currently being calculated by DUAL
    • router eigrp (AS number -- unlike OSPF, this must match!)
    • no auto-summary -- disables network address summary on classful boundaries, highly recommended for EIGRP
    • network (IP address) (wildcard mask -- optional but recommended)
    • variance (multiple) -- enables EIGRP unequal cost load balancing
    • show ip protocol
    • show ip eigrp topology
    • show ip eigrp neighbors
    • show ip eigrp interface

  • zrockstarzrockstar Member Posts: 378
    Ipv6, nat, vpn, ipsec
  • zrockstarzrockstar Member Posts: 378
    Reserved for ACL
  • zrockstarzrockstar Member Posts: 378
    reserved for other
  • oli356oli356 Member Posts: 364
    Great post so far! I'm sure it will help others out, including myself :)
    Combination of GNS3 and Cisco equipment if required.
  • zrockstarzrockstar Member Posts: 378
    Glad to help Oli. If you notice anything that needs to be fixed, let me know. This has been helping me out a lot too. I have been scoring high in these areas on my practice test after starting this, so I think they are pretty good notes.
  • jdgstatjdgstat Registered Users Posts: 1 ■□□□□□□□□□
    Very nice zrockstar. I agree with Oli356. It'll be extremely helpful to others that are studying, including myself and 2 others here at work. I've taken CCNA classes through the a local tech school around (using the Cisco learning website), so this will be very helpful to make sure I have all areas covered. Thanks!
  • zrockstarzrockstar Member Posts: 378
    You're welcome JDG, and welcome to Tech Exams! This site has so much good info and many helpful people. Don't be afraid to ask anything while studying, everyone here will help.
  • ArystaArysta Member Posts: 58 ■■□□□□□□□□
    Thanks for this! I just started studying for the CCNA this week, so it's great timing. It's a good checklist to compare against to make sure I'm covering everything.
  • zrockstarzrockstar Member Posts: 378
    Updated with routing notes. I would appreciate it if some pros would put some eyes on this and recommend any changes/additions. Thanks.
  • nitrorednitrored Registered Users Posts: 1 ■□□□□□□□□□
    Thanks , that is really going to help me !!icon_cheers.gif
  • X10MMXX10MMX Member Posts: 81 ■■□□□□□□□□
    This is awesome.. I am currently studying for my CCNA! Thanks zrockstar
  • onesaintonesaint Member Posts: 801
    This is great. Thanks for posting it.
    Work in progress: picking up Postgres, elastisearch, redis, Cloudera, & AWS.
    Next up: eventually the RHCE and to start blogging again.

    Control Protocol; my blog of exam notes and IT randomness
  • LinuxRacrLinuxRacr Member Posts: 652 ■■■■□□□□□□
    I'm digging these notes! Thanks for posting.
    My WGU B.S. IT - Security Progress : Transferred In|Remaining|In Progress|Completed
    AGC1, CLC1, GAC1, INC1, CTV1, INT1, BVC1, TBP1, TCP1, QLT1, HHT1, QBT1, BBC1 (39 CUs), (0 CUs) (0 CUs)
    WFV1, BNC1, EAV1, EBV1, COV1 | MGC1, IWC1 | CQV1, CNV1, IWT1, RIT1 | DRV1, DSV1, TPV1, CVV1 | EUP1, EUC1, DHV1| CUV1, C173 | BOV1, CJV1, TXP1, TXC1 | TYP1, TYC1, SBT1, RGT1 (84 CUs) DONE!
  • bcall64bcall64 Member Posts: 156
    Thanks so much for posting these notes! It's a quick reference when I'm not sure about something.
  • DaniactualDaniactual Member Posts: 5 ■□□□□□□□□□
    Great post! Thanks a lot for sharing your notes...
  • synseqsynseq Member Posts: 123
    Cool. Thanks for the notes. I don't like relying on any one book or source when studying for a certification. I like to study a variety of sources because some may have better methods for studying and learning than others.
    Life is not a gift for man, man is himself life, his wants and needs serve the singular purpose of existence, any man who loses sight of this and does not cherish life itself is in the hardest of ways.
  • sthompson86sthompson86 Member Posts: 370
    I have passed my CCNA, but wow awesome notes.
    Currently Reading: Again to Carthage - CCNA/Security
  • jude56gjude56g Senior Member Member Posts: 107 ■■■□□□□□□□
  • MWJNMWJN Member Posts: 8 ■□□□□□□□□□
    Hi zrockstar congratulations on passing
    Looking to take ICND2 exam in early September
    Wonderd will you be adding notes for IPV6, NAT, VPN, IPSEC & ACL?
    Notes are really good for the ICND2 exam review & I am sure that others are finding them very useful aswell
  • dcren21dcren21 Member Posts: 71 ■■□□□□□□□□
    Thanks for posting these notes. They are helpful.
    WGU B.S. IT - Security (Start Date 8/1/12) : Transferred | Required | In Progress | Completed
  • j.petrovj.petrov Member Posts: 282
    Awesome Notes! thanks a ton!
  • MWJNMWJN Member Posts: 8 ■□□□□□□□□□
    Hi ZRockstar
    Did you write up any additional notes for the IPV6, NAT, VPN, IPSEC & ACL objectives?
    Will you be posting them now that you have passed the CCNA, Congratulations
    Will be taking the exam soon in September and was impressed by how easy and simple you had made the topics for exam review
    Many thanks
  • zrockstarzrockstar Member Posts: 378
    MWJN wrote: »
    Hi ZRockstar
    Did you write up any additional notes for the IPV6, NAT, VPN, IPSEC & ACL objectives?
    Will you be posting them now that you have passed the CCNA, Congratulations
    Will be taking the exam soon in September and was impressed by how easy and simple you had made the topics for exam review
    Many thanks

    Thanks MW I have them written by hand, I will review them to see if I can easily transcribe them into the same format.
  • MWJNMWJN Member Posts: 8 ■□□□□□□□□□
    Hi ZRockstar
    Many thanks
    Look forward to seeing them for reviewing and others will agree
    Thanks again
  • NetworkVeteranNetworkVeteran Member Posts: 2,338 ■■■■■■■■□□
    High Data Link Control (HLDC)
    It's HDLC not HLDC and that stands for High-Level Data Link Control.

    Cisco Proprietary
    HDLC is not Cisco-proprietary. cHDLC (Cisco HDLC) is!
    Only encapsulates IP
    This is certainly not true. I just checked one of my cHDLC links and a 30-section capture caught CLNP, IS-IS, CDP, SLARP, and ES-IS. CLNP is a network-layer alternative to IP.
  • NetworkVeteranNetworkVeteran Member Posts: 2,338 ■■■■■■■■□□
    1001-1005 reserved for legacy FDDI and Token Ring support
    That should be 1002-1005.
  • NetworkVeteranNetworkVeteran Member Posts: 2,338 ■■■■■■■■□□
    (config-router)# network (ip address) (subnet mask if v2)
    Unfortunately, no. You cannot provide a subnet mask in your RIPv2 network commands.
  • zrockstarzrockstar Member Posts: 378
    Thanks NV, it's not letting me edit my previous posts. I'll try to figure it out tomorrow and make the changes.
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