Category Archives: CCDA

CCDA Notes – WAN

Additions/subtractions needed? Let me know.

WAN Categories

  1. Circuit Switched – created only when needed. i.e. ISDN and dial-up.
  2. Leased Lines – dedicated connection. TDM based.
  3. Packet switched – shared bandwidth using virtual circuits. i.e. Frame Relay.
  4. Cell Switched – ATM
  5. Broadband – xDSL, Cable, Wireless

Time Division Multiplexing (TDM)

  1.  Multiple channels such as voice, video, and data can be combined
  2. DS1 or T1 provides 24 time slots of 64kbps each and one 8 kbps control time slot

Frame Relay

  1. NBMA
  2. DLCI = L2 addressing
  3. LMI reports VC status.
  4. LMI has 3 types. Cisco, ANSI, Q.933A. Auto tries all three.
  5. Multipoint interfaces require L2-to-L3 address resolution. Done via inverse-ARP or static “frame-relay map”.
  6. Physical interface is multipoint by default. i.e Serial0/1
  7. Static L2-to-L3 mappings override dynamic mappings.
  8. “frame-relay interface-dlci <dlci #>” on point-to-point subifs. LMI does not communicate DLCI number on subifs.


  1.  Enabled automatically when a supported protocol is cfgd. i.e. “ip address”
  2. Requests are sent out all circuits assigned to the interface for all supported protocols.
  3. Requests can be disabled via “no frame-relay inverse-arp”. Replies can not be disabled.
  4. Automatically supports multicast/broadcast via a replicated unicast.


  1. Circuit-based ring topology.
  2. Optical
  3. ATM or Packet Over SONET(POS)
  4. Optical carrier rates. i.e. OC-1 =51.85 Mbps  OC-255=13.21 Gbps

CCDA – Enterprise Composite Model

More notes.

Enterprise Composite Model
1) Still leverages the hierarchical model.
2) Modular:
    a) Enterprise Campus
    b) Enterprise Edge
    c) Enterprise WAN
    d) Enterprise Data Center
    e) Enterprise Branch
    f) Enterprise Teleworker
3) Enterprise Campus consists of:
    a) Campus Core
    b) Building Distribution
    c) Building Access
    d) Edge Distribution
    e) Server Farm / Data Center
4) Enterprise Edge consists of:
    a) E-Commerce
    b) Internet / DMZ
    c) VPN / Remote Access
    d) Enterprise WAN
5) Service Prodvider Edge consists of:
    a) Internet
    b) PSTN
    c) WAN Services
6) Remote modules:
    a) Enterprise Branch – site-to-site VPNs
    b) Enterprise Data Center – high speed LAN
    c) Enterprise Teleworker – remote access VPNs

CCDA Notes – Hierarchical Model

Missing anything? Let me know and I’ll update/correct.

Hierarchical Model
1) Easy to understand
2) Cost savings
3) Modular
4) Easily modified
5) Facilitates summarization
6) Fault isolation

Core Layer
1) Move data as quickly as possible
2) Reliability
3) Redundancy
4) Fault tolerance
5) No filters or other overhead
6) Limited, consistent diameter

Distribution Layer
1) Implement policies
2) Security
3) QoS
4) Redundancy and load balancing
5) Summarization
6) Policy routing
7) Routing between VLANs
8) Redistribution
9) Media translations
10) Define multicast and broadcast domains

Access Layer
1) High availability
2) Port security, ARP inspection, VACLs
3) Broadcast control
4) QoS and trust boundary definition
5) PoE
6) STP

CCDA Notes – Best Practices

Do you agree with the checklist and best practices mentioned below? Do you know any that should be added to these lists. Let me know and I’ll get them added if they are pertinent.

Network Health Checklist
1) Ethernet segments should not have a sustained utilization of 40% or higher.
2) All Ethernet segments should be switched. No shared segments(hub-based).
3) No WAN links should feature a sustained utilization of 70% or higher.
4) WAN response times should be generally less than 100ms.
5) LAN response times should be around 2ms.
6) No segments have more than one CRC error per MB of data.
7) Segments should be no more than 20% multicast/broadcast traffic.
8) Device CPU utilization should not exceed 75% over 5 minute intervals.
9) Output queue drops should not exceed 100 in an hour.
10) Input queue drops should not exceed 50 in an hour.
11) Buffer misses should not exceed 25 in an hour.
12) Ignored packets should not exceed 10 in an hour.

Access Layer Best Practices
1) QoS for performance.
2) Redundancy for availability.
3) Limit VLANs to a single closet.
4) RPVST+ instead of STP or PVST+.
5) DTP set to desirable/desirable. ** I do not agree with this one **
6) VTP transparent mode.
7) Disable trunk mode on access ports.
8) Routing in the access layer.
9) Portfast on edge ports.

Distribution Layer Best Practices
1) Aggregate bandwidth together into EtherChannels.
2) QoS.
3) Security mechanisms.
4) FHRP protocols.
5) Routing.
6) Address summarization.
7) Triangles and not squares for redundancy in and between layers.

Core Layer Best Practices
1) Redundant triangle designs between switches.
2) Fast switching at Layer 2. No routing if possible.
3) Multilayer switches.


This starts my foray into the CCDA. I will try to keep the CCDA notes blog posts to a specific topic per post. If you see any mistakes, missed subject matter, or just wish to berate my note taking skills then feel free to leave a comment.


1) Business objectives. Identify technologies and develop a strategy.
2) Identify customer requirements.
    a) Speak with all managers.
    b) Follow these steps:
     Step 1. Identify network applications and services.
     Step 2. Define organizational goals.
     Step 3. Define organizational constraints.
     Step 4. Define technical goals.
     Step 5. Define technical constraints.

1) Characterize and asses the network to develop a project plan.
2) Information gathering.
    Step 1. Identify and gather all existing documentation.
    Step 2. Audit the network.
    Step 3. Perform traffic analysis.
3) Information to gather:
    a) Device list
    b) Hardware models
    c) Software versions
    d) Configs
    e) Auditing tools output
    f) Interface speeds
    g) Link, cpu, and memory utilization
    h) WAN technologies

1) Top Down Approach
    a) Start with apps and work your way down to the network infrastructure.
    b) Accurately incorporates the business drivers.
    c) Disadvantage is that it is time-consuming.
2) Bottom Up Approach
    a) Based on previous experience.
    b) Allows for quick solutions.
    c) Might make for inappropriate solutions.
    d) Often misses the organizational goals.
3) Pilots and prototypes
    a) Prototype – A subset of a full network. These networks are generally isolated from production network.
    b) Pilot – A live location for testing on the actual network. Allows the discovery of any real issues.
4) A design document generally includes:
    a) Introduction
    b) Design requirements
    c) Existing network infrastructure
    d) Design
    e) PoC
    f) Implementation plan
    g) Appendices

1) Follow the project plan and design document.
2) Each step should include:
    a) Description
    b) Implementation guidelines
    c) Estimated time to complete
    d) Rollback steps
    e) Reference information

1) Network management
2) Network monitoring
3) Routine maintenance
4) Upgrades
5) Performance management
6) Network fault detection and correction

1) Be proactive instead of reactive
2) This may lead back to the Prepare phase and start the process all over.