Some notes from the Cisco CCNA Certification Study Guide

Cisco Networking

** note – this is several years old now – but much of it is still useful **

Cisco CCNA Certification Study Guide

Ctrl+Shift+6 then X – Allows you to open more than one telnet session.

Only the Hardware addresses change when packets go through routers.

Half duplex Ethernet – One station can only send or receive at any time.

Ethernet Frame – 64bytes Min 1518bytes Maximum.

ISL frames are 1522bytes long, this can be mistaken for Giants and lost. Have to use ISL NIC cards. On router interface use ‘encapsulation isl 2’ to use ISL frames on VLAN 2.

FX and SX are fibre media, 100VG-AnyLAN is twisted pair copper media.

Spanning Tree is IEEE 802.1d – created by DEC (Digital Equipment Corp).

BPDUs are Multicast frames, sent every 2 seconds. Blocked ports still receive BDPUs.

Forward delay – Time taken from listening to learning (approx 50 seconds)

Default IEEE bridge priority 32,768, used to select root bridge. If these are identical then switch with lowest MAC address is used.

ISDN Protocols – E = Telephone network standards, I = Concepts, Terminology, Q = Switching, Signalling methods.

ISDN Reference Points – R = non-ISDN device and TA, S/T = references point between NT1 and NT2, U = NT1 and ISDN network (US only)

TE1 = Device compatible with ISDN, TE2 = Device NOT compatible with ISDN, TA = Converts non ISDN signals to ISDN signals, NT1 = Converts 4 wires into 2 wire local loop, NT2 = Providers equipment (Switch, PBX)

BRI – 2 * B-channel 64kbps, 1 * D-channel 16kbps (D-channel – LAPD)

PRI (Europe, Aus) – 30 * B-channel 64kbps, 1 * D-channel 64kbps (20.48Mbps)

PRI (EUS, Japan) – 23 * B-channel 64kbps, 1 * D-channel 64kbps (1.544Mbps)

ISDN supports IP, IPX, Appletalk…

ISDN can use PPP, HDLC, LAPD, each B-channel needs a SPID

Use static routes for ISDN otherwise it will keep link open.

MAC address 48 bits (12 Hex), IPX address 80 bits.

Netware 3.11 (1983-) – ethernet_802.3/novell-ether (Cisco default on Ethernet networks), Netware 3.12 or later (1985-) – Ethernet_802.2/sap – includes LLC, Ethernet_II – arpa, Ethernet_SNAP – snap, Netware 4.11 – use sap, Netware 5 uses IP

Novell RIP – Metrics = ticks and hops (15 max), 60 sec updates (tick = 55ms / 1/18 sec)

Novell 4.11 > uses NLSP (Netware Link Service Protocol) Link State Routing

SAP – Updates 60 Secs – 4 = Netware file server, 7 = Print server, 24 = Remote bridge server

Ping Responses – U = unreachable, C = congestion, I = user interrupt,? = unknown packet type, & = lifetime exceeded

Trace Responses – N = Network unreachable, !H = Not forwarded due to ACL restriction, P = Protocol unreachable, U = Port could not be reached

Ethernet 5-4-3 rule = Between 2 nodes there can only be max 5 segments, 4 repeaters and only 3 segments must have users.

80/20 rule – 80% of traffic should be local 20% across backbone

Class 1 repeater (translational) – delay 140 secs, number you can use 1

Class 2 repeater (transparent) – delay 92 secs, number you can use 2

CSMA/CD – Used on half duplex devices

Auto-negotiate on FastEthernet checks link speed and duplex of line.

Protocol field in IP header – TCP = 6, UDP = 17, ICMP = 1, IGRP = 9

Ports – 20 FTP data, 21 FTP program, 23 – telnet, 25 – SMTP, 69 – TFTP, 53 – DNS, 80 – HTTP

Loopback address –

ACL – Standard ACL as close to destination as possible, Extended ACL as close to source as possible

IP = 1-99, Ex IP = 100-199, AppleTalk = 600-699, IPX = 800-899, Ex IPX = 900-999, IPX SAP = 1000-1099

Remember that there is an explicit ACL of ‘deny all’ if no statements match.

Multiprotocol routing supports more than one routing protocol, allows a router to deliver packets from several routed protocols.

Core Layer – High speed switching – free from filtering or anything which will slow packets etc.

Distribution Layer – Packet manipulation, address area segregation, broadcast domains, VLANs, security (ROUTERS), WAN access, queuing, firewalls, multicast domains, ACLs

Access Layer – End users, ACL/filters, remote access, shared bandwidth (SWITCHES), segmentation, DDR

HSSI – 52Mbps max

ATM cell size – 53bytes

Cisco LMI – DLCI – 16-1007, ANSI LMI – DLCI 16-992 (DLCI = 10bits)

LMI is a special DLCI = 1023

LMI Multicasting reserved for 1019-1022

LMI extensions – Virtual circuit status, multicasting, global addressing, simple flow control

LMI types Cisco (default), ansi, q933a. From IOS 11.2 LMI is auto-sensed

Class A – 1-126

Class B – 128.1-191.255

Class C 192.0.1-

Class D – (1110 highest order bits) – remaining bits for multicasting

Class E – (1111 highest order bits) – Reserved for future use

RIP 1 (Classful), single subnet, periodic updates of full routing table, max hop count 15

RIP 2 (Classless addressing), triggered updates, full routing table updates

Directed Broadcast – All host bits set to 1 received by all hosts on local broadcast domain.

Local Broadcast ( – All bits set to 1 received by all hosts on local and remote broadcast domains.

Synchronous serial links default to HDLC on Cisco routers

VIP cards – type slot/port adapter/interface (e.g e/1/0/2) (remember first interface is 0 not 1)

IGRP Metrics – Delay, Bandwidth

Default route – ip route – need to use ‘ip classless’ (Classless is enabled by default on IOS 12.x) (Only work on stub networks)

ip default-network

CDP timer default 90 secs, holdtime 240 secs

Trunked links – FastEthernet or GigabitEthernet only

Frame Tagging – ISL = Adds it’s own FCS, Cisco propriety (default), IEEE 802.1q

LAN Emulation (LANE) – Used for multiple VLANS over ATM

802.10 – FDDI Frame Tagging

Hosts can only communicate between VLANS using Layer 3 devices

VTP Modes – Server (Default for Catalyst switches) Need at least one server in a VTP domain. All changes are advertised. Client – Sends and receives updates. To make a switch a server make it a client first then promote it once it’s VTP database has received the latest revision. Transparent – Does not participate in VTP domain, but forwards VTP ads through trunked links. They keep their own database.

VTP adverts sent every 5 mins or when a change occurs, changes only kept by other switches if higher rev no than their current version.

VTP pruning – If a switch does not have any ports configured for VLAN 5 then it won’t receive updates for it. Disabled by default. Enabled across entire domain if configured. VLAN 1 is not pruning eligible.

Config Reg – 00 Rom Monitor, 01 Boot Image from ROM, 02-F NVRAM, Bit 6 set to 1 to ignore NVRAM. Register is 16 Bits.

1900 Switch Config – enable password level 1 – usermode, level 15 – enable password.

1900 switch can have up to 64 VLANS. You cannot telnet from a switch but you can telnet into it.

Administrative Distances

Routing Protocol Administrative Distance

Connected Intf 0

OSPF 110

Static route 1

RIP 120



IGRP 100

RIP – Updates 30 secs, Max Hops 15, Invalid 90 secs, Flush 240 secs, metrics hops, load balance 6 equal cost links

IGRP – Updates 90 secs, max hops 255 (default 100), invalid 3×90 secs, holddown 3×90+10 secs, flush 7×90 secs, metrics bandwidth, delay, load balance upto 6 unequal cost links.

When routers are converging no data is sent.

Frame Relay – 64 kbps – 1.544 Mbps, non-broadcast multi-access encapsulation (NBMA), dynamic bandwidth allocation, congestion control. Can use PVC and SVCs, PVC more common. Virtual circuit established before data sent. Encapsulation Cisco (Default), IETF (use when connecting non-cisco routers). Static routes are more stable than IARP.

Routers are DTE devices by default, DCE interfaces need a clock rate.

Telneting uses layers 1-4 so a good test of functionality. If you type a command the router doesn’t know or type and IP address it will try to resolve the name and telnet.

Bandwidth command sets cost for serial links. This is only used by routing protocols so they can ‘cost’ paths. Default = 1.544kbps (T1) Command is in Kbps.

Clock rate command is in bps.

HDLC – Connection-orientated, operates at the datalink layer, small overhead, no way of distinguishing network protocols. Every vendors implementation is different, NO authentication, CISCO Default over serial lines.

LAPB – Connection-orientated, datalink layer protocol, HUGE overhead, uses windowing, used instead of HDLC for error prone links.

PPP – industry standard, used when connection between different vendors devices. NCP to identify network protocol, authentication, compatible with async + sync links, operates at physical + datalink layers only. PAP – insecure authentication, CHAP auth provides initial + periodic auth. PPP compression uses stacker and predictor methods. Error detection – PPP uses quality and magic number methods. Multilink – IOS 11.1 only, spreads the load over 2 parallel circuits (bundle).

Ethernet 0 is up, line protocol is down – keepalive or framing issue, check keepalives on both sides should match, check clocking on DCE, check encapsulation on both ends.

Ethernet 0 is down, protocol is down, – carrier detect is not present, other end maybe administratively shutdown or interface or cable problem.

Ethernet 0 is administratively shutdown – the ‘no shutdown’ command has not been issued on the interface.

Show interface serial 0 – shows bandwidth, MTU, keepalives.

MTU default = 1500bytes.

Bandwidth default = 1.544Kbps (T1)

Keepalives default = 10 seconds.

Use a cross over cable to connect devices of the same type (e.g router Ethernet intf to router Ethernet intf)

Cross over cables swap pins 1 and 3 RD, and pins 2 and 6 TX

STP – 10-100Mbps – 100metres

ScTP – 10-100Mbps – 100metres

UTP – 10-100Mbps – 100metres

Coax – Coaxial – 500metres

Fiber – Single Mode upto 3000metres

Fiber – Multimode upto 2000metres

Connectionless protocols rely on application layer protocols for error handling and delivery.

EIGRP holds separate routing tables for IP,IPX,Appletalk, but only uses one protocol to distribute the updates.

CDP uses SNAP (Subnetwork Access Protocol) to enable neighbouring devices to exchange data.

IPX NLSP – link-state routing protocol intended to replace IPX RIP and SAP

NCP – Netware Core Protocol – Provides clients with access to server resources

IPX SAP – Sent every 60 seconds – includes all known services.

sap is Cisco default for Token Ring networks, SNAP is default for FDDI networks

VTP allows VLANs to be trunked over Ethernet, ATM, LANE or FDDI

Gigabit Ethernet using Multimode Fibre can run up to 260m

100BaseFX up to 400m

VLAN Management Policy Server – Must be configured with all hosts’ MAC addresses for dynamic allocation.

Standard ping – 5*100 byte ICMP echos, time out 2 seconds

DHCP uses UDP packets

Passive interface command stops interface sending routing updates, but still receives them.

2 ways to configure VLAN membership, statically or dynamically through VLAN Management Policy Server.

ISL and Trunk protocol used to configure trunking on a switch.

Pre 10.3 IOS commands Config Net – copy config from tftp to DRAM Config Mem – copy NVRAM to DRAM

IP routing table [administrative distance/composite metric]

IPX routing table [ticks/hops]