CCNA INTRO Exam Tips

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[edit section] CCNA INTRO TIPS

Here are some tips written by Cbrzana. You can discuss these tips and contribute at the forum. Contributing at the wiki is acceptable as well. These are written in "One Tip Per Day" format so you can get your daily dose. Scroll down to end of page, start reading from Day 1 and work your way up.

[edit section] INTRO TIPS

Day 34
An example of a Layer 1 connectivity issue is excessive Ethernet collisions.

Day 33
In PC to Router Connections, communicating via TCP/IP requires a crossover cable.
When using the console port, a rollover cable is required.

Day 32
In setup mode, to exit without saving changes:
exit
-or-
ctrl + c

Day 31
PPP Link Control Protocol (LCP): applies regardless of the L3 protocol

PPP Control Protocol (CP): Layer 3 specific, multiple protocols

Day 30
10-Gigabit Ethernet allows only point-to-point topology, allows only full duplex, and specifies only optical connections.

Day 29
Cable modems send/receive at different frequencies. Downstream data addressing is called Multimedia Cable Network System (MCNS), and the modulation used is QAM (64 or 256). Upstream data uses QPSK or QAM-16 modulation.

Day 28
IP Header Port Numbers
ICMP = 1
TCP = 6
UDP = 17
IPv6 = 41
GRE = 47
ICMP (IPv6) = 58
EIGRP = 88
OSPF = 89

Day 27
ISDN BRI = 2B + D
ISDN PRI = 23B + D
ISDN PRI (Non-US) = 30B + D

Day 26
ATM uses Virtual Path Identifiers/Virtuals Channel Identifiers (VPI/VCI) in the headers

Day 25
To conserve addresses, NAT also uses Port Address Translation (PAT) to disguise the port number as well.

Day 24
UDP headers consist of Destination/Source Port, Length, and Checksum. The total number of bits is 48.

TCP headers consist of Source/Destination address, SYN and ACK fields, data offset, reserved, flag, window, checksum, urgent, and options/padding fields. The total number of bytes is 20.

Day 23
Cable modems receive/send data at different frequencies.

Day 22
Use the command show ip arp to display the ARP cache.

Day 21
Fast Ethernet = 802.3u
Gigabit Ethernet (electrical) = 802.3ab
Gigabit Ethernet (optical) = 802.3z
10 Gigabit Ethernet = 802.3ae

Day 20
DCE cabling has female ends;
DTE has male

Day 19
CSMA/ Coliision Avoidance is used on wireless networks (802.11)

Day 18
To set up a HyperTerminal connection on a COM port, settings should be:
9600bps, 8 data bits, no parity, 1 stop bit, no flow control

Day 17
The default loading order for IOS is: Flash, TFTP, ROM

Day 16
ISL: Inter-switch Link, fully encapsulates with 26-byte header, 4-byte CRC trailer

802.1q: Adds 4-byte header after destination MAC address, FCS needs to be recalculated

BOTH use 12-bit VLAN ID, source/dest MAC address for switches, support separate STP instances per VLAN

Day 15
When asked to find the available number of subnets, the formula is USUALLY 2^n - 2, where n is the number of subnet bits. However, if using a classless/VLSM/RIPv2, OSPF, Integrated IS-IS, or EIGRP, the formula is just 2^n (subnet 0 and subnet 255 are not reserved).

Day 14
Cisco Discovery Protocol (CDP) learns the following of routers/switches:

1) Device Identifier (hostname)
2) Address List (Datalink and Network address)
3) Port Identifier (interface)
4) Capabilities List (router or switch?)
5) Platform (OS and Model)

Day 13
The router's configuration register is 16-bits, represented as 4 hex numbers, with the last 4 bits designated as the boot field.

0102 = ROMMON
1102 = RxBoot Mode
[2-F]102 = Full IOS

Also, 0x2142 is used to ignore the startup-config (to reset passwords).

Day 12
To enable debug (syslog) messages on a telnet connection, use the command terminal monitor.

Day 11
There are 3 different commands that will delete the startup-config:

1) erase nvram:
2) erase startup-config
3) write erase

Day 10
A crossover cable connects similar devices (switch to switch, PC to PC). The exception is switch to hub, or PC directly to router. Pin 1 connects to Pin 3, Pin 2 to Pin 6.

A rollover cable connects console to router. Pin 1 to Pin 8, Pin 2 to Pin 7, etc.

A straight-through cable connects router to PC, modem to AUX port of router. Pin 1 to Pin 1, Pin 2 to Pin 2, etc.

Day 9
Border Gateway Protocol (BGP) uses TCP and advertises routes with Autonomous System Numbers (ASN) to avoid loops.

Day 8
Frame Relay uses DLCI (Data Link Connection Identifiers) to identify virtual circuits.

Day 7
HDLC is point-to-point protocol used on leased-lines, and does not support authentication.

Day 6
Classless routing protocols advertise their subnet mask along with the subnet address; classful routing only advertises the subnet address (default subnet mask assigned).

Day 5
ATM is the data-link layer (L2) services that run over SONET, and transfer 53 byte cells (48 data, 5 header)

Day 4
To suspend a telnet connection, press ctrl+shift+6, followed by letter x.

Day 3
The maximum hop count for Routing Information Protocol (RIP) is 15 (after count reaches 16, discards packet).

Day 2
RAM contains the running-config
NVRAM contains the startup-config
ROM starts/maintains the router (bootstrap)
Flash holds the IOS

Day 1
Switch processing consists of either:
Cut-through: Transmits frame after destination known.
Fragment-free: Transmits frame after first 64 bytes
Store and Forward: Receives entire frame, and then forwards.

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