The two most significant things to study on the test are the
OSI model and TCP/IP addressing and subnetting.
If you know both of those very, very well, then you are guaranteed about
50% on the exam. The rest comes from
this sheet.
The last bit of advice is that you didn’t believe me on the
importance of knowing the OSI model, learn it backwards, forwards, sideways,
and be prepared to answer really nit-picky questions about it.
OSI Model
Application
File,
print, message, database, and applications
Determines
availability of the target host.
www,
email, ftp, telnet, edi, quake
Presentation
Determines
the syntax of the data transfer.
Pict,
tiff, jpet, midi, mpeg, quicktime, etc
Session
Dialog
control, coordinates the comunications
Nfs,
sql, rpc, x windows, asp (appletalk session protocol), DNA SCP (digital
whatzit)
Transport
End-to-end
communication
Responsible
for hiding the communications from the higher layers.
TCP
/ UDP
Network
Routing
IP /
ICMP, BootP, ARP, RARP
Routers
Data Link
Framing
Ethernet II, 802.5 (token ring),
802.3, 802.2 (802.3 with dsap and ssap logical link control fields)
Media access control: MAC: 48
bits, 3 bytes vendor + 3 bytes serial number
WAN:
High-level datalink control HDLC
(cisco default for serial links)
Synchronous Data Link Control SDLC
(uses polling)
Link Access Procedure, Balanced
LAPB
x.25, slip, ppp, isdn, Frame Relay
Bridges / Switches
Physical
Wire…
v.24,
v.35, x.21, g.703, hssi, etc
Repeaters
/ Hubs
DOD Model
Process/application
à application,
presentation, session
Host-to-host à transport
Internet à network
Network
access à Datalink
/ physical
LAN
Ethernet
802.3
CSMA/CD | Ethernet_II
| 802.2
10base2/thinnet:
185 meters
10base5/thicknet:
500 meters
10baseT:
can run above 10Mbps 200ish meters
5-4-3
rule: 5 segments, 4 repeaters, 3 segments populated
100BaseTX: 100 meters, up to 2 repeaters. Packets between 512 and 1518.
FDDI
100
Mbps
token
passing with dual counter-rotating rings
Token-ring
802.5
4
/ 16 Mbps
ATM
53-byte
cells
Flow
Control
Contention:
CSMA/CD : Carrier Sense Multiple Access, Collision Detect
Token
Passing: Token Ring, Fiddi
Polling:
SDLC, some HDLC, some HP ethernet stuff
SWITCHING
Store –
and – forward
Buffers
whole frame before forwarding
Cut-Through
Forward
frame as soon as destination address is available
Fragment
Free
Does Cut-Through after 64 bytes
are received to stop collision packets from being forwarded.
802.1d
Spanning-Tree Protocol STP
detect
and eliminates loops in routed network
STA:
Spanning Tree Algorithm
Sends
out BPDUs: Bridge protocol data units
VLAN:
Virtual Lans
Create
‘logical’ networks by location, function or department.. or protocol, or
whatever.
Done with a switch using
Frame-Tagging (can be used between switches if you have ISL inter-switch
link) Frame-Tagging uses unique
user-defined identifiers while within the switch fabric, and is very scalable.
TCP/IP
Port
numbers:
TCP:
protocol number 6
ftp:
21
telnet:
23
smtp:
25
UDP:
protocol number 17
Dns:
53
Tftp:
69
Snmp:
161
0-255:
public assigned
256
– 1023: assigned to companies
1023+
user defined / source addresses
IP Addressing:
Class leading bits decimal range of first byte
A 0 1-127
B 10 128-191
C 100 192-223
Learn
the rest of the stuff…. Way out of scope of this.
NOTE:
Cisco considers the mask to be the
bits beyond what is ‘normal’ for that class address, not the entire number of
bits in the subnet mask, sometimes….
IPX
Protocl
Stack:
Application,
presentation, session à RIP,
SAP, NCP, NLSP, etc…
Transport à IPX,
SPX
Network à IPX
Data
link à ODL
Open Data Link
Physical à whatever
IPX
Connectionless,
and communicates via sockets
Each
host runs its own internal ipx network in addition to any lan network
Addressing:
10
byte address
first
4 bytes are network – need to be unique, otherwise whatever..
last
6 bytes are node - usually just use the
MAC address
SPX
Sequence
Packet eXchange
Connection
oriented protocol
Creates
virtual circuits, with specific connection IDs
RIP
Routing
information protocol
Distance
vector protocol that establishes routes between ipx networks
Judges
based on ticks (1/18 second units) and hops
Broadcast
every 60 seconds
Used
to provide each server with a complete network map
SAP
Service
advertising protocol
Servers
use it to advertise, clients use it to locate services
Broadcast
every 60 seconds
NLSP
NetWare
Link Services Protocol
Link-state
protcol to replace RIP and SAP someday…
NCP
NetWare
Core Protocol
Provides
access to server resources
Netware
in a nutshell
-Strict
client-server model (nobody is both)
-Servers
provide files, printing, messaing, applications, and databases
-Every netware server (or cisco
router) creates a SAP table of all services offered by all servers
-A client issues a GNS
(GetNearestServer request) broadcast to find out what is on the local SAP
Netware
frame types Features
802.3
default on NetWare <=3.11
802.2
default on NetWare 3.12+
ethernet_ii supports
tcp/ip and ipx
ethernet_SNAP appletalk,
tcp/ip, and ipx
--- all of these are incompatible…
god love’m
Routing Protocols
RIP:
Routing Information Protocol
Distance
– vector routing protocol
Updates
every 30 seconds
Route
invalid timer 90 seconds: time before route considered invalid.
Route
flush timer: 240 seconds: route removed from table
Can
use metrics (1-15) to weight against some interfaces
15
hop limit
OSPF: Open Shortest Path First
Link-state
routing
Very
infrequent broadcast updates
Extremely
granular metrics
NLSP: Novell’s Link State Protocol
Link-state
IGRP: Interior Gateway Routing
Protocol (cisco proprietary)
Distance-vector
Metrics
and hop count from 1-255
Measures
delay in units of 10 milliseconds
Measures
bandwidth – on serial connection this needs to be set, default is T1
Measures
reliability as 1-255 (255 optimal):
Measures
load: 0-255 (0 = no-load)
Allows
multi-path routing (dual links of equal bandwidth to 1 location)
Implements
hold-downs, split horizons, and poision reverse updates
Update
timer is 90 seconds, invalid timer is 270 seconds (3 times update)
Hold
down timer is 280 (3 times update +10 seconds)
flush timer is 630
seconds (7 times update)
administrative
distances: (reliability of information)
0 = direct
connection, 1 = static, 100 = igrp, 110 =ospf, 120 = rip, 255 = unknown
EIGRP: Enhanced IGRP
Hybrid
routing protocol
Uses
distance vectors, however they are triggered by changes, not timers.
Faster
convergence, multiprotocol support
Distance-
vector:
Uses
second-hand info
Problems
detecting /closing routing loops (counting to infinity)
Judges
‘best’ based on hop counts
Convergence
can get pretty lengthy
Split
horizion: enforces that inforation is
not sent back in direction it came from
Route
poisoning: Helps prevent incorrect updates by setting route down explicitly
Hold-downs:
prevents routes from changing too quickly, to allow time for stabilization
Link-state
No-second
hand info, and understands entire network
Uses
LSP packets to build ‘personal’ copy of entire network structure to route from
LSP:
link-state packets or “hello packets”
Chooses
‘best’ path based on: bandwidth, congestion, metrics, etc.
Update
times can be set very lengthy as changes cause triggered udpates.
EXTERIOR routing protocols
EGP:
Exterior Gateway Protocol
Polls
neighbors
exchanges info
about AS with neighbors
distance vector
very simple
BGP:
Border Gateway Protocol
Can
detect routing loops
Can
work between AS
Other Random Cisco protocols
CDP:
Cisco Discovery Protocol
Runs
SNAP: SubNetwork Access Protocol at the datalink layer.
-
this allows routers running different protocols to
still communicate
-
60 second updates, 180 second hold time
#show cdp interface
interface
information, encapsulation info, and timing information
#show cdp entry <name or * for
all>
shows
detailed information about other routers on network
#show cdp neighbors
shows
summary information that is being exchanged
#show cdp neighbor detail
extended
listing of info for all routers
#show cdp traffic
shows
packets sent / received amount neighbors
WAN:
POTS
Plain
Old Telephone Service. (politely is:
pstn: public switched telephone network)
Demarc:
end of responsbility for provider, start for customer
CPE:
customer premise equipment
Local
loop: wire from CO to demarc
CO:
Central Office: provider POP : point of presence
SDLC
Synchronous
Data-Link Control
Used
originally for SNA
Point
–to-point or multipoint
Bounded
or unbounded media, half or full duplex
Circuit
or packet-switched networks
2
node types. Primay or Secondary
(controlled by primary)
HDLC
High-Level
Data-Link Control protocol
This is the default communication
method for cisco routers of sync links, and is proprietary
This came after SDLC, and was
modified into LAP and LAPB.
HDLC transfer modes:
NRM:
Normal Response Mode: secondaries only speak when spoken to by pri
ARM:
Async Response Mode: sec. can speak on own
ABM:
Async Balanced Mode: nodes can be both pri and sec
LAPB:Link
Access Procedure Balanced: built into x.25
DDR
Dial
on demand Routing
·
be sure and setup route as static, and with specified
distance over 200 to make sure it is ‘last resort’
X.25
Point-to-point
communication between DTE and DCE
DTE:
Data Terminal Equipment (router or terminal, or whatever)
DCE:
Data Circuit-Terminating Equipment (csu/dsi or modem)
PSE:
Packet Switching Exchange: switches inside carriers network
Addresses
defined by x.121 as a 14 digit number
DNIC:Data
Network Identified Code is first 4 bits of address
Rest
of address is assigned by the administrator
Full-duplex
protocol
‘overbuilt’
with lots of error checking
Created
SVC or PVC connections (switched or Permanent virtual circuits)
PLP
Packet
layer protocol
x.25’s
network layer protocol
modes:
call setup, data transfer, idle, call clearing, restarting
LAPB
Link
Access Procedure Balanced
Makes
sure frames are error free and sequenced
Types
of frames:
I information sequencing, flow control, error detect, recovery
S supervisory handles requests for, and suspension of transmittion
U unnumbered link setup and disconnections and error reporting
Setting
up X.25 on Cisco
#interface
<interface>
#encap
x25
#x25
address <14 digit number>
to
set the address
#x25
ips <bytes>
to
configure Input Packet Size
#x25
ops <bytes>
to
configure Output Packet Size
#x25
win <integer>
to
configure Window Input Size
#x25
wout <integer>
to
configure Window Output Size
Frame
Relay
Shared
Bandwidth
Can
setup a CIR (Committed Information Rate)
Assumed
error-checking is handled at another, higher, layer
PVCs
are created at layer 2.
DLCIs:
Data-link connection Identifiers : are used to identify virtual circuit
connections.
DLCI
address are assigned by the provider and then mapped to IP addresses by the
router
LMI:
Local management Interface
These
are autodetected in current IOS versions….. however:
Keyword Meaning
Cisco: defined by industry group, and default
ANSI: Annex D defined by T1.617
Q933a: Defined by ITU-T Annex A Q.933A
LMI
can be used to determine the global significance of the DLCI numbers.
Setup
of Frame Relay on Cisco
#interface
<interface>
#encapsulation
frame-relay [ietf, or default is cisco]
use default to talk to other cisco
routers, use ietf encapsulation to talk to non-cisco.
#frame-relay
interface-dlci <dlci number>
to
map dlci number to current interface, or subinterface
Then
specify an IP address for that subinterface
Optionally
you can hard-code the address on the other end.
#encap
frame-relay [ietf]
#no
inverse-arp
turns
off auto addressing features
#ip
address <ip address> <subnet mask>
#frame-relay
map ip <address> <metric ? > [cisco] [broadcast]
this
lets you mix encap types, and allow broadcast over interface
Monitoring
Frame Relay
#show
frame ?
ip
ip statistics
lmi lmi stats
map map table
pvc pvc stats – this one displays the DLCI
#
route route info
traffic protocol stats
PPP
Point
to Point Protocol
Userfull
for dial-up or sync links (ISDN)
Authenticate
using PAP: password authentication protocol or
CHAP:
Challenge Handshake Authentication Protocol
ISDN
Integrated
Services Digital Network
Terminal
equipment types:
TE1:
understands ISDN
TE2:
predates ISDN and needs a TA (terminal adapter) to work
ISDN
reference points:
R:
between non-isdn device and TA
S:
between terminal and NT2 device
T:
point between NT1 and NT2
U:
point between NT1 and carrier line
termination device
ISDN
protocol codes:
E:
existing telephone network
I:
concepts, terms, and services
Q:
switching and signaling
ISDN
service levels:
Connect
to lines with SPIDs (service Profile Identfiers) (phone numbers..)
BRI:
Basic Rate Interface: 2B + 1D
B
= 64kbs, D=16Kbps = 128kbs plus control
PRI:
Primary Rate Interface: 23B + 1D
Total
of 1.544Mbps
Configuring
ISDN BRI
#isdn
switch-type ?
tons
of proprietary switch types
#interface
<interface>
typicaly
bri0, or something like that.
#encap
ppp
ppp
is method used to setup isdn phone calls
#isdn
spid1 <spid1>
#isdn
spid2 <spid2>
Configuring
ISDN PRI
#controller
<interface> <location>
typicaly
something like #controller T1 1/0
#framing
efs
sets
Extended Super Framing, this is normal for T1/ PRI line
#linecode
b8zs
line-conding mechanism to assist
with timing by preventing strings of zeros
#pri-group
timeslots <value from 1-24>
sets
number of timeslots
Access lists:
Basics:
Access
lists must be created, then applied to an interface
Access
lists can filter incoming or outgoing from an interface
Packets
are compared only until a match is made
Packets
that do not meet any criteria on the list are discarded
Wildcard
masking:
Nifty,
acts like a reverse subnet mask:
Example:
0.0.0.255 would wildcard all hosts on class C network
0.0.0.0 would
indicate no wildcarding
keywords:
host:
0.0.0.0 : just specified host
any:
255.255.255.255: absolutely anything
*
when using keyword it comes before IP address, when using mask it comes
after!!!!
List
number scheme
List
number range meaning
1-99
ip standard list
100-199
ip extended access list
800-899
ipx standard
900-999
ipx extended access list
1000-1099 IPX
SAP access list
IP
access list creation
#access-list
<number of list> <permit | deny> <source address>
[<mask>]
IP
extended access list
#access-list
<number> <permit |deny> <protocol> <source>
<destination> <port>
source
and destination can be masked
port can
be ‘eq’ for equal, ‘neq’ not equal, ‘log’ logged, or assorted other things
port can
also be keyworeded: www, smtp, finger, ftp, telnet, etc…..
ipx
access list
#access-list
<number> <permit|deny> <source network number>
<destination network number>
no wildcarding needed with ipx
-1 is used to indicate ‘any network
address’
extended ipx access lists
#access-list <number>
<permit|deny> <protocol> <source> <socket>
<destination> <socket>
-1 still indicates ‘any’ for socket
or source address
IPX SAP access lists
#Access-list <number>
<permit|deny> <source> <service type>
service type is numeric value
Applying
Access list to Interface
#interface
<interface>
#ip
access-group <number of list> <in | out>
Monitoring:
#show
access-list
shows the lists and how many
matches for each line
#clear
access-list counters <access list number>
clears
statistics
Logging:
Keyword log can be placed at the
end of extended access lists, and info will be logged to console by default, or
could be re-directed to a error-log server
Logs include: access list number,
source and destination port/address and number of packets.
Displaying
access list info
#Show ip
interface <interface>
displays
which list is enabled for the interface, both incoming and outgoing
#show
running-config
shows
just about everything….including details of what makes up each access-list
CISCO Things:
Startup sequence
Bootstrap
from
Rom
Cisco
IOS from
Flash
From
tftp
From
Rom
Configuration
File from NVRAM
From
tftp server
From
console
Editing commands
Toggle
on/off: Terminal
editing / terminal no editing
Control
+
A move to beginning of line
E end
F forward
B back
P previous
N most recent
Show
history
Terminal
history size set buffer size
Arrow
keys also work to edit and scroll through buffer
Passwords
Enable
secret: one-way crypto password, has
priority over ‘normal’ enable password
#config
terminal
#enable
secret <password>
Enable
password: password
to switch to priv mode
#config
terminal
#enable
password <password>
Virtual
terminal password: password
to allow telnet into router
#config
terminal
#line vty 0 <max number of
logins>
#login
#password
<whatever password>
Banner
#banner
motd <end Char>
yadda,
yadda, yadda <end Char>
Hostname
#config
t
#hostname
<router hostname>
hostname resolution
#ip
host <target hostname> <target host ip address>
this
acts like a host file to allow static name resolution
#show
hosts
displays
configured hosts / ip addresses
#ip
domain-lookup
#ip
name-server <dns ip>
to
configure DNS, use the 2 commands above.
You can have up to 6 dns addresses
#no
ip domain-lookup
disable
dns lookkup
Interface Naming
S Serial
E Ethernet
T TokenRing
F Fiddi
Number
as card/port or for 7000 series as VIP
card/port (from 0) /interface (from 0)
Static Routing for IP
Config
with:
#Ip
route <network> <mask> <address|interface> [distance]
Display
with:
#Show
ip route
#Show
ip route static
Remove
ip routes with:
#No
ip route <network>
Default
route / route of last resort : (set network and mask to all 0s)
#Ip route 0.0.0.0 0.0.0.0 <address>
IP
classless:
With IP classless ‘on’ packets are
forward on a best-guess directly connected network instead of having them
dropped.
-
this is used with default routes
Testing:
#ping
<address>
works
with IP, ipx, appletalk, apollo, vines, and decnet
#ping
<fill out info as prompted>
extended
ping: works with ip, appletalk, and ipx to provide much more info
#trace
<protocol> <address>
works
with: ip, appletalk, clns, oldvines (cisco), vines (banyan).
-
remember that TCP is not on any of these lists… it is a higher-level protocol.
Subinterfaces:
How
to bind multiple conflicting commands to 1 interface… use subinterfaces.
Syntax
is to place a period, then a integer after the device name.
Example: #int e0.100
Configuring
Dynamic Routing for IP
RIP:
#router
rip
#network
<network we want to advertise>
-optional
#passive <interface>
lets you run rip without
advertising connection
-optional #neighbor <specific
neighbor router>
lets info go over non-broadcast
media (like WAN links)
-optional
#debug ip rip or undebug ip rip
This
shows all updates to the console (sent or received advertisements)
-optional
#no router rip
Disables
rip routing
IGRP
#router
igrp <autonomous system number 1-65535>
turns
on igrp and allows setting of AS number
#network
<network we want to advertise>
-optional
#debug ip igrp events #undebug ip
igrp events
logs
to console when/what events are done
-optional#debug
ip igrp transactions #undebug ip igrp
transactions
detailed
log to console of what happens in each event
display
routing info:
#show
ip route
This
displays all routes on the router, including how the route was ‘learned’
R
= rip, C = connected, S = static, I = igrp, o = ospf, etc
#show
ip route <protocol>
displays
routes ‘learned’ from specified protocol only
#show
ip protocol
displays
protocol and detailed info on timing, sources of info, filters, etc.
#show
ip interface
shows
all lots of info on all interfaces
#show
ip interface <interface>
shows
info specific to the interface
IPX
configuration
#ipx
routing
to
enable ipx routing
#interface
<interface>
select
an interface before providing specifc info for configuring ipx
#ipx
network <ipx network address> [encapsulation <keyword for type>]
[secondary]
-
secondary indicates if more than one encapsulation type
is used on 1 interface, recomened to use sub-interfaces
table of info for configuring
encapsulation types
interface type frame type keyword
ethernet 802.3 novell-ether
(default)
802.2
sap
ethernet_II arpa
ethernet_snap snap
token
ring token-ring sap
(default)
token-ring_snap snap
fddi fddi_snap snap
(default)
802.2
sap
fddi_raw novell-fddi
Show
IPX servers
#show
ipx servers
this
displays the contents of the SAP, listing all servers and services
show
IPX route
#show
IPX route
shows
the IPX routing table
#ipx
maximum paths <2-512>
enable multiple
paths to 1 destination
#show
ipx traffic
generates
traffic statistics on ipx network usage
#show
ipx interface <interface>
detailed
info on specific interface
#debug
ipx <all kinds of things>
lots
of debug information available
Sources
for IOS software:
Flash
Memory
Default
and normally good idea
#show
flash
lists
all versions stored in flash, but does not specify which is running
#show
version
specifies
which version of IOS you are running currently
Tftp server
Somewhat
menu driven way to store and retrieve information to/from tftp server
#copy
flash tftp –lets you backup your ios saved in flash
#copy
tftp flash -lets you download new
versions or restore over bad versions
tftp
to backup / restore config info
#copy
tftp running-config
#copy
running-config tftp
Configuring
fallback sources for IOS software
#boot
system flash <ios_filename>
to boot from
flash
#boot
system tftp <ios_filename> <tftp_address>
to boot from
remote tftp server
#boot
system rom
to
boot from hard-coded ios version, this is a ‘last resort’ kinda thing to do
IOS
Commands that have little to do with routing
#show
version
os
version, uptime, how it was last started up, where ios was loaded from
hardware
type and revision as well as detected interfaces
#show
processes
shows pid, Queue priority, status
(TY), runtime in milliseconds, stack
space, proc name
#show
memory
shows
processor and I/O memory and watermarks / freespace
#show
stacks
shows
cause of last crash, and esoteric info
#show
buffers
reveals
size of buffers for small / middle / big / very big / large / huge
#show
flash
reveals
size and amount free, as well as what is stored.
#show
running-config
shows
the running configuration file
#show
startup-config
shows
the startup configuration file
#show
interface
shows
the hardware and their status, including usage stats
#show
interface <interface>
shows
hardware status and usage for specific interface
#show
protocol
shows
protocols enabled and routing info for each interface
#show
ip protocol
shows
more detail than show protocol
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