CISCO OSI networking modelx

calvesnorthNetworking and Communications

Oct 24, 2013 (3 years and 9 months ago)

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OSI networking model:


1. Physical layer (
bits
)




Electrical, mechanical, procedural, and functional specs, i.e. Ethernet, Token Ring,
etc.


2. Data Link layer (
frames
)




MAC (802.3), LLC (802.2), etc.


3. Network layer (
packets or datagrams
)




IP, etc.


4. Transport layer (
segments
)




TCP, UDP, etc.


5. Session layer (
data
)




NFS, SQL, RPC, X11, Appletalk session protocol, DNA SCP, etc.


6. Presentation layer




PICT, TIFF, JPEG, MPEG, etc.


7. Application layer




www, ftp, email, etc.




DDN/DOD networking model:


1. Network access layer




Equates to OSI Physical and Data Link layers


2. Internet layer




Equates to OSI Network layer


3. Host
-
to
-
Host layer




Equates to OSI Transport layer


4.
Process/Application layer




Equates to OSI Session, Presentation, and Application layers




Cisco's 3 layer networking model:


1. Core layer




Core of the network, high data rates, FDDI, ATM, Sonet, Fast Ethernet


2. Distribution layer




Workgrou
p layer, routing, filtering, separate broadcast domains, and WAN access


3. Access layer




Desktop layer, separate collision domains, hubs, switches




Subnetting:


Binary bits (big endian): 128 64 32 16 8 4 2 1




example:


1


0


0


0
0 0 0 1 = 129


Bits


Subnet


Hosts *


Wildcard (reversed!)


00000000 =


0


0


255


00000000 =


0


10000000 = 128


0


128


00000001 =


1


11000000 = 192


2


64


00000011 =


3


11100000 =

224


6


32


00000111 =


7


11110000 = 240


14


16


00001111 =


15


11111000 = 248


30


8


00011111 =


31


11111100 = 252


62


4


00111111 =


63


11111110 = 254


126


2


01111111 = 127


11111111 = 255



254


0


11111111 = 255


*


Routers can enable subnet zero to increase the host count by 1 (WARNING,


old BSD based UNIX systems use subnet 0 for broadcast!


If you have old BSD


systems on your network, do not enable subnet 0)


CIDR addressing
(RFC 1519, Introduction date: 1993)


The new (generally accepted around 1997 I

guess) way of showing network


address ranges is CIDR addressing (Classless Inter
-
Domain Routing) which


is written as a slash and a number, i.e. "/24".


The slash number
repres
ents


how many bits are in the netmask.


Thus, a /24 is 24 bits which is a


"classic"

Class C address space (the bits go from left to right [big
endian]).


CIDR: 11111111.11111111.11111111.00000000


mask:


255


.


255


.


255


.


0


range: x.x.x.0
-

x
.x.x.255


(remember, everything is octal so 2^8
-

1 is
255)


example: 10.0.0.0
-

10.0.0.255 (A "classic" Class C address space)


There are alot of weird address allocations now that CIDR is being


used (the old Class networks are no longer used for the mos
t part).


For instance, a company may have a /23 address space which is:


CIDR: 11111111.11111111.11111110.00000000


mask:


255


.


255


.


254


.


0


range: x.x.x.0
-

x.x.1.255


example: 10.0.0.0
-

10.0.1.255 (assuming the first subnet of /23)


A Cla
ss A network (/8, 255.0.0.0) can have 2^24
-

2 = 16,777,214 hosts


A Class B network (/16, 255.255.0.0) can have 2^16
-

2 = 65,534 hosts


A Class C network (/24, 255.255.255.0) can have 2^8
-

2 = 253 hosts


It's amazing how much address space is wasted.


I

once consulted at a


company that had a full Class A allocation, but only had around 80,000


computers in the entire company.


(They were also really stupid and put


live addresses on each desktop instead of using private address space


and NAT).





Calc
ulations:
256
-

netmask = subnetwork


example: 256
-

240 = 16 so subnetworks are: 0,


16,


32,


48,
etc.




broadcast are:


15,


31,


47,
etc.




host ranges are:


1
-
14,


17
-
30,


33
-
46,
etc.


Number of subnets:
2^x
-

2 where x = number of mask bits


example: mask of 192 is 2 bits, 2^2
-

2 = 2 subnets


Number of hosts:
2^x
-

2 where x = number of unmasked bits


example: mask of 192 is 6 unmasked bits 2^6
-

2 = 62




Cables


Pinout for a Cisco console cable is:
1
-
8, 2
-
7, 3
-
6, 4
-
5, 5
-
4, 6
-
3, 7
-
2, 8
-
1


(using RJ
-
45)(complete reverse).

Pinout for a T1 back to back:

1
-
5, 2
-
4, 4
-
2, 5
-
1


(using RJ
-
45)

Pinout of a T1 loopback:


1
-
5, 2
-
4
(using RJ
-
45)



MISC Notes:


-

Interfaces

are: type slot/port


-

802.2 frames have DSAP and SSAP fields

-

ATM uses 53 byte cells (hardware cell size + header)(payload is 48)(US wanted 64byte
payloads)

-

Gaint packet > 1518 bits

-

runt packet < 64 bits

-

Spanning tree is 802.1d

-

100baseT4 uses cat 3 or 4 cable

-

Class 1 repeater max allow delay is 140 bit times

-

Class 2 repeater max allow delay is 92 bit times (only supports 100baseTX and 100baseT4)

-

ports for companies: 255
-

1023


< Is this correct?


-

ports for public: 0

-
255


< Is this correct?


-

Arp entries last 4 hours in Cisco routers

-

802.3 Ethernet

-

802.5 Token Ring

-

802.3u


FastEthernet

-

802.3z/802.3ab


GigaEthernet

-

802.3ae 10 GigaEthernet

-

RIPv2 uses multicast to send routing infomation (2
24.0.0.9)

-

EIGRP and IGRP have default hop
-
count of 100

Administrative distance:


0


Directly connected interface

0


Static route pointing to an interface

1


Static route pointing to a next
-
hop neighbor

5


Summarized EIGRP

route

20


External BGP route

90


Internel EIGRP route

100


IGRP route

110


OSPF route

115


IS
-
IS route

120


RIP route

140


EGP route

170


External EIGRP route

200


Internal BGP route

255


Unknown routing source



SWITCHING:


VLAN 1 is the management VLAN, don't use it for switching!

Static VLAN:


Typical and most secure.


VLAN is statically assigned to the physical port and
never changes.

Dynamic VLAN:


VLAN Management Policy Server (VMPS) automatically assig
ns VLAN
based on MAC.

Two types of links in a switched environment: Access and Trunk links.

-


Access links:


Links that are only part of one VLAN.


VLAN information is removed from
frame before it goes out the port.

-


Trunk links: Trunks carry multipl
e VLANs.


Used to connect to other switches, routers, or
servers.



-

Two types of Trunk framing: ISL (Cisco only) and 802.1.q



-

Can carry 1 to 1005 VLANs

-

Frame tagging:


assignes user
-
defined ID to each frame, sometimes called a VLAN ID.

-


Frame types:


Inter
-
Switch Link (ISL) Fast Ethernet and GigaEthernet only.


Cisco Only



-

Adds a 26 byte header and a 4 byte FCS, can create a GIANT packet
(1522 bytes)



IEEE 802.1.q


IEEE standard



LAN emulation (LANE) used with ATM



802.10


used with FDDI

-

VLAN Trunk Protocol (VTP)



Server, client, and transparent server



Advertisements are sent every 5 minutes or whenever there
is a change



VTP pruning: Updates are onyl sent to devices on the VLAN that changed.


Off by
default.



CDP Cisco Discovery Protocol


Global or per interface



cdp enable



no cdp enable

Update every 60 sec (default) and hold down time is 180 sec

r2509#sh cdp nei


Capability Codes: R
-

Router, T
-

Trans Bridge, B
-

Source Route Bridge




S
-

Switch, H
-

Host, I
-

IGMP, r
-

Repeater


Device ID


Local Intrfce


Holdtme


Capability


Platform


Port ID


r2514


Eth 0


162


R


2500


Eth 0


r2504


Ser 1


175


R


2500


Ser 0


r2501


Eth 0


178


R


2500



Eth 0


r2509#sh cdp nei detail


-------------------------


Device ID: r2514


Entry address(es):




IP address: 10.0.0.14


Platform: cisco 2500,


Capabilities: Router


Interface: Ethernet0,


Port ID (outgoing port): Ethernet0


Holdtime : 124 sec


Versio
n :


Cisco Internetwork Operating System Software


IOS (tm) 2500 Software (C2500
-
JS
-
L), Version 11.2(17), RELEASE SOFTWARE (fc1)


Copyright (c) 1986
-
1999 by cisco Systems, Inc.


Compiled Mon 04
-
Jan
-
99 17:27 by ashah


-------------------------


Device ID: r
2504


Entry address(es):




IP address: 172.16.1.2


Platform: cisco 2500,


Capabilities: Router


Interface: Serial1,


Port ID (outgoing port): Serial0


--
<cut>
--






Novell/IPX


-

IPX


80bits
-

4 bytes for network, 6 bytes for node.


In Hex:




00007C80.0000.8609.33E9


7C80 is node address


-

SPX


Sequenced Packet Exchange


-

RIP


-

SAP


Service Advertisement Protocol


-

NLSP Netware Link Services Protocol


replaces RIP


-

NCP


Netware Core Protocol


-

GNS


Get NearestServer


(IPX broadcast) (u
sed by clients)


Ethernet_802.3


up to NW 3.11


Ethernet_802.2


since NW 3.12


Ethernet_II


supports both TCP/IP and IPX


Ethernet_SNAP


Appletalk, IPX, and TCP/IP


Interface


Novell frame type


Cisco Keyword


---------


----------
-------


--------------


Ethernet


Ethernet_802.3


novell
-
ether (default)




Ethernet_802.2


sap




Ethernet_II


arpa




Ethernet_snap


snap


Token Ring


Token
-
Ring



sap (default)




Token
-
Ring_snap


snap


FDDI


Fddi_snap


snap (default)




Fddi_802.2


sap




Fddi_raw


novell__fddi


IPX routing is easy:


r2509#conf t


r2509(
config)#ipx routing


r2509(config)#int e0


r2509(config
-
if)#ipx network 10


r2509(config
-
if)#int s1


r2509(config
-
if)#ipx network 10a


r2509(config
-
if)#end


r2509#sh ipx route


Codes: C
-

Connected primary network,


c
-

Connected secondary network





S
-

Static, F
-

Floating static, L
-

Local (internal), W
-

IPXWAN




R
-

RIP, E
-

EIGRP, N
-

NLSP, X
-

External, A
-

Aggregate




s
-

seconds, u
-

uses


2 Total IPX routes. Up to
1 parallel paths

and 16 hops allowed.


No default route known.


C


10 (NOVELL
-
ETHER),


Et0


C


10A (HDLC),


Se1


Note: "the 1 parallel paths".


To enable load balancing, enter




r2509(config)#ipx maximum
-
paths 2




To enable load balancing on a per host basis, enter:




r2509(config)#ipx per
-
ho
st
-
load
-
share


IPX subcommands:


r2509#sh ipx ?




access
-
lists


IPX access lists




accounting


The active IPX accounting database




cache


IPX fast
-
switching cache




compression


IPX compression information




eigrp


IPX EIGRP show
commands




interface


IPX interface status and configuration




nasi


Netware Asynchronous Services Interface status




nhrp


NHRP information




nlsp


Show NLSP information




route


IPX routing table




servers


SA
P servers




spx
-
protocol


Sequenced Packet Exchange protocol status




spx
-
spoof


SPX Spoofing table




traffic


IPX protocol statistics




ACCESS LIST


1
-
99


IP starndard


100
-
199


IP extended


200
-
299


Protocol type
-
code


300
-
399


DE
Cnet


400
-
499


XNS standard


500
-
599


XNS extended


600
-
699


Appletalk


700
-
799


48
-
bit MAC address


800
-
899


IPX standard


900
-
999


IPX extended


1000
-
1099


IPX SAP


1100
-
1199


Extended 48
-
bit


1200
-
1299


IPX summary address


IP extended can be based on IP proto, eigrp, gre, icmp, igmp, igrp, ip,
ipinip, nos, ospf, tcp, udp, ahp, esp




WAN


FR


Frame Relay


ISDN


Integrated Services Digial Network


LAPB


Link Access Procedure, Balanced


(used with X.25)


HDLC


High
-
level Da
ta Link Control (proprietary per vendor)


PPP


Point to Point Protocol




Layer 2


NCP




LCP




HDLC




Layer 1


EIA/TIA
-
232, V.24, V.35, ISDN


LMI


Local Mangement Interface.


Types: cisco, ansi, q933a


ISDN


NOTE: A U interface has a built in NT1, A S/T interface does not.


(some Sun computers
have a built in S/T.


Also, SGI Indy's have a S/T.)



North America uses U interface (2 wire).


Needs NT1 to convert to 4 wire
S/T




TE1 Terminal Equipment type 1.


Can plug right into ISDN network




TE2 Terminal Equipment type 2.


Older equipment, needs TA




NT1 Network Termination 1 implements the ISDN physical layer for user




NT2 Network Termination 2 is the provider's equipment, PBX, etc




TA


Terminal Adapte
r converts TE2 to TE1 wiring.




R reference point. Defines point between non
-
ISDN equipment (TE2) and TA.




S reference point. Defines point between customer's router and a NT2




T reference point. Defines point between NT1 and NT2.


S and T can be the
same.




U reference point. Defines point between NT1 and line
-
termination
equipment (NT2) (No TA/NT1 needed).




ITU Protocols: protocols beginning with:




E


deal with ISDN on existing network (POTS)




I


deal with concepts, aspects, services




Q


dea
l with switching and signaling




isdn q921


layer 2




isdn q931


layer 3