ip address and mac address

8/16/2019 IP Address and MAC Address

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The complete picture

Linux Network Management


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End to End Connection

• Being able to describe the end to endconnection sequence is a useful thing

• er! popular question on technicalinter"iews

• #suall! necessar! in troubleshooting $ %f !ou don&t know how it should work' !ou

won&t recogni(e problems when !ou seethem


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)TT* Connection

)ow do we google++


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,hat do we ha"e+++

• - name for the destination 1 google2com• 3ur own source %* address• 3ur own M-C address• 3ur own gatewa! %* address

• 3ur own 0N4 ser"er %* address• ,ell1known port addresses 5/etc/ser"ices6• 3ur own subnet mask


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-7* E8C)-N.E

what's your MAC?

00:C3:04:22:17:0A


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4tep 9 1 .et the router M-C

,e need to get the %* address of the name google2com

,e will get that from the 0N4 ser"er 5%* in resol"2conf64ince the %* address of the 0N4 ser"er is probabl! notlocal we need to send the 0N4 request to the router

:or that we need the M-C address of the router

Packet 1 Broadcast ARP request torouter port IP


8/21

4tep ; 1 -7* response

-ssuming the router port is up we will get an -7*response with the M-C of the router port

%: T)E7E %4 - *73BLEM ,E ,%LL 4EE - T7-CE,%T) 7E*E-TE0 -7* 7E


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0N4 L33=#*

who is google.com?

216.239. 1.100 DNS SERVER


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4tep > 1 0N4 7equest for

.oogle2com

Packet 3 DNS Query to DNS Ser er !inreso" #conf$ for %oo%"e#com

3ur 4ource %* and 4ource M-C

7andoml! generated 4ource *ort

0estination M-C is router port

0estination %* is the 0N4 ser"er

,ell known #0* 0N4 *ort ?>


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4tep @ 1 0N4 7esponse

Packet & DNS Response from DNSSer er 'it( IP of %oo%"e#com

0estination %* and 0estination M-C to us

#0* 0estination *ort same as 4ource in request

4ource M-C is router port4ource %* is the 0N4 ser"er

4ource #0* 0N4 *ort ?>


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TC* 4AN14AN/-C=1-C=

!"#

!"#$AC%

AC% WEB SERVER


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4tep ? 1 TC* 4AN

Packet ) *+P S,N to -**P Ser er

4ource M-C and %* from us

7andom TC* port

0estination M-C is router port0estination %* is the )TT* 4er"er

0estination )TT* *ort


14/21

4tep D 1 TC* 4AN/-C=

Packet . *+P S,N/A+0 from -**PSer er

0estination M-C and %* is to us

4ame TC* port we used in 4AN

4ource M-C is router port4ource %* is the )TT* 4er"er

4ource )TT* *ort


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4tep 1 TC* -C=

Packet *+P A+0 to -**P Ser er


4ame TC* port




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)TT* .ET 1 TC* -C=

& ( )*

C( AC%

WEB SERVER


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4tep 1 )TT* .ET

Packet -**P 4* to -**P Ser er


4ame TC* port



%t&s possible to ha"e the .ET with the -C= flag set

5*igg!1back -C=6


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4tep F 1 TC* -C=

Packet 5 *+P A+0 from -**P Ser er

0estination M-C and %* is to us

4ame TC* port we used in 4AN

4ource M-C is router port4ource %* is the )TT* 4er"er

4ource )TT* *ort


19/21

)TT* 7E4*3N4E 1 TC* -C=

& ( +*!(,#!*

C( AC% WEB SERVER


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4tep 9 1 )TT* 7E4*3N4E

Packet 16 -**P R4SP7NS4 from -**PSer er

0estination M-C and %* from us

4ame TC* port 5remember 1 socket pair defines TC*connection6

4ource M-C is router port

4ource %* is the )TT* 4er"er



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4tep 99 1 TC* -C=

Packet 11 *+P A+0 to -**P Ser er

4ource M-C and %* is from us

4ame TC* ports


4ource )TT* *ort

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