Exploration_LAN_Switching_Chapter5.ppt

© 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 1Version .0
Im!lement S!"nning #ree Protocols

© 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 2
Objectives
$%!l"in the role o& redund"ncy in " converged net'or(
Summ"ri)e ho' S#P 'or(s to elimin"te *"yer 2 loo!s in " converged net'or(
$%!l"in ho' the S#P "lgorithm uses three ste!s to converge on " loo!+&ree to!ology

Role of Redundanc in a Converged Switched Networ!

Laer " loops in a well #anaged networ!

© 2006 Cisco Systems, Inc. All rights reserved. Cisco Public

S%& Algorith# ( S#P uses the S!"nning #ree
Algorithm -S#A/ to determine 'hich s'itch !orts on " net'or( need to be con&igured &or bloc(ing to !revent loo!s &rom occurring.
Root )ridge + serves "s " re&erence !oint &or "ll s!"nning+tree c"lcul"tions to determine 'hich redund"nt !"ths to bloc(.
Root ports + S'itch !orts closest to the root bridge.
*esignated ports + All non+root !orts th"t "re still !ermitted to &or'"rd tr"&&ic on the net'or(

%he Root )ridge
A. Priority V"lue
C. AC Address

)est path to the root bridge
8hen the root bridge h"s been design"ted &or the s!"nning+tree inst"nce, the S#A st"rts the !rocess o& determining the best !"ths to the root bridge &rom "ll destin"tions in the bro"dc"st dom"in.

&ort Cost
Sum o& "ll the !ort costs "long the !"th to the root bridge.

)&*, &rocess
Initi"lly, e"ch s'itch identi&ies itsel& "s the root bridge.
$"ch s'itch m"int"ins loc"l in&orm"tion "bout its o'n 4I5, the root I5, "nd the !"th cost to the root.
8hen "d:"cent s'itches receive " 4P5; &r"me, they com!"re the root I5 &rom the 4P5; &r"me 'ith the loc"l root I5.

)ridge +*
4ridge Priority + #he s'itch 'ith the lo'est !riority, 'hich me"ns lo'est 4I5, becomes the root bridge -the lo'er the !riority v"lue, the higher the !riority/.
5e&"ult v"lue is 267 -1+66/
$%tended System I5 < Added to the bridge !riority v"lue.

Configuring )ridge &riorit
Configuring &ort &riorit

&ort States
)loc!ing + #he !ort is " non+design"ted !ort "nd does not !"rtici!"te in &r"me &or'"rding. -20 sec/
Listening + the s'itch !ort is not only receiving 4P5; &r"mes, it is "lso tr"nsmitting its o'n 4P5; &r"mes-1 sec/
Learning + #he !ort !re!"res to !"rtici!"te in &r"me &or'"rding "nd begins to !o!ul"te the AC "ddress t"ble. -1 sec/
3orwarding + #he !ort is considered !"rt o& the "ctive to!ology "nd &or'"rds &r"mes "nd "lso sends "nd receives 4P5; &r"mes.

Cisco &ort3ast %echnolog




$ow S%& wor!s to 'li#inate Laer " Loops in a Converged Networ! >ole o& S#P !ort st"tes "nd 4P5; timers in the
o!er"tion o& S#P
$ow the S%& Algorith# ,ses %hree Steps to

$ow the S%& Algorith# ,ses %hree Steps to
Converge on a Loop(3ree %opolog S#P decision se?uence is used to elect " root bridge
&or " net'or(
'4plain $ow the S%& Algorith# ,ses %hree

'4plain $ow the S%& Algorith# ,ses %hree
Steps to Converge on a Loop(3ree %opolog 5escribe the !rocess o& electing design"ted !orts "nd
non+design"ted !orts on " s'itch









© 2006 Cisco Systems, Inc. All rights reserved. Cisco Public
+#ple#ent Rapid per LAN Spanning %ree 6rapid &S%78 in a LAN 5escribe ho' to identi&y "nd solve the (ey S#P
con&igur"tion issues
Su##ar
S!"nning #ree Protocol -S#P/ is used to !revent loo!s &rom being &ormed on redund"nt net'or(s
S#P uses di&&erent !ort st"tes @ timers to logic"lly !revent loo!s
#here is "t le"st one s'itch in " net'or( th"t serves "s the root bridge
>oot bridge is elected using in&orm"tion &ound in 4P5; &r"mes

Su##ar
S#P lengthy convergence time -0 seconds/ &"cilit"ted the develo!ment o&3
>S#P
>"!id PVS#
is the !re&erred s!"nning+tree !rotocol on " Cisco s'itch
neto'r(

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Exploration_LAN_Switching_Chapter5.ppt

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