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Im!lement S!"nning #ree Protocols
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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!
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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
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)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.
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&ort Cost
Sum o& "ll the !ort costs "long the !"th to the root
bridge.
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)&*, &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.
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)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/
$%tended System I5 < Added to the bridge !riority v"lue.
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Configuring )ridge &riorit
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Configuring &ort &riorit
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&ort States
)loc!ing + #he !ort is " non+design"ted !ort "nd does not
!"rtici!"te in &r"me &or'"rding. -20 sec/
Listening + the s'itch !ort is not only receiving 4P5;
&r"mes, it is "lso tr"nsmitting its o'n 4P5; &r"mes-1
sec/
Learning + #he !ort !re!"res to !"rtici!"te in &r"me
&or'"rding "nd begins to !o!ul"te the AC "ddress t"ble. -1
sec/
3orwarding + #he !ort is considered !"rt o& the "ctive
to!ology "nd &or'"rds &r"mes "nd "lso sends "nd receives
4P5; &r"mes.
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Cisco &ort3ast %echnolog
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$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
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$ow the S%& Algorith# ,ses %hree Steps to
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$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(
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'4plain $ow the S%& Algorith# ,ses %hree
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'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
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+#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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