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8/2/2019 Spanning Tree Juniper
1/17
IMPLEMENTATION GUIDE
Ciht 2012, Juni Ntwks, Inc.
SpaNNINg Tree proToCol
IN layer2/layer 3
eNvIroNmeNTSCnfuin STp with Juni Ntwks
eX Sis ethnt Switchs
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IMPLEMENTATION GUIDE - Spanning Tree Protocol in Layer 2/Layer 3 Environments
Table o Contents
Intductin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Intductin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Snnin T ptc oiw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Th Juni Ntwks psitin n l 2 sus l 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Cniutin guid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Cniutin otins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
otin 1: l 2 ewh (Nt rcndd) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
STp/rSTp Cniutin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
mSTp Cniutin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
otin 2: l 3 t th C nd Btwn C nd atin ls; l 2 Btwn atin nd accss
ls nd t th accss l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
otin 3: l 3 ewh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Snnin T Intbiit with Cisc Switchs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
pvST+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Inttin STp/rSTp with pvST+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
muti Snnin T . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
vlaN Snnin T ptc (vSTp) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Cncusin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
abut Juni Ntwk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Table o Figures
Fiu 1: Cn Snnin-T instnc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Fiu 2: mSTp ws bth inks th ccss switch t b usd t th
s ti whi intinin - ntwk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Fiu 3: Tic th-ti ntis switchd ntwk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Fiu 4: pvST+ inttin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Fiu 5: Whn eX Sis switchs ci BpDUs Cisc switch, n th Ieee STp BpDU is
cssd; th pvST+ BpDUs dd s u unknwn l2 uticst ckts . . . . . . . . . . . . . . . . . . . . . . . 8
Fiu 6: Cisc t th c/tin s unnin pvST+ nd Juni Ntwks eX Sis
ethnt Switchs t th ccss unnin rSTp; n n ink is wdin tic . . . . . . . . . . . . . . . . . . . . . 9
Fiu 7: Juni Ntwks eX Sis ethnt Switchs t th c/tin s unnin rSTp nd
Cisc t th ccss unnin pvST+; n n uink n th Cisc switch is wdin tic . . . . . . . . . . .10
Fiu 8: CST is sti bsd n vlaN 1, n thuh th nti vlaN is 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2
Fiu 9: a switchs unnin mSTp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Fiu 10: vlaN d-bncin btwn pvST+ (c/tin switchs)
nd vSTp (ccss switch) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Fiu 11: BpDUs cid n th nti-n wi b ttd s u uticst ckt. . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
Fi u 1 2: T h u - t swi tc h is b ck in th du ndn t in k vl aN 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
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IMPLEMENTATION GUIDE - Spanning Tree Protocol in Layer 2/Layer 3 Environments
Introduction
This dcunt is ttd t Ses nd th tchnic udincs s n inttin uid cniuin th
Snnin T ptc (STp) with Juni Ntwks eX Sis ethnt Switchs.
Introduction
This inttin uid wi id bsic undstndin th sins th Snnin T ptc,
n 802.1d-1998, rSTp (802.1w) nd mSTp (802.1s), s w s bckund n cn ntis ntwks ndhw t d eX Sis switchs in ixd ninnt with Juni Ntwks mX Sis 3D Unis ed ruts
nd Cisc switchs.
Spanning Tree Protocol Overview
Th u-nd- Snnin T ptc (STp), l 2 tc tht nsus - t in bidd laNs, hs bn
und dcds. Snnin T-nbd switchs thuh t ctin css bsd n Bid ptc Dt Unit
(BpDU). a th switchs thn buid th shtst, wst-cst th t th t switch nd bck ts tht nt n ths
shtst ths, sutin in -, t-ik t. Withut tc such s Snnin T, l 2 bidd ntwks
susctib t bdcst/uticst nd/ unknwn unicst sts.
In th nxt w buts, w wi discuss th dint sins stndds-bsd STp, nd thn tk bi but
Ciscs Snnin T inttinp-vlaN Snnin T pus (pvST+):
Spanning Tree Protocol (STP802.1d 1998): Th iin sin STp (c STp) n suts sin instnc
Snnin T in bidd ntwk, tic d t s Cn Snnin T (CST). on 802.1Q tunks tht c uti
vlaNs, n vlaNusu th dut vlaN 1wi dictt th wdin t th vlaNs.
In STp, whn t is nbd th is n chn in th STp t, it cn tk u t 50 scnds
(maX_a + 2 x FWD_D, with dut tis) th bidd ntwk t cn.
Figure 1: Common Spanning-Tree instance
Rapid Spanning Tree Protocol (RSTP802.1w/802.1d 2004): Sii t c STp, rSTp ints sin
instnc Snnin T but dtic is th cnnc ti. F x, in c STp, hst t
cin nin cn tk u t 30 scnds (2 x FWD_D) b it bins wdin. Dict indict nd/ink
iu cnnc cn n tk u t 50 scnds (maX_a + 2 x FWD_D) with c STp. Such cnnc
tis nt cctb in tds hih-nc ntis ntwks.
rSTp cs sw cnnc tis b intducin nw t s (d t, tnt t nd bcku
t) nd nw cnnc bhi und sciic cnnctiit cnditins ( x, int-t-int shd
diu). Ths nhncnts nb rSTp t chi sub-scnd wdin nd ntwk cnnc. rSTp is
bckwd-ctib with c STp; i c STp BpDU is dtctd n ink, thn n rSTp-cb bid wi
t t c STp n tht in t.
Trunk
TrunkTrunk
Core/Aggregation
Access
Forwarding forall VLANs
Blocking forall VLANs
L2 Switch
L2 Switch
L2 Switch
Root Switch
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IMPLEMENTATION GUIDE - Spanning Tree Protocol in Layer 2/Layer 3 Environments
Multiple Spanning Tree Protocol (MSTP802.1s/802.1Q 2003): mSTp ws uti instncs Snnin T
t un cncunt bidd ntwk. a muti Snnin T Instnc (mSTI) is sscitd with u
vlaNs. Th cn b u t 64 mSTIs, nd ch instnc cn h its wn indndnt wdin t b
cniuin dint mSTI t switchs. This wi w inks n switchs t b utiizd. F x in Fiu
2, bth uinks th ccss switch wi b wdin tic instd just n s sn in c STp rSTp.
mSTp is n xtnsin rSTp tus (d ts, tnt ts nd s n) nd cn intt with STp/rSTp
switchs.
Per-VLAN Spanning Tree Plus/Rapid-PVST+ (PVST+/RPVST+): pvST+ is Ciscs sin Snnin T. In
pvST+, ch vlaN wi h its wn instnc Snnin T. on n 802.1Q tunk, vlaN 1 ws th c STp
(802.1d) stndd nd dtiss n th Ieee STp uticst, whs th th vlaNs n tunk ink dtis n
Ciscs sd uticst ddss. pvST+ hs th s cnnc ti s c STp.
Sinc pvST+ cnnc ti is sub-ti, Cisc inctd rSTp tus int pvST+, which th c rpvST.
Hw, rpvST+ sti dtiss n th sd uticst ddss vlaNs xct vlaN 1.
VLAN Spanning Tree Protocol (VSTP): vSTp is ctib with pvST+/rpvST+. Sii t pvST+/rpvST+, vSTp
cts -vlaN snnin t instnc vlaN cniud vSTp. vSTp BpDUs td with th
csndin vlaN idntii nd snt t uticst ddss 01-00-0C-CC-CC-CD t intct with Cisc pvST+/
rpvST+ bids. eX Sis switchs cn sut u t 128 vSTp instncs s Juns oS s 9.4r1.
Figure 2: MSTP allows both links o the access layer switch to be used at the
same time while maintaining a loop-ree network
The Juniper Networks Position on Layer 2 versus Layer 3
Th eX Sis cn b dd in ith l 2 l 3 ninnts, cbintin bth. This sctin
dscibs th dnts nd disdnts din l 3 sus l 2 sutins.
STp dds nth cxit t ntwk nnin nd tubshtin, cin ntwk dinistts t
cu chitct thi ntwks. Whn dinistts tskd with nnin l 2 ntwk, th knw
STp is ncss t nt l 2 s. Hw, th s c th chn dtinin which Snnin
T ptcSTp, rSTp mSTpt int, izin such dcisins qui tds btwn icinc/
unctinit nd siicit/cxit. F x, cnsid th dcisin hw t hnd tic wdin
dundnt inks: shud dinistts int mSTp, which is hih icint but cx, shud th us STp/
rSTp, which is ss icint but si t cniu?
Whn STp ds isbh du t us cniutin quint/stw iu, th cnsquncs cn b
dsttin. Bid s iht within th bidd ntwk, sutin in bdcst/uticst/unknwn-unicst
sts tht cn tk dwn th nti ntwk. Tubshtin such STp-td issus is n s tsk nd quis
STp xts t snd t d ti nwin dwn nd indin th t cus th iu.
Trunk
TrunkTrunk
Core/Aggregation
Access
Forwarding for Instance 1Blocking for Instance 2
Blocking for Instance 1Forwarding for Instance 2
L2 Switch L2 Switch
L2 Switch
Root Switch
for Instance 1
Root Switch
for Instance 2
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IMPLEMENTATION GUIDE - Spanning Tree Protocol in Layer 2/Layer 3 Environments
adinistts s nd t n dditin tus such s BpDU gud, rt gud l gud t nt
indtnt ntwk chns b u switchs. In dditin, t chi chnsi inttd hih ibiit (Ha)
in bth l 2 nd l 3, dinistts ust b cniznt th tinshi btwn utin tcs, vitu
rut rdundnc ptc (vrrp) nd STp.
Th eX Sis incuds u oSpF nd Ip uticst s t th bs stw icns, kin l 3 t th
ccss ib sutin nd iintin STp th tin nd c tins th ntwk. Ntwk
dinistts ust cu n Ip ctin in thi ntwk; in utd ntwk, dinistts shudnt
w but l 2 s bcus uinks shud b Ip sntd. N shud dinistts b cncnd but
unutiizd inks bcus oSpF ints qu-cst utith utin. Ntwk dinistts cn xct sub-
scnd cnnc with tus such s Bi-dictin Fwdin Dtctin (BFD) utin tc.
eiintin STp jit th ntwk ns tht th is n ss tc t n, tst, int,
tubsht nd n. Ntwk dinistts cn xct w cit nd tin xnss whn din
l 3 sutin with th eX Sis.
Confguration Guide
This sctin cs th th-tid c-, tin- nd ccss- tis cn usd in tds
ntis ntwk (s Fiu 3). Th Juni Ntwks duct ti cn b dd in th-tid ntwk.
at th c , instnc, ntwk chitcts dsi w-tnc switch with nn-bckin bics nd wi
t incdssutins such s Juni Ntwks mX Sis 3D Unis ed ruts. at th tin ,
dndin n th cnnctiit chic (10 gbe gbe), ith Juni Ntwks mX480 ethnt Sics rut
eX4200-24F (24-t 100/1000BaSe-X ib) switchs with vitu Chssis tchn cn b usd. at th ccss
, Juni Ntwks eX4200 in ethnt switchs ct it.
Figure 3: Typical three-tier enterprise switched network
Confguration Options
This sctin cs uti cniutin tins th t shwn in Fiu 3.
Option 1: Layer 2 Everywhere (Not Recommended)
as dscibd in th ius sctin, din Snnin T n th s is nt cndd du t th ddd
cxit. Hw, w wi sti c th cniutin s it is dd in s cust ntwks.
This sctin wi shw hw t cniu STp/rSTp nd mSTp n ch th switchs. Fist, th cnds
cniuin STp/rSTp n th switchs cd.
Core
Aggregation
Access
MX960-1 MX960-2
MX480
EX4200-1 EX4200-2 EX4200-3
EX4200
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IMPLEMENTATION GUIDE - Spanning Tree Protocol in Layer 2/Layer 3 Environments
STP/RSTP Confguration
Core Switches:
Sinc STp nd rSTp cniutins sii, this sctin wi cus n rSTp. T cniu STp, si chn th
kwd rSTp t STp.
In Snnin T, nbd Snnin T bids ist thuh t ctin css. Th switch with th wst
bid ID is dcd th t. a bid ID cnsists bid iit nd maC ddss. Th t switch is th bs
Snnin T wh th th nn-t switchs buid thi shtst th t th t switch nd bck n
dundnt inks. Th cnt th t switch is itnt sinc th jit tic wi ss thuh th t
switch.
rth thn n chnc, it is itnt t cniu th bid iit n th switch t k su tht it bcs
th t switch. Th bid iit duts t 32768 but is cniub 0 t 65536. I switchs h th s
bid iit, thn th bid with th wst maC ddss wins. In Fiu 3, th mX960-1 shud b th t switch,
sinc th jit cint tic wi b t nd th c nd/ t ss (tic s switchs nd/
WaN uts, nt shwn in th di, cnnctd t th c switchs). Th, mX960-1 is cniud with
bid-iit 4K (4096), which ks it th wst bid ID nd, cnsqunt, th t switch.
It is qu itnt t cniu bcku t switch. I t switch is, inin switchs t th
ctin css t sct nw t switch; cniuin bcku ws u t sct which dic wi tk in
th cs i iuin this cs, th c mX960-2 switch. Th, mX960-2 is cniud with bid-
iit 8K (8192), kin its bid ID hih thn mX960-1 but w thn th th switchs. This nsus tht it
bcs th nw t switch i th i t switch is.
juniper@MX960-1# set protocols rstp bridge-priority 4k
juniper@MX960-2# set protocols rstp bridge-priority 8k
Aggregation Switches:
Bcus rSTp t is d dsintd n th c switch, n xt rSTp cniutin is quid n th switchs in
th tin ; rSTp is nbd b dut n th eX Sis.
on th mX Sis ut, th s cnd s b (c ) is usd t nb rSTp, but withut th bid-
iit cnd.
Access Switches:
an ed pt tu ws t t tnsitin t wdin stt withut 30-scnd d (2 x FWD_D). This
tu is id ts tht cnnctd t pCs/ss, uts, iws nd s n.
rSTp uttic incts ed pt bsd n ctin chctistics t such s u-dux d nd
th ct tht n BpDU hs bn dtctd, but this tu hs th tin t b nu cniud n intc s
w. In th cs STp, th ed pt tu ust b nu cniud sciic intcs usin th win
cnd:
juniper@EX4200# set protocols stp interface ge-0/0/0.0 edge
I BpDU is dtctd n th ed pt, th tc is intint nuh t cssi th t s nn-d t. Thus
i is dtctd, th t cn tnsitin t bckin stt.
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IMPLEMENTATION GUIDE - Spanning Tree Protocol in Layer 2/Layer 3 Environments
MSTP Confguration
mSTp is th dsid Snnin T ptc. mSTp ws ntwk chitcts t d-bnc vlaNs, s w s t
ss tic thuh ths vlaNs uti uinks nd sti intin - ntwk. Whn cniuin mSTp,
th in n, isin in nd vlaN ins ust b th s n th switchs; thwis ths
switchs wi nt b t th s in. In th x shwn in Fiu 3, switchs in th ntis ntwk
in th s in.
Th jit ntis ntwks wi h n thn tw Snnin T instncs; ch mSTI wi b dt u vlaNs x, dd vlaNs Instnc 1 nd n vlaNs Instnc 2. T chi mSTI d
bncin, n th c switchs wi b th mSTI in t Instnc 1 nd th bcku mSTI in t
Instnc 2, nd ic s th th c switch.
Core Switches:
juniper@MX960-1# set protocols mstp msti 1 bridge-priority 4k vlan [v1 v3]
juniper@MX960-1# set protocols mstp msti 2 bridge-priority 8k vlan [v2 v4]
juniper@MX960-2# set protocols mstp msti 1 bridge-priority 8k vlan [v1 v3]
juniper@MX960-2# set protocols mstp msti 2 bridge-priority 4k vlan [v2 v4]
Aggregation and Access Switches:
juniper@MX480# set protocols mstp msti 1 vlan [v1 v3]juniper@MX480# set protocols mstp msti 2 vlan [v2 v4]
juniper@EX4200-1# set protocols mstp msti 1 vlan [v1 v3]
juniper@EX4200-1# set protocols mstp msti 2 vlan [v2 v4]
Dndin n t cnnctiit nd dnsit quints (10 gbe gbe), ith th mX480 ut th eX4200
switchs cn b usd t th tin .
Option 2: Layer 3 at the Core and Between Core and Aggregation Layers; Layer 2 Between Aggregation and
Access Layers and at the Access Layer
F this tin, oSpF th utin tcs ust b cniud t th c nd tin switchs. Sinc th
cus this dcunt is Snnin T, l 3 cniutins wi nt b cd.
F l 2, mSTp wud b id btwn th tin nd ccss s. Th t switch shud b n th tw
switchs in th tin . Sinc Snnin T cnds w cd in th ius sctin, n xs
wi b idd h.
Option 3: Layer 3 Everywhere
oSpF is t th bs icns ck th eX Sis; th, cniuin l 3 n uts/switchs in Fiu 3 is
nth tin. oSpF cniutins wi nt b cd, sinc th cus this dcunt is Snnin T.
en thuh l 3 is intd t th ccss , it is cndd tht Snnin T in nbd n th
eX Sis t nt indtnt s tht cn b cusd b nd uss.
Spanning Tree Interoperability with Cisco Switches
This sctin wi c STp intbiit btwn th Juni Ntwks eX Sis switchs nd Cisc switchs,
incudin th intctin btwn STp/rSTp nd pvST+. atnti sutins t pvST+ b usin mSTp (802.1s) wi
s b discussd.
PVST+
on in 802.1Q tunk, vlaN 1 BpDUs ws dtisd s untd t th w-knwn Ieee Snnin T
uticst ddss, 01:80:C2:00:00:00. Th th vlaN(s) n th tunk dtis td pvST+ BpDUs t Ciscs
sd uticst ddss, 01:00:0C:CC:CC:CD. This ws Cisc t h -vlaN instnc tht cn utiiz uti
dundnt tunk inks b d-bncin th vlaNs css th. as shwn in Fiu 4, dd vlaNs wdd n
n th uink tunks nd bckd n th th uink tunk, nd ic s th n vlaNs.
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IMPLEMENTATION GUIDE - Spanning Tree Protocol in Layer 2/Layer 3 Environments
on dwbck t pvST+ is tht it is nt bcd b n stndd. pvST+ s cs budn n switch
sucs such s CpU nd , s ch switch ust intin st STp dtbs instnc nd css
BpDUs n -t -vlaN bsis. Whi tht iht b oK with just w vlaNs, it bius cnnt sc whn
4,000 vlaNs sutd.
Figure 4: PVST+ implementation
Interoperating STP/RSTP with PVST+
B dut, rSTp is nbd n ethnt switchin-nbd ts n th eX Sis. rSTp bhs th s s STp,
s bth n int sin Snnin T instnc vlaNs tunk.
Cisc switchs, hw, dut t p-vlaN Snnin T pus (pvST+) tc.
B cntinuin, its itnt t undstnd hw th eX Sis intcts with th ius ts BpDUs th Cisc switchs
snd ut. Sinc Ieee STp BpDU is stndds-bsd nd dtiss t th w-knwn Ieee sd uticst ddss, th eX
Sis wi css th Ieee STp BpDU. Hw, sinc pvST+ BpDU is nn stndds-bsd tc nd dtiss t Ciscs
sd uticst ddss, th eX Sis wi tt it s n th uticst ckt nd d it n wdin ts within th
vlaN in which th scti BpDUs cid (s Fiu 5).
Figure 5: When EX Series switches receive BPDUs rom a Cisco switch, only the IEEE STP BPDU is
processed; the PVST+ BPDUs are looded as regular unknown L2 multicast packets
Trunk
TrunkTrunk
Core/Aggregation
Access
Forwarding for Odd VLANsBlocking for Even VLANs
Forwarding for Even VLANsBlocking for Odd VLANs
L2 Switch L2 Switch
L2 Switch
Switch 1Root for Odd VLANs
Switch 3
Switch 2Root for Even VLANs
01:80:C2:00:00:00 Cisco SRC MAC BPDU VLAN 1
01:00:0C:CC:CC:CD
01:00:0C:CC:CC:CD
Cisco SRC MAC 1Q Tag
1Q Tag
BPDU VLAN 2
Cisco SRC MAC BPDU VLAN n
IEEE BPDUs on VLAN1re-generated be EX Series Switch
PVST+BPDUs on VLAN2/VLAN3originally sent by Cisco switch
TrunkonlyVL
ANs
1and2
Trunk all VLANs Trunk all VLANs
Cisco Switch
Juniper NetworksEX Series Switch
STP Databasege-0/0/0 FWDge-0/0/1 FWDge-0/0/2 FWD
PVST + BPDUs
L2 Switch L2 Switch
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IMPLEMENTATION GUIDE - Spanning Tree Protocol in Layer 2/Layer 3 Environments
Nw tht its undstd hw eX Sis switchs hnd th ius ts BpDUs tht Cisc switchs snd ut, th
nxt st wi b t s hw tic l 2 t wdin th wi bh with ixtu Juni Ntwks
switchs unnin STp/rSTp nd Cisc switchs unnin pvST+.
In Fiu 6, vlaNs 1 thuh 4 tsin 802.1Q tunk inks. Switchs 1 nd 2 Cisc switchs unnin pvST+.
Switch 1 is th STp t vlaNs 1 nd 3 with bid iit 4096. It is s th STp bcku t switch
vlaNs 2 nd 4 with bid iit 8192. Switch 2 is th STp t switch vlaNs 2 nd 4 with bid iit
4096 nd is th STp bcku t switch vlaNs 1 nd 3 with bid iit 8192.
Th is n dditin ct t pvST+. B dut, th th cst ssind b pvST+ is bsd n Ciscs STp cst
cnntin, nt th Ieee STp cst. Th, th th cst nds t b chnd s tht it cis with Ieee STp
th cst nd sii inks (ik Fste, gbe) h th s ink-cst u. on th Cisc dics, th cnd
snnin-t thcst thd n ust b ntd t k it cint with Ieee STp th cst. This cnd
wi b id t Cisc switch ts.
Switch 3 in Fiu 6 is Juni Ntwks eX Sis switch unnin rSTp. Sinc rSTp n hs sin Snnin T
instnc vlaNs css tunk nd th is n vlaN wnss, tic wi b wdd bckd bsd
n th vlaN 1 t. Th, th ink btwn Switch 1 nd Switch 3 wi b wdin all vlaNs (vlaN 1
thuh 4) nd th th ink wi b bckin all vlaNs (vlaN 1 thuh 4).
Th nt sut is tht Switch 3 is bckin n th uinks; th is n ic l2 in th t sntd in
Fiu 6, dss which Cisc switch is th t n th vlaNs (xct vlaN 1) nd dss th ct
tht ths Cisc switchs unnin pvST+.
Figure 6: Cisco at the core/aggregation layers runnin g PVST+ and Juniper Networks EX Series
Ethernet Switches at the access layer running RSTP; only one link is orwarding traic
Th utut bw is tkn Switch 3. F th shw snnin-t bid cnd, th eX Sis switch
cknwdd th t bid is Switch 1. Th shw snnin-t intc cnd shws th t stts
nd, bsd n th utut, n intc -0/0/0.0 is wdin.
Trunk
TrunkTrunk
Core/Aggregation
Access
Blocking forall VLANs
L2 Switch L2 Switch
L2 Switch
Switch 1Root for Odd VLANs00:1b:d5:8a:0a:00
Switch 2Root for Even VLANs
00:1b:d4:ce:c4:00
Switch 300:19:e2:50:63:a0
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IMPLEMENTATION GUIDE - Spanning Tree Protocol in Layer 2/Layer 3 Environments
juniper@EX4200> show spanning-tree bridge
STP bridge parameters
Context ID : 0
Enabled protocol : RSTP
Root ID : 4097.00:1b:d5:8a:0a:00
Root cost : 20000
Root port : ge-0/0/0.0
Hello time : 2 secondsMaximum age : 20 seconds
Forward delay : 15 seconds
Message age : 1
Number of topology changes : 6
Time since last topology change : 315 seconds
Local parameters
Bridge ID : 32768.00:19:e2:50:63:a0
Extended system ID : 0
Internal instance ID : 0
juniper@EX4200> show spanning-tree interface
Spanning tree interface parameters for instance 0
Interface Port ID Designated Designated Port State Role
port ID bridge ID Cost
ge-0/0/0.0 128:514 128:1 4097.001bd58a0a00 20000 FWD ROOT
ge-0/0/1.0 128:516 128:55 8192.001bd4cec400 20000 BLK ALT
In Fiu 7, th t hs bn sd, with th eX Sis t th c/tin s nd th Cisc switch t
th ccss , sutin u vlaNs.
Figure 7: Juniper Networks EX Series Ethernet Switches at the core/aggregation layers running RSTP
and Cisco at the access layer running PVST+; only one uplink on the Cisco switch is orwarding traic
Trunk
TrunkTrunk
Core/Aggregation
Access
Blocking forall VLANs
L2 Switch L2 Switch
L2 Switch
Switch 1Root
00:19:e2:50:63:a0
Switch 2
00:19:e2:50:93:60
Switch 300:1b:d5:8a:0a:00
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IMPLEMENTATION GUIDE - Spanning Tree Protocol in Layer 2/Layer 3 Environments
ain, rSTp is nbd n th eX Sis (Switchs 1 nd 2) nd pvST+ is nbd n th Cisc switch (Switch 3). Switch 1 is th
t th CST with iit 4096; Switch 2 is th bcku t switch th CST with iit 8192.
Switch 3 (th Cisc switch unnin pvST+) cnizs Switch 1 s th STp t vlaN 1 nd cnizs Switch 2 s
hin w bid-iit thn its n vlaN 1, th bckin its uink tunk t t Switch 2 n vlaN 1.
F vlaNs 2-4, Switch 3 snds ut Cisc pvST+ BpDUs n th tunks. Bcus Switch 1 nd Switch 2 d nt
undstnd pvST+ BDpUs, th switchs wi tt th s u l2 uticst ckts nd d th. Switch 3 is th
pvST+ t vlaNs 2-4 nd cis its wn pvST+ BpDUs n vlaNs 2-4 n bth its uinks; it nds u bckinn ths tw uink tunk ts.
Th, th sut is wdin t sii t tht in Fiu 6, in with n n tunk-t uink
wdin n vlaNs n Switch 3 nd th th uink tunk t bckin n vlaNs. Fwin is th utut
th Cisc switch (Switch 3) shwin th t Fiu 7. Ntic th w tht th vlaNs bckin
n gi1/0/2. as, nt tht th t vlaN 1 is dint th th vlaNs; n vlaN 1, it is cssiid s n
tnt t whi n th th vlaNs, it is cssiid s bcku, indictin tht Switch 3 cis its wn BpDUs n
ths vlaNs n t gi1/0/2.
3750E#show spanning-tree
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 4096
Address 0019.e250.63a0Cost 20000
Port 14 (GigabitEthernet1/0/14)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 001b.d58a.0a00
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- -------------------------------
Gi1/0/1 Root FWD 20000 128.13 P2p
Gi1/0/2 Altn BLK 20000 128.14 P2p
VLAN0002
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- -------------------------------
Gi1/0/1 Desg FWD 20000 128.13 P2p
Gi1/0/2 Back BLK 20000 128.14 P2p
VLAN0003
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- -------------------------------
Gi1/0/1 Desg FWD 20000 128.13 P2p
Gi1/0/2 Back BLK 20000 128.14 P2p
VLAN0004
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- -------------------------------
Gi1/0/1 Desg FWD 20000 128.13 P2p
Gi1/0/2 Back BLK 20000 128.14 P2p
as nt tht n th Cisc switch, whn chnin th nti vlaN ID tunk t sthin th thn vlaN 1, th
CST t is sti bsd n vlaN 1; this is bcus th Cisc dic wi sti snd th Ieee STp BpDUs untd
with vlaN 1 ts n 802.1Q tunk. and th vlaN ID tht is dcd s nti-n, th Cisc switch wi
snd n untd pvST+ BpDU t th Cisc s uticst maC ddss 01:00:0C:CC:CC:CD.
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In Fiu 8 bw, vlaN 2 is th nti vlaN btwn Cisc nd Juni Ntwks. Th Ieee STp BpDU snt b th
Cisc switch sti cntins vlaN 1 ts nd is untd. as nt tht th BpDU vlaN 2 is sti snt n th
pvST+ uticst ddss b th Cisc switch nd is untd.
ps nt: It is iti t tch th nti vlaN ID n bth sids n 802.1Q tunk.
Figure 8: CST is still based on VLAN 1, even though the native VLAN is 2
Multiple Spanning Tree
mSTp hs c ths STp/rSTp shtcins, s w s itit th dndin suc quints nd
ck stndds cinc tht sscitd with pvST+. Th bnit mSTp is its biit t u
vlaNs t muti Snnin T Instnc th thn just n vlaN instnc s sn with pvST+. Dint t
switchs nd dint STp ts cn b cniud ch mSTI, sutin in dint l 2 wdin
t. F x, s shwn in Fiu 4, thuh th cud b n vlaNs cniud btwn th ccss nd
c/tin s n ntis ntwk, th jit ths ntwks h n thn tw Snnin T
wdin tis. Hnc, instd intinin X instncs STp X nub vlaNs und pvST+, it n
tks tw mSTIs t chi th s sut with mSTph th vlaNs d t mSTI 1 nd h th vlaNs d
t mSTI 2, s shwn in Fiu 9. I th ntwk dinistt dsis dditin Snnin T tis, mSTIs
cn b ddd (u t xiu 64).
Th quid mSTp cniutins eX Sis nd Cisc switchs shwn in Fiu 9 idd bw. Nt tht
switchs in th s mSTp in, nd th t switchs ch mSTI n th c switchs.
Figure 9: All switches running MSTP
01:80:C2:00:00:00 Cisco SRC MAC BPDU VLAN 1
01:00:0C:CC:CC:CD
01:00:0C:CC:CC:CD
Cisco SRC MAC
1Q Tag
BPDU VLAN 2
Cisco SRC MAC BPDU VLAN n
PVST+BPDUs on VLAN2/VLAN3originally sent by Cisco switch
TrunkonlyVLANs
1and2
Trunk all VLANs
Native VLAN is 2
Trunk all VLANs
Cisco Switch
Juniper NetworksEX Series Switch
STP Databasege-0/0/0 FWDge-0/0/1 FWD
ge-0/0/2 FWD
PVST + BPDUs
L2 Switch L2 Switch
IEEE BPDUs on VLAN1re-generated be EX Series Switch
Trunk
TrunkTrunk
Core/Aggregation
Access
Forwarding for Instance 1Blocking for Instance 2
Blocking for Instance 1Forwarding for Instance 2
L2 Switch L2 Switch
L2 Switch
Switch 1Root for Instance 1
Switch 2Root for Instance 2
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Switch 1, Cisc switch, hs th win cniutin:
3750E-1(confg)#spanning-tree mode mst
3750E-1(confg)#spanning-tree mst 0,1 priority 4096
3750E-1(confg)#spanning-tree mst confguration
3750E-1(confg-mst)#instance 1 vlan 1,3
3750E-1(confg-mst)#instance 2 vlan 2,4
Th utut bw idts th cniutins shwn b. Switch 1 is t mST0 nd mST1 bcus th th cst
is 0 nd th is n t t, whs th mST2 t is Switch 2.
3750E-1#show spanning-tree root
Root Hello Max Fwd
MST Instance Root ID Cost Time Age Dly Root Port
---------------- -------------------- --------- ----- --- --- ------------
MST0 4096 001b.d58a.0a00 0 2 20 15
MST1 4097 001b.d58a.0a00 0 2 20 15
MST2 4098 001b.d4ce.c400 20000 2 20 15 Gi1/0/2
Switch 2, s Cisc switch, hs th win cniutin:
3750E-2(confg)#spanning-tree mode mst
3750E-2(confg)#spanning-tree mst 2 priority 4096
3750E-2(confg)#spanning-tree mst confguration
3750E-2(confg-mst)#instance 1 vlan 1,3
3750E-2(confg-mst)#instance 2 vlan 2,4
Th utut bw idts th cniutins shwn b. Switch 2 is t mST2 bcus th th cst is 0 nd
th is n t t, whs Switch 1 is t mST1 nd mST0.
3750E-2#show spanning-tree root
Root Hello Max Fwd
MST Instance Root ID Cost Time Age Dly Root Port---------------- -------------------- --------- ----- --- --- ------------
MST0 4096 001b.d58a.0a00 0 2 20 15 Gi2/0/2
MST1 4097 001b.d58a.0a00 20000 2 20 15 Gi2/0/2
MST2 4098 001b.d4ce.c400 0 2 20 15
Switch 3, Juni Ntwks eX Sis switch, hs th win cniutin:
juniper@EX4200# set protocols mstp msti 1 vlan [v1 v3]
juniper@EX4200# set protocols mstp msti 2 vlan [v2 v4]
Th utut bw shws tht bth inks n th eX Sis switchs bin utiizd. Th ink btwn Switch 1 nd
Switch 3 is wdin mSTI 1 nd bckin mSTI 2; th ink btwn Switch 2 nd Switch 3 is wdin mSTI
2 nd bckin mSTI 1.
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juniper@EX4200> show spanning-tree interface
Spanning tree interface parameters for instance 0
Interface Port ID Designated Designated Port State Role
port ID bridge ID Cost
ge-0/0/2.0 128:515 128:1 4096.001bd58a0a00 200000000 FWD ROOT
ge-0/0/3.0 128:516 128:55 32768.001bd4cec400 200000000 BLK ALT
Spanning tree interface parameters for instance 1
Interface Port ID Designated Designated Port State Role
port ID bridge ID Cost
ge-0/0/2.0 128:515 128:1 4097.001bd58a0a00 200000000 FWD ROOT
ge-0/0/3.0 128:516 128:55 32769.001bd4cec400 200000000 BLK ALT
Spanning tree interface parameters for instance 2
Interface Port ID Designated Designated Port State Role
port ID bridge ID Cost
ge-0/0/2.0 128:515 128:1 32770.001bd58a0a00 200000000 BLK ALT
ge-0/0/3.0 128:516 128:55 4098.001bd4cec400 200000000 FWD ROOT
VLAN Spanning Tree Protocol (VSTP)
vSTp, intducd in Juns oS 9.4r1 th eX3200 nd eX4200 switchs, ws uss t ct st snnin-
t instncs vlaN cniud ( s Fiu 10). vSTp BpDUs tnsittd s td ckts t
uticst dstintin maC ddss 01-00-0C-CC-CC-CD n 802.1Q tunkd ts. on th ccss t, vSTp BpDUs
snt t th Ieee w-knwn uticst maC ddss (01-80-C2-00-00-00) with th csndin snnin-t
intin th vlaN t which th ccss t bns.
vSTp is quint t Ciscs rpvST+ but is bckwd-ctib with Ciscs pvST+. B dut, vSTp BpDUs
quint t rpvST+ ( dtid dscitin pvST+/rpvST+, s iw th Snnin T oiw
sctin). Hw, i th djcnt switch is sndin pvST+ BpDUs, thn th eX Sis switch wi snd th vSTp BpDU
quint t pvST+ BpDUs bckwd ctibiit.
Figure 10: VLAN load-balancing between PVST+ (core/aggregation switches)
and VSTP (access switch)
Core/Aggregation
Access
Blocking for Even VLANsForwarding for Odd VLANs
Forwarding for Even VLANsBlocking for Odd VLANs
Switch 3
Switch 1Root for Odd VLANs
Switch 2Root for Even VLANs
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IMPLEMENTATION GUIDE - Spanning Tree Protocol in Layer 2/Layer 3 Environments
Whn th laN instuctu incuds ix Juni nd Cisc switchs nd is cniud -vlaN snnin-
t, it is cndd tht th snnin-t d n th Cisc switchs b chnd pvST+ t rpvST+.
pvST+ ds nt h th s st cnnc tus (tst, uinkst nd bckbnst) tht nti
buit int rpvST+.
on n snnin- t tc cn b cti n n eX Sis switch t n in ti. T nb vSTp n th eX
Sis switchs, rSTp-td cniutins ust ist ith b dtd dctitd. Thn, th win sntx
nds t b intd n vlaN tht nds t b cniud vSTp:
st tcs st n
Bid ii t, t iit nd t cst cniud und th vlaN th vSTp tc. vSTp/pvST+ Ieee
BpDUs wi nt b cssd, ntd dd n vlaN tht is nt cniud und vSTp.
Bw is s cniutin nbin vSTp n eX Sis switchs. In this x th i vlaNs,
thuh n vlaNs 2-5 cniud vSTp. This dcunt wi discuss vlaN 1 in th nxt cu hs.
juniper@EX4200> show confguration protocols
vstp {
vlan 2;
vlan 3;
vlan 4;
vlan 5;}
Bs n th t in Fiu 10 nd th b cniutin, th win utut cn b xctd n th eX Sis
switchs:
juniper@EX4200> show spanning-tree interface
Spanning tree interface parameters for VLAN 2
Interface Port ID Designated Designated Port State Role
port ID bridge ID Cost
ge-0/0/2.0 128:515 128:1 4098.001bd58a0a00 200000000 FWD ROOT
ge-0/0/3.0 128:516 128:55 32770.001bd4cec400 200000000 BLK ALT
Spanning tree interface parameters for VLAN 3
Interface Port ID Designated Designated Port State Role
port ID bridge ID Cost
ge-0/0/2.0 128:515 128:1 32771.001bd58a0a00 200000000 BLK ALT
ge-0/0/3.0 128:516 128:55 4099.001bd4cec400 200000000 FWD ROOT
Spanning tree interface parameters for VLAN 4
Interface Port ID Designated Designated Port State Role
port ID bridge ID Cost
ge-0/0/2.0 128:515 128:1 4100.001bd58a0a00 200000000 FWD ROOT
ge-0/0/3.0 128:516 128:55 32772.001bd4cec400 200000000 BLK ALT
Spanning tree interface parameters for VLAN 5
Interface Port ID Designated Designated Port State Role
port ID bridge ID Cost
ge-0/0/2.0 128:515 128:1 32773.001bd58a0a00 200000000 BLK ALT
ge-0/0/3.0 128:516 128:55 4101.001bd4cec400 200000000 FWD ROOT
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F th b utut, nt th is snnin- t instnc ch vlaN cniud vSTp. Th wdin nd
bckin inks tch Fiu 10; dd-nubd vlaNs bckin n -0/0/2.0 nd wdin -0/0/3.0 nd ic
s th n-nubd vlaNs.
Th w thins but Juns oS 9.4 wth ntinin:
vSTp is sutd n th eX3200 nd eX4200 ins switchs n. Th eX8200 in wi su t vSTp in
utu s.
Th nub su td vSTp instncs in 9.4r1 is 128. This nub wi b incsd t 253 in 9.4r2.
eX Sis switchs wi nt css Ieee BpDUs with Cisc switchs n vlaN 1 (s d bw dtis).
This wi b sutd in utu s.
With Cisc switchs, vlaN 1 cis with th Ieee snnin-t sciictin. Cunt th eX Sis switchs
cnnt css BpDUs n vlaN 1 with Cisc switchs. I th is tunk t cniud btwn Cisc switchs nd
Juni eX Sis switchs, thn th vlaN tht is cniud s th nti-n thn tht vlaN (nti-n) wi tt
th BpDUs s u uticst nd d th BpDU (s Fiu 11). Th, th eX Sis switchs wi n
th switchs t bck th dundnt inks (s Fiu 12).
Figure 11: BPDUs received on the native-vlan will be treated as regular multicast packet.
Figure 12: The upper-let switch is blocking the redundant link or VLAN 1.
Root for VLANs 1-X
Trunk
native-vlan 1
Trunk
native-vlan1
vlan=X
access
vlan=X
access
vlan=X
access
VLAN 1 notconfiguredfor VSTP
EX Series
IEEEBPDU
IEEEBPDU
IEEE
BPDU VSTP
BPDU802.1Q=2
802.1Q=XVSTPBPDU
Core/Aggregation
Access
All trunks carrying all VLANsand the native-vlan is 1
EX Series
Root for VLANs 1 and 2Backup Root for VLANs 3 and 4
Root for VLANs 3 and 4Backup Root for VLANs 1 and 2
Blocking for VLAN 1
Blocking for VLAN 2Blocking for VLANs 3 and 4
Trunk
TrunkTrunk
PVST+
VLAN 1 notconfiguredfor VSTP
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8010002-004-EN Jan 2012
Copyright 2012 Juniper Networks, Inc. All rights reserved. Juniper Networks, the Juniper Networks logo, Junos,
NetScreen, and ScreenOS are registered trademarks of Juniper Networks, Inc. in the United States and other
countries. All other trademarks, service marks, registered marks, or registered service marks are the property of
their respective owners. Juniper Networks assumes no responsibility for any inaccuracies in this document. Juniper
Networks reserves the right to change, modify, transfer, or otherwise revise this publication without notice.
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Phone: 35.31.8903.600
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Phone: 888.JUNIPER (888.586.4737)
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authorized reseller.
pintd n ccd
Conclusion
Juni Ntwks eX Sis ethnt Switchs cn b dd in ith l 2 l 3 ninnt. Hw, i l 2
t is ust, thn th Snnin T ptc is ncss t nt n unwntd l2 bid s. This inttin
uid hs cd th undnts nd cniutins th stndds-bsd Snnin T ptcs. B win
ths uidins, Juni custs cn cnidnt intt eX Sis switchs int thi cunt ntwk instuctu withut
cisin dsid STp stbiit, unctinit nd xibiit.
About Juniper Network
Juni Ntwks is in th businss ntwk inntin. F dics t dt cnts, cnsus t cud
ids, Juni Ntwks dis th stw, siicn nd ssts tht tns th xinc nd cnics
ntwkin. Th cn ss custs nd tns wdwid. additin intin cn b und t
www.juniper.net.