Multiple Spanning Tree (MST)

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Nedjelja, 06 Juni 2010 13:58

Podrazumijevani režim spanning tree protokola na Cisco Catalyst switchevima je PVST+ ili, na novijim modelima, Rapid PVST+. Pomenute varijante protokola imaju za rezultat direktno, jedan na jedan mapiranje spanning tree instanci u VLAN-ovima. Na primjer, ako imamo osam VLAN-ova na switchu, taj switch mora učestvovati u osam nezavisnih spanning tree instanci. Ovo je veoma često nepoželjno rješenje, zbog toga što je broj jedinstvenih spanning tree topologija najčešće manji od broja VLAN-ova(u najgorem slučaju, taj broj će biti jednak). Pokretanje samo jednog "common spanning tree" režima(CST, Cisco Catalyst switchevi ga ne podržavaju) bi bilo mnogo djelotvornije, ali nam taj režim ne dozvoljava fleksibilnost unutar dizajna koju možemo pronaći kod PVST-a.

Multiple Spanning Tree (MST) je napravljen da bi nam dozvolio korištenje višestrukih spanning tree topologija uz istovremeno održavanje skalabilnosti. MST omogučava administratoru mapiranje proizvoljnog broja VLAN-ova u jedinstvenu MST instancu, što će rezultirati minimalnim brojem potrebnih instanci da bi se zadovoljio dizajn. Ako, na primjer, imate šest VLAN-ova a samo dvije jedistvene topologije drugog sloja(L2), bće vam potrebne samo dvije MST instance.

MST konfiguracija

Donja topologija ilustrira uobičajen scenario u kojem switch drugog sloja(L2) nosi četiri VLAN-a i ima dva uplinka prema dva distribucijska swictha. Rutirani SVIs sa HSRP je konfigurisan na distribucijskim switchevima da bi nam obezbjedio redundantne defaultne gateway-e za korisnike u sva četiri VLAN-a.

Ovo je osnovna konfiguracija za svako od tri switcha.

Osnovna konfiguracija

S1

vlan 10
vlan 20
vlan 30
vlan 40
!
interface FastEthernet0/13
 switchport trunk encapsulation dot1q
 switchport mode trunk
!
interface FastEthernet0/16
 switchport trunk encapsulation dot1q
 switchport mode trunk
!
interface Vlan10
 ip address 192.168.10.1 255.255.255.0
 standby 10 ip 192.168.10.3
 standby 10 priority 110
 standby 10 preempt
 standby 10 track FastEthernet0/13 20
!
interface Vlan20
 ip address 192.168.20.1 255.255.255.0
 standby 20 ip 192.168.20.3
!
interface Vlan30
 ip address 192.168.30.1 255.255.255.0
 standby 30 ip 192.168.30.3
 standby 30 priority 110
 standby 30 preempt
 standby 30 track FastEthernet0/13 20
!
interface Vlan40
 ip address 192.168.40.1 255.255.255.0
 standby 40 ip 192.168.40.3

S2

vlan 10
vlan 20
vlan 30
vlan 40
!
interface FastEthernet0/13
 switchport trunk encapsulation dot1q
 switchport mode trunk
!
interface FastEthernet0/16
 switchport trunk encapsulation dot1q
 switchport mode trunk
!
interface Vlan10
 ip address 192.168.10.2 255.255.255.0
 standby 10 ip 192.168.10.3
!
interface Vlan20
 ip address 192.168.20.2 255.255.255.0
 standby 20 ip 192.168.20.3
 standby 20 priority 110
 standby 20 preempt
 standby 20 track FastEthernet0/13 20
!
interface Vlan30
 ip address 192.168.30.2 255.255.255.0
 standby 30 ip 192.168.30.3
!
interface Vlan40
 ip address 192.168.40.2 255.255.255.0
 standby 40 ip 192.168.40.3
 standby 40 priority 110
 standby 40 preempt
 standby 40 track FastEthernet0/13 20

S3

vlan 10
vlan 20
vlan 30
vlan 40
!
interface FastEthernet0/13
 switchport trunk encapsulation dot1q
 switchport mode trunk
!
interface FastEthernet0/16
 switchport trunk encapsulation dot1q
 switchport mode trunk

Na S3, access portovi se trebaju podijeliti po VLAN-ovima.

Možemo vidjeti da se po defaultu kreira PVST+ instanca automatski za svaki VLAN:

S1# show spanning-tree summary
Switch is in pvst mode
Root bridge for: none
Extended system ID           is enabled
Portfast Default             is disabled
PortFast BPDU Guard Default  is disabled
Portfast BPDU Filter Default is disabled
Loopguard Default            is disabled
EtherChannel misconfig guard is enabled
UplinkFast                   is disabled
BackboneFast                 is disabled
Configured Pathcost method used is short

Name                   Blocking Listening Learning Forwarding STP Active
---------------------- -------- --------- -------- ---------- ----------
VLAN0001                     1         0        0          1          2
VLAN0010                     1         0        0          1          2
VLAN0020                     1         0        0          1          2
VLAN0030                     1         0        0          1          2
VLAN0040                     1         0        0          1          2
---------------------- -------- --------- -------- ---------- ----------
5 vlans                      5         0        0          5         10

MST konfiguracija

Potrebno je konfigurisati dvije MST instance na svakom od tri switcha, koje će biti nosici dva access VLAN-a. Ovo se radi u MST configuration režimu. Svi VLAN-ovi se dodjeljuju MST instanci 0 po defaultu, tako da mi moramo definirati samo drugu instancu koja će biti nosioc VLAN-ova 20 i 40.

S1(config)# spanning-tree mst configuration
S1(config-mst)# show current
Current MST configuration
Name      []
Revision  0     Instances configured 1

Instance  Vlans mapped
--------  ---------------------------------------------------------------------
0         1-4094
-------------------------------------------------------------------------------
S1(config-mst)# instance 1 vlan 20,40
S1(config-mst)# show pending
Pending MST configuration
Name      []
Revision  0     Instances configured 2

Instance  Vlans mapped
--------  ---------------------------------------------------------------------
0         1-19,21-39,41-4094
1         20,40
-------------------------------------------------------------------------------

Zatim ćemo dodijeliti ime regije i revizioni broj. Njih koristimo za indentificiranje switcheva koji pripadaju određenoj MST regiji.

S1(config-mst)# name Region1
S1(config-mst)# revision 1
S1(config-mst)# exit

Izlazak iz MST konfiguracionog režima će automatski aplicirati promjene; za izlazak iz MST konfiguracionog režima bez apliciranja promjena, koristimo abort.

Ova konfiguracija se mora aplicirati na sva tri switcha. Finalna MST konfiguracija izgleda ovako:

spanning-tree mst configuration
 name Region1
 revision 1
 instance 1 vlan 20, 40

Konfigurisaćemo S1 tako da postane root za instancu 0 (VLAN-ovi 10 i 30), a S2 će biti root za instancu 1 (VLAN-ovi 20 i 40):

S1(config)# spanning-tree mst 0 priority 0
S1(config)# spanning-tree mst 1 priority 4096

S2(config)# spanning-tree mst 0 priority 4096
S2(config)# spanning-tree mst 1 priority 0

Na kraju ćemo promijeniti spanning tree režim iz defaultnog PVST+ u MST na sva tri switcha:

S1(config)# spanning-tree mode mst

S2(config)# spanning-tree mode mst

S3(config)# spanning-tree mode mst

Sada možemo provjeriti i potvrditi da imamo dvije MST instance koje formiraju naše L2 topologije:

S3# show spanning-tree mst

##### MST0    vlans mapped:   1-19,21-39,41-4094
Bridge        address 000e.8316.f500  priority      32768 (32768 sysid 0)
Root          address 0013.c412.0f00  priority      0     (0 sysid 0)
              port    Fa0/13          path cost     0        
Regional Root address 0013.c412.0f00  priority      0     (0 sysid 0)
                                      internal cost 200000    rem hops 19
Operational   hello time 2 , forward delay 15, max age 20, txholdcount 6 
Configured    hello time 2 , forward delay 15, max age 20, max hops    20

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/13           Root FWD 200000    128.13   P2p 
Fa0/16           Altn BLK 200000    128.16   P2p

##### MST1    vlans mapped:   20,40
Bridge        address 000e.8316.f500  priority      32769 (32768 sysid 1)
Root          address 000f.345f.1680  priority      1     (0 sysid 1)
              port    Fa0/16          cost          200000    rem hops 19

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/13           Altn BLK 200000    128.13   P2p 
Fa0/16           Root FWD 200000    128.16   P2p

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who i'am?

komandant mark , January 23, 2011

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Ažurirano Nedjelja, 06 Juni 2010 17:45