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Spanning Tree Inter-connect with Catalyst

 

Introduction:

 

This document describes how to connect SG300 with Catalyst switch via STP.

 

Spanning Tree Protocol (STP) is a Layer 2 protocol that runs on mainly on switches. The specification for STP is IEEE 802.1D. The main purpose of STP is to ensure that you do not create loops when you have redundant paths in your layer 2 network.

 

STP stands for spanning tree protocol, RSTP stands for rapid STP, MSTP stands for multiple STP.

 

Catalyst switch default STP mode is PVST+, which runs STP for each VLAN, and encapsulates STP BPDU with VLAN tag (except VLAN 1).

 

For example, PVST+ BPDU for VLAN 2 is tagged with VLAN 2. While PVST+ BPDU for VLAN 1 is untagged.

 

Catalyst also supports rapid-PVST+ mode, which runs RSTP for each VLAN. STP BPDU is also encapsulated with VLAN tag.

 

PVST+ can setup different topology for different VLAN to achieve VLAN load balance.

 

SMB switch default STP mode is RSTP, and supports MSTP. SMB does not support PVST+ or rapid-PVST+.

 

Note: By default, Catalyst trunk allows all VLANs, while SMB switch allows no VLAN.

 

We need to remove extra VLANs from Catalyst and add required VLANs in SMB trunk to make VLANs match.

 

SMB switch can use default RSTP to connect to Catalyst switch in default PVST+ or rapid-PVST+ mode:

 

In this case, SMB switch and Catalyst switch are in different mode, there is boundary between them.

 

SMB STP communicates with Catalyst STP instance for VLAN 1. Catalyst STP BPDU for other VLANs pass through SMB switch as normal traffic.

 

PVST-RSTP.jpg

 

If Catalyst in PVST+ mode is root for VLAN 1, then PVST+ load balance cannot be achieved since SMB switch blocks all VLAN tagged PVST+ BPDU.

 

PVST-RSTP.2.jpg

 

But if we setup SMB switch as root, load balance can be achieved:

 

MSTP-PVST.LB.jpg

 

This is due to SMB switch ports are in forwading state and Catalyst tagged PVST+ BPDUs are passed through SMB STP region.

 

While in the diagram above, we need to use port priority to balance VLAN load, which is not a very trivial design.

 

So recommended connection mode is MSTP between SMB and Catalyst switch.

 

MSTP has multiple Spanning tree instances to build different topology for different vlan groups mapped to instance.

That  can be used for VLAN load balance, as illustrated below:

 

vlan 1-10 are mapped to MSTP instance 1

vlan 11-20 are mapped to MSTP instance 2

 

D1 is root for vlan 1-10, D2 is root for vlan 11-20.

SG300/500 as access switch dual-homed to two distribution layer catalyst switches.

SG300/500 load balance vlan 1-10 to uplink to D1 and vlan 11-20 to uplink to D2.

 

Note:

In order for MSTP to work properly, please configure the name, revision number, and vlan to instance mapping to be the sam

across connected MSTP switches. These switches are said to be in the same MSTP region.

Connectivity for switches in different MSTP regions is beyond the scope of this document.

 

For more information regarding Catalyst MSTP, please refer to

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_white_paper09186a0080094cfc.shtml

MSTP.jpg

 

Topology Diagram:

 

SG300 and 2 Catalyst form a triangle:

 

(f0/2) SW1.3560 (f0/4)-----(Gi1)SG300 (Gi8) --------(G0/2) SW2.3560 (g0/1)

 

MSTCSC.png

 

 

Configuration Overview:

 

 

SG300#sh cdp nei

 

Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge

 

                  S - Switch, H - Host, I - IGMP, r - Repeater, P - VoIP Phone

 

                  M - Remotely-Managed Device, C - CAST Phone Port,

 

                  W - Two-Port MAC Relay

 

    Device ID       Local      Adv  Time To Capability   Platform     Port ID

 

                    Interface  Ver. Live

 

------------------ ----------- ---- ------- ---------- ------------ -----------

 

       SW1             gi1      2     120     R S I    cisco        FastEtherne

 

                                                       WS-C3560-8PC t0/4

 

       SW2             gi8      2     138     R S I    cisco        GigabitEthe

 

                                                       WS-C3560C-8P rnet0/2

 

                                                       C-S

 

SG300(config)#do sh mac add

 

Aging time is 300 sec

 

  Vlan        Mac Address         Port       Type

 

-------- --------------------- ---------- ----------

 

   1       00:1a:e3:73:50:05      gi1      dynamic

 

   1       18:33:9d:03:a7:c0      gi1      dynamic

 

   1       64:d8:14:5d:14:13       0         self

 

SG300(config)#do sh arp

 

Total number of entries: 2

 

  VLAN    Interface     IP address        HW address          status

 

--------------------- --------------- ------------------- ---------------

 

vlan 1                1.1.1.1         00:1a:e3:73:50:40   dynamic

 

vlan 1     gi1        1.1.1.2         18:33:9d:03:a7:c0   dynamic

 

[

 

SW1 MAC: 00:1a:e3:73:50:40

 

SW2 MAC: 18:33:9d:03:a7:c0

 

SG300 MAC: 64:d8:14:5d:14:13

 

]

 

[SG300/3560 Spanning Tree Configuration]

 

 

 

SG300 does not support PVST (per vlan spanning tree) or rapid-PVST, uses MSTP to connect to Catalyst 3560 switch.

 

 

 

SG300 configration is the same as Catalyst switch.

 

spanning-tree mode mst

 

spanning-tree mst configuration

 

name TEST

 

 

Since SW1 has lowest MAC, it will be elected as ROOT.

SW2 has lower MAC than SG300, and is elected as designated for link with SG300.

SG300 Gi8 port will be blocked.

 

 

SG300#sh spanning-tree mst-configuration  [25 seconds]

 

Gathering information ..........

 

Current MST configuration

 

Name: TEST

 

Revision: 0

 

Instance  Vlans Mapped                                       State

 

--------  ------------------------------------------------   -----

 

0         1-4094                                             enabled

 

SG300#sh spanning-tree active [15 seconds]

 

Spanning tree enabled mode MSTP

 

Default port cost method:  long

 

Gathering information ..........

 

###### MST 0 Vlans Mapped: 1-20

 

CST Root ID    Priority    32768

 

               Address     00:1a:e3:73:50:00

 

               The IST ROOT is the CST ROOT

 

               Root Port   gi1

 

               Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec

 

IST Master ID  Priority    32768

 

               Address     00:1a:e3:73:50:00

 

               Path Cost   200000

 

               Rem hops    19

 

Bridge ID      Priority    32768

 

               Address     64:d8:14:5d:14:13

 

               Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec

 

               Max hops    20

 

  Name     State   Prio.Nbr    Cost    Sts   Role PortFast       Type

 

--------- -------- --------- -------- ------ ---- -------- -----------------

 

gi1       enabled  128.49    200000   Frw    Root No       P2P Intr

 

gi8       enabled  128.56    20000    Blk    Altn No       P2P Intr

 

----------------------------------------------------------------------------------------------------------------------------------------

 

 

 

SW1(config)#do sh span

 

MST0

 

  Spanning tree enabled protocol mstp

 

  Root ID    Priority    32768

 

             Address     001a.e373.5000

 

             This bridge is the root

 

             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

 

  Bridge ID  Priority    32768  (priority 32768 sys-id-ext 0)

 

             Address     001a.e373.5000

 

             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

 

Interface           Role Sts Cost      Prio.Nbr Type

 

------------------- ---- --- --------- -------- --------------------------------

 

Fa0/2               Desg FWD 200000    128.3    P2p

 

Fa0/4               Desg FWD 200000    128.5    P2p

 

SW2#sh span

 

MST0

 

  Spanning tree enabled protocol mstp

 

  Root ID    Priority    32768

 

             Address     001a.e373.5000

 

             Cost        0

 

             Port        1 (FastEthernet0/1)

 

             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

 

  Bridge ID  Priority    32768  (priority 32768 sys-id-ext 0)

 

             Address     1833.9d03.a780

 

             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

 

Interface           Role Sts Cost      Prio.Nbr Type

 

------------------- ---- --- --------- -------- --------------------------------

 

Fa0/1               Root FWD 200000    128.1    P2p

 

Gi0/2               Desg FWD 20000     128.10   P2p

 

Now let's change SG300's priority to 0 to make it ROOT

 

SG300(config)#spanning-tree priority 0

 

We can see now SG300 is root

 

SW1#sh span

 

MST0

 

  Spanning tree enabled protocol mstp

 

  Root ID    Priority    0

 

             Address     64d8.145d.1413

 

             Cost        0

 

             Port        5 (FastEthernet0/4)

 

             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

 

  Bridge ID  Priority    32768  (priority 32768 sys-id-ext 0)

 

             Address     001a.e373.5000

 

             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

 

Interface           Role Sts Cost      Prio.Nbr Type

 

------------------- ---- --- --------- -------- --------------------------------

 

Fa0/2               Altn BLK 200000    128.3    P2p

 

Fa0/4               Root FWD 200000    128.5    P2p

 

And SW2 elected as designated switch due to its link cost to ROOT switch is better [1000M] than SW1 [100M]

 

We can modify interface level spanning tree parameters:

 

SG300(config)#int gi 1

 

SG300(config-if)#spanning-tree

 

  bpdu                 Configure BPDU handling when STP is disabled.

 

  bpduguard            Protect network from unexpected BPDU packets

 

  cost                 Change an interface's spanning tree path cost

 

  disable              Disable spanning-tree on an interface

 

  guard                Guard the interface

 

  link-type            Override the default link-type setting

 

  mst                  Configure the MSTP Subsystem

 

  port-priority        Change an interface's spanning tree priority (in steps

 

                       of 16)

 

  portfast             Allow to move directly to the forwarding state when

 

                       linkup occurs

 

[bpdu filter]

 

SG300(config-if)#spanning-tree bpdu

 

  filtering            Specify that when spanning tree is disabled on the

 

                       interface, BPDU packets would be filtered.

 

  flooding             Specify that when spanning tree is disabled on the

 

                       interface, untagged BPDU packets would be flooded

 

                       unconditionally (Without applying VLAN rules), to all

 

                       ports with spanning tree disabled. Tagged BPDU packets

 

                       would be filtered.

 

[root guard]

 

SG300(config-if)#spanning-tree guard

 

  root                 Guard the interface from becoming root port

 

SG300(config-if)#spanning-tree mst 1

 

  cost                 Change an interface Spanning Tree path cost for a

 

                       specific instance.

 

  port-priority        Change an interface Spanning Tree priority (in steps

 

                       of 16) to a specific instance.

 

SG300(config-if)#spanning-tree link-type

 

  point-to-point       Specify that the link type of a port is point-to-point

 

  shared               Specify that the link type of a port is shared

 

And we can also tune spanning tree parameters:

 

SG300(config)#spanning-tree

 

  bpdu                 Configure BPDU handling when STP is disabled.

 

  forward-time         Set a Spanning Tree FORWARD Interval

 

  hello-time           Set a Spanning Tree HELLO Interval

 

  max-age              Set a Spanning Tree MAX AGE Interval

 

  mode                 Spanning tree protocol type

 

  mst                  Configure MSTP Subsystem

 

  pathcost             Spanning tree path-cost method

 

  priority             Specify a Spanning Tree Priority (in steps of 4096)

 

   <CR>

 

SG300(config)#spanning-tree hello-time

 

  <1-10>               Set a Spanning Tree HELLO Interval

 

SG300(config)#spanning-tree hello-time 1

 


SG300#sh cdp nei

 

Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge

 

                  S - Switch, H - Host, I - IGMP, r - Repeater, P - VoIP Phone

 

                  M - Remotely-Managed Device, C - CAST Phone Port,

 

                  W - Two-Port MAC Relay

 

    Device ID       Local      Adv  Time To Capability   Platform     Port ID

 

                    Interface  Ver. Live

 

------------------ ----------- ---- ------- ---------- ------------ -----------

 

       SW1             gi1      2     120     R S I    cisco        FastEtherne

 

                                                       WS-C3560-8PC t0/4

 

       SW2             gi8      2     138     R S I    cisco        GigabitEthe

 

                                                       WS-C3560C-8P rnet0/2

 

                                                       C-S

 

SG300(config)#do sh mac add

 

Aging time is 300 sec

 

  Vlan        Mac Address         Port       Type

 

-------- --------------------- ---------- ----------

 

   1       00:1a:e3:73:50:05      gi1      dynamic

 

   1       18:33:9d:03:a7:c0      gi1      dynamic

 

   1       64:d8:14:5d:14:13       0         self

 

SG300(config)#do sh arp

 

Total number of entries: 2

 

  VLAN    Interface     IP address        HW address          status

 

--------------------- --------------- ------------------- ---------------

 

vlan 1                1.1.1.1         00:1a:e3:73:50:40   dynamic

 

vlan 1     gi1        1.1.1.2         18:33:9d:03:a7:c0   dynamic

 

[

 

SW1 MAC: 00:1a:e3:73:50:40

 

SW2 MAC: 18:33:9d:03:a7:c0

 

SG300 MAC: 64:d8:14:5d:14:13

 

]

 

[SG300/3560 Spanning Tree Configuration]

 

SG300 does not support PVST (per vlan spanning tree) or rapid-PVST, uses MSTP to connect to Catalyst 3560 switch.

 

SG300 configration is the same as Catalyst switch.

 

spanning-tree mode mst

 

spanning-tree mst configuration

 

name TEST

 

Since SW1 has lowest MAC, it will be elected as ROOT.

 

SW2 has lower MAC than SG300, and is elected as designated for link with SG300.

 

SG300 Gi8 port will be blocked.

 

SG300#sh spanning-tree mst-configuration  [25 seconds]

 

Gathering information ..........

 

Current MST configuration

 

Name: TEST

 

Revision: 0

 

Instance  Vlans Mapped                                       State

 

--------  ------------------------------------------------   -----

 

0         1-4094                                             enabled

 

SG300#sh spanning-tree active [15 seconds]

 

Spanning tree enabled mode MSTP

 

Default port cost method:  long

 

Gathering information ..........

 

###### MST 0 Vlans Mapped: 1-20

 

CST Root ID    Priority    32768

 

               Address     00:1a:e3:73:50:00

 

               The IST ROOT is the CST ROOT

 

               Root Port   gi1

 

               Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec

 

IST Master ID  Priority    32768

 

               Address     00:1a:e3:73:50:00

 

               Path Cost   200000

 

               Rem hops    19

 

Bridge ID      Priority    32768

 

               Address     64:d8:14:5d:14:13

 

               Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec

 

               Max hops    20

 

  Name     State   Prio.Nbr    Cost    Sts   Role PortFast       Type

 

--------- -------- --------- -------- ------ ---- -------- -----------------

 

gi1       enabled  128.49    200000   Frw    Root No       P2P Intr

 

gi8       enabled  128.56    20000    Blk    Altn No       P2P Intr

 

----------------------------------------------------------------------------------------------------------------------------------------

 

SW1(config)#do sh span

 

MST0

 

  Spanning tree enabled protocol mstp

 

  Root ID    Priority    32768

 

             Address     001a.e373.5000

 

             This bridge is the root

 

             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

 

  Bridge ID  Priority    32768  (priority 32768 sys-id-ext 0)

 

             Address     001a.e373.5000

 

             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

 

Interface           Role Sts Cost      Prio.Nbr Type

 

------------------- ---- --- --------- -------- --------------------------------

 

Fa0/2               Desg FWD 200000    128.3    P2p

 

Fa0/4               Desg FWD 200000    128.5    P2p

 

SW2#sh span

 

MST0

 

  Spanning tree enabled protocol mstp

 

  Root ID    Priority    32768

 

             Address     001a.e373.5000

 

             Cost        0

 

             Port        1 (FastEthernet0/1)

 

             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

 

  Bridge ID  Priority    32768  (priority 32768 sys-id-ext 0)

 

             Address     1833.9d03.a780

 

             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

 

Interface           Role Sts Cost      Prio.Nbr Type

 

------------------- ---- --- --------- -------- --------------------------------

 

Fa0/1               Root FWD 200000    128.1    P2p

 

Gi0/2               Desg FWD 20000     128.10   P2p

 

Now let's change SG300's priority to 0 to make it ROOT

 

SG300(config)#spanning-tree priority 0

 

We can see now SG300 is root

 

SW1#sh span

 

MST0

 

  Spanning tree enabled protocol mstp

 

  Root ID    Priority    0

 

             Address     64d8.145d.1413

 

             Cost        0

 

             Port        5 (FastEthernet0/4)

 

             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

 

  Bridge ID  Priority    32768  (priority 32768 sys-id-ext 0)

 

             Address     001a.e373.5000

 

             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

 

Interface           Role Sts Cost      Prio.Nbr Type

 

------------------- ---- --- --------- -------- --------------------------------

 

Fa0/2               Altn BLK 200000    128.3    P2p

 

Fa0/4               Root FWD 200000    128.5    P2p

 

And SW2 elected as designated switch due to its link cost to ROOT switch is better [1000M] than SW1 [100M]

 

We can modify interface level spanning tree parameters:

 

SG300(config)#int gi 1

 

SG300(config-if)#spanning-tree

 

  bpdu                 Configure BPDU handling when STP is disabled.

 

  bpduguard            Protect network from unexpected BPDU packets

 

  cost                 Change an interface's spanning tree path cost

 

  disable              Disable spanning-tree on an interface

 

  guard                Guard the interface

 

  link-type            Override the default link-type setting

 

  mst                  Configure the MSTP Subsystem

 

  port-priority        Change an interface's spanning tree priority (in steps

 

                       of 16)

 

  portfast             Allow to move directly to the forwarding state when

 

                       linkup occurs

 

[bpdu filter]

 

SG300(config-if)#spanning-tree bpdu

 

  filtering            Specify that when spanning tree is disabled on the

 

                       interface, BPDU packets would be filtered.

 

  flooding             Specify that when spanning tree is disabled on the

 

                       interface, untagged BPDU packets would be flooded

 

                       unconditionally (Without applying VLAN rules), to all

 

                       ports with spanning tree disabled. Tagged BPDU packets

 

                       would be filtered.

 

[root guard]

 

SG300(config-if)#spanning-tree guard

 

  root                 Guard the interface from becoming root port

 

SG300(config-if)#spanning-tree mst 1

 

  cost                 Change an interface Spanning Tree path cost for a

 

                       specific instance.

 

  port-priority        Change an interface Spanning Tree priority (in steps

 

                       of 16) to a specific instance.

 

SG300(config-if)#spanning-tree link-type

 

  point-to-point       Specify that the link type of a port is point-to-point

 

  shared               Specify that the link type of a port is shared

 

And we can also tune spanning tree parameters:

 

SG300(config)#spanning-tree

 

  bpdu                 Configure BPDU handling when STP is disabled.

 

  forward-time         Set a Spanning Tree FORWARD Interval

 

  hello-time           Set a Spanning Tree HELLO Interval

 

  max-age              Set a Spanning Tree MAX AGE Interval

 

  mode                 Spanning tree protocol type

 

  mst                  Configure MSTP Subsystem

 

  pathcost             Spanning tree path-cost method

 

  priority             Specify a Spanning Tree Priority (in steps of 4096)

 

   <CR>

 

SG300(config)#spanning-tree hello-time

 

  <1-10>               Set a Spanning Tree HELLO Interval

 

SG300(config)#spanning-tree hello-time 1

Related Information:

Small Business 300 Series Managed Switch Administration Guide Release 1.3

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