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White Paper Issue: October 2006 Integration of BX600 SB9 Switches in Cisco Networks Page 15 / 47
2.4.2 Recommended Solution
As discussed earlier, there are a number of different combinations of STP protocols that can be selected when integrating SB9
switches into Cisco networks. Although using MSTP between the Cisco and the SB9 would be the best solution, it will not be
discussed further in this paper because MSTP is so very unusual in Cisco networks. If you were to run MSTP (802.1s) on the
SB9 switches while using STP or RSTP at the Cisco switches, MSTP would fall back to RSTP and STP respectively.
The resulting and possible solutions are shown in Table 4.
SB9 Switch
802.1D 802.1w No STP
PVST+ Ok* Ok Ok
Cisco
Switch
RAPID-
PVST
with restrictions
(Problems with TCN)
with restrictions
(Problems with TCN)
Ok
Table 4 : Possible STP combinations when using VLAN Trunks
* SB9 firmware >1.14 required
The recommended solution when running STP over VLAN trunks between Cisco and SB9 switches is to disable STP completely
at the SB9 and run the STP or RSTP protocol at the Cisco switches (see Figure 4 and Figure 7).
When the SB9 is connected to Cisco switches without VLAN trunks, the preferred solution is RSTP, because this would lead to
the shortest failover times.
Caution: In order to avoid loops in the network, please be sure that the VLAN configuration on both uplinks is
the same. Misconfiguration may lead to unidirectional links and to network loops!
Caution: There is a significant difference between disabling STP on the SB9 globally and for each interface:
If STP is disabled for one interface BPDUs are neither sent nor bridged. This behavior may lead to
network loops.
When STP is disabled globally BPDUs are bridged. This is needed in the recommended scenarios.
Caution: When running STP on an SB9 it is important to enable STP at all ports, especially when creating port-
channels: this is not the default and must be enabled manually.
2.4.3 Configuration with VLAN Trunks
You set up the scenario shown in Figure 8 by performing the following steps:
• Step 1: Configure the switches
• Step 2: Verify the configuration
SB9
STP disabled
Cisco A
priority 0 for all vlans
Po1
Po1
Po2
Po2
Po3 Po3
On all trunks:
VLAN 1 native
VLAN 10 tagged
VLAN 20 tagged
Cisco B
priority 4096 for all vlans
Alternate
discarding
Root port
forwarding
Designated port
forwarding
Designated port
forwarding
Gi 0/1
Gi 0/1 Gi 0/2
Gi 0/1
0/11
0/12
0/13
0/14
Gi 0/23
Gi 0/24
Gi 0/23
Gi 0/24
Figure 8 : Configuration example RAPID-PVST while STP is disabled at SB9
Step 1: Configure the switches
! SB9 configuration
!
! Disable STP for the whole switch
! (This command is normally not displayed)
no spanning-tree