On a live network, a VBST-enabled device may connect to a device enabled with PVST/PVST+/Rapid PVST+. Interworking Between VBST and PVST/PVST+/Rapid PVST+ When a VBST-enabled device connects to an STP/RSTP-enabled device, the trunk interface must be used to connect the two devices and the blocking point must be located on the VBST-enabled device to implement load balancing. Because STP/RSTP does not differentiate VLANs, a spanning tree shared by VLANs is formed. Topology calculation is performed as defined by STP/RSTP.
On an access interface, a VBST-enabled device uses standard STP or RSTP BPDUs to exchange with the remote end according to the VLAN that the access interface belongs to. VBST BPDUs from VLAN10 can be forwarded along the spanning tree in VLAN1, that is, VLAN10 and VLAN1 share the spanning tree, as shown in Figure 11-3. SwitchB cannot forward VBST BPDUs from VLAN10 and no loop occurs in VLAN10, so spanning tree calculation in VLAN10 is not triggered. STP/RSTP runs on SwitchB, so the blocking port exists on SwitchB. Then the spanning trees in VLAN1 and VLAN10 are formed, as shown in Figure 11-3.Īssume that the blocking point of the spanning tree in VLAN1 is on SwitchB. SwitchA and SwitchB transparently transmit VBST BPDUs in VLAN10, so only four interfaces on SwitchC and SwitchD participate in spanning tree calculation in VLAN10. Loops occur in VLAN10, so spanning tree calculation in VLAN10 is triggered. SwitchD can still receive and forward VBST BPDUs in VLAN10. Runs on SwitchD, so the congestion point exists in VLAN1. Devices are connected through trunk interfaces, and interfaces on SwitchA through SwitchD allow packets from VLAN1 and VLAN10 to pass through.įigure 11-3 Interworking between VBST and STP/RSTP on a trunk interfaceĪn STP/RSTP-enabled device can only send and receive STP/RSTP BPDUs, and transparently transmit VBST BPDUs, so a spanning tree is formed in VLAN1 as defined by STP/RSTP.Īssume that the congestion point of the spanning tree in VLAN1 is on SwitchD. The following describes spanning tree implementation, as shown in Figure 11-3.Īs shown in Figure 11-3, STP/RSTP is deployed on SwitchA and SwitchB, and VBST is deployed on SwitchC and SwitchD. When a VBST-enabled device connects to an STP-enabled device, the VBST-enabled device uses standard STP BPDUs in VLAN1 and VBST BPDUs with the Data field of STP BPDUs in other VLANs to exchange with the STP-enabled device.When a VBST-enabled device connects to an RSTP-enabled device, the VBST-enabled device uses standard RSTP BPDUs in VLAN1 and VBST BPDUs with the Data field of RSTP BPDUs in other VLANs to exchange with the RSTP-enabled device.To implement interworking between VBST and standard STP/RSTP, take the following measures: VBST and STP/RSTP use different BPDU formats, so there are interworking problems. On a live network, VBST-enabled devices may connect to STP/RSTP-enabled devices. Interworking Between VBST and Standard STP/RSTP
0 kommentar(er)
