Traffic forwarding through interswitch links

Consider a PVLAN network topology where secondary VLANs have been configured on a set of access switches but only one of these switches has uplink connectivity. The secondary VLAN traffic on switches that do not have an uplink configured must be forwarded through interswitch links to the device that has an uplink.

As secondary VLAN traffic traverses the interswitch links, all switches in the path use the secondary VLAN information carried in the frame to ensure that PVLAN traffic forwarding rules are preserved.

For example, for an isolated VLAN, each switch must ensure the following:

  • Traffic from the isolated VLAN is forwarded to a switch that has a promiscuous port.

  • Traffic from an isolated VLAN is not forwarded to any local community ports or to other isolated VLANs.

Figure 23: Interswitch link traffic forwarding