Switch 1 Switch 2 Switch 3 Blocking Forwarding ROOT BRIDGE BRIDGE’S ROOT PORT DESIGNATED PORT DESIGNATED BRIDGE

ISL Header 26 Bytes Encapsulated Ethernet Frame ISL FCS 4 Bytes DA TypeUserSALENAAAA03HSAVLANBPDUINDEXRES ISL Header Dest Priority 802.1Q Header SrcTagLen/E typeDataFCS New Calculation VLAN-ID Original Ethernet Frame 4 Byte Tag Added

Switch 1 VLAN1 VLAN2 Switch 2 VLAN1 VLAN2 Trunk VLAN IDEthernet Frame

Switch 1 Switch 2 Switch 3 Discarding Forwarding ROOT BRIDGE BRIDGE’S ROOT PORT DESIGNATED PORT DESIGNATED RSTP ALTERNATE PORT Forwarding Discarding RSTP BACKUP PORT HUB

Dst: Dst: Src: Dst: Inside Local NAT Src: Dst: Src: Src: Inside GlobalOutside Global Outside Local IP address assigned to the host in the private network IP address representing the outside host in the private network IP address representing the inside host on the external network IP address assigned to the host on the external network Local Global “Host A” pings “Router B” A B