Packet Tracer: Cisco, Spanning tree protocol
- 1. Rafat Khandaker Packet Tracer Spanning Tree Protocol/PVST / RSTP 05/05/16 ABSTRACT In this Lab simulation, four switches have been set up to separate multiple hosts on a network. The purpose of this simulation is to understand the concept of the spanning tree protocol. The hosts on the network have been separated into different vlans in order to enable PVST configuration. INTRODUCTION: The Spanning tree protocol was designed in order to prevent redundant paths within a network. When 3 or more switches are connected together with more than one possible path to designated target host; it is possible to create an endless loop, creating a broadcast storm. This problem is due to the switches' lacking ability to separate broadcast domains; for example, when a packet with an unknown destination mac address enters a switch, the switch will send a broadcast arp request until it learns the destination to the host. At this time, the switch to switch recieving the broadcast of FF:FF:FF:FF:FF:FF will be forwarded out of all ports and the cycle will continue through other switches, creating denial of service or bandwith overload. To fix this problem, often times a network in the below example will have separate VLANS along with RSTP + PVST configured. The RSTP (802.1W) protocol is an enhancement of the original STP 802.1D protocol. Rapid spanning tree combines the operations of Learning, Blocking and disabled port state into one operation, called discarding state, It has a much faster convergance time. When configured with Rapid PVST, RSTP can converge for each virtual lan interface. According to cisco, the default spanning tree protocol is set to Rapid PVST+. STP also use BPDU ( Bridged Protocol Data Units ) , which are stp frames, to construct a loop free path. BPDUs are 16 bit added information, attached to the frame of the packet. Spanning tree topology is calculated by using the root bridge as the primary sender for all BPDUs. The Root bridge will have all it's interfaces as designated ports. The other switches should have atleast one root bridge port, which is the shortest path to the bridge. One interace on the all the switches should be in the discarding state.
- 2. CONFIGURING IP FOR ALL HOSTS
- 3. SWITCH 0
- 5. SWITCH 1 **notice here taht the spanning tree is configured for vlan 2, If i were to scroll down, the spanning tree is different for each vlan. **
- 6. SWITCH 2
- 7. * WE CAN SEE HERE THAT SWITCH 2 ASSUMED THE ROOT SWITCH POSITION* SWITCH 3
- 8. FINAL TOPOLOGY EXAMPLES FROM OTHER SOURCES.
- 9. RESOURCE : http://www.cisco.com/c/en/us/support/docs/switches/catalyst-6500-series- switches/72836-rapidpvst-mig-config.html According to the cisco documentation, R-PVST configuration are used with two or more core distribution switches. The distribution switches are manually assigned to carry vlan trunk information on vlan groups. This is most likely done to reduce bandwidtch congestion and security. I realized that even though this network is configured with R-PVST , it is configured with RSTP for each vlan. We can actually see from the Show span configuration that the spanning tree is autoconfigured with a priority for each Vlan, separately. The configuration I found in the cisco documentation clearly shows the difference, in an actual R-PVST network. In here trunk links between the distribution switches are manually assigned between 2 disribution devices. In this configuration, Distribution 1 will be the root bridge, manually assigned for vlan 10,30,100. Distribution will be the root bridge, manually assigned for vlan 20,40,200. the configuration:
- 10. We can see that the individual trunk links for each switch are manually set to carry certain vlan information. Another Source from Youtube
- 11. https://www.youtube.com/watch?v=6AxDqaG9M7I From this example, I realized that my previous configuration can be set to PVST or R-PVST simply by manually configuring the root bridge for each vlan. I can also manually configure the trunk links to only send vlan traffic in certain links.
- 12. CONCLUSION I have successfully configured STP and RSTP, P-VST on cisco switches. The concepts and actual implementation of PVST had to be analyzed in depth. From this simulation, I was able to reassess and correct my knowledge of the STP Protocol.