Apply concepts of RSTP

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NAME: ADNAN ROLL NO: 21MECSN O3 
 
 
Assignment #2 ME-CSN, Advanced Computer Networks 
 
(a) Apply concepts of RSTP, determine the root bridge, and label 
DP, BP and RP. 
(b) For the segment Net W, label DP and AP. Port ID C1<C2<C3<C4. 
❖ RSTP determines the root bridge based on bride ID, A bridge have 
a lower priority to increase the chances that it is selected as 
the root bridge if priority is same than we preferred to select 
the lowest mac address as root bridge. 
 
NAME: ADNAN ROLL NO: 21MECSN O3 
(b) Write the state/role of each port. 
• Root Bridge 
➢ serves as a reference point for all spanning-tree 
calculations to determine which redundant paths to block. 
• Root Port 
➢ It is the port on the Bridge (Switch) with the least 
Spanning Tree Path Cost from the switch to the root 
bridge. 
• The port that receives the best BPDU on a bridge is the 
root port. This is the port that is the closest to the root 
bridge in terms of path cost. 
• Designated ports 
➢ are selected on a per-segment basis, based on the cost of 
each port on either side of the segment and the total 
cost calculated by STP for that port to get back to 
the root bridge. 
• Alternate and Backup Port Roles 
➢ These two port roles correspond to the blocking state of 
802.1D. A blocked port is defined as not being the 
designated or root port. A blocked port receives a more 
useful BPDU than the one it sends out on its segment. 
Remember that a port absolutely needs to receive BPDUs to 
stay blocked. RSTP introduces these two roles for this 
purpose. 
➢ An alternate port receives more useful BPDUs from another 
bridge and is a port blocked 
(c) Assume port C3 goes down, which states (roles) the ports would 
be? How much approximate time would be taken for convergence? 
➢ The C3 port goes down the C4 port comes to forwarding 
state /Designated forwarding state in below figure (2) it 
shows before and after states of port C4. 
figure (2) 
Designated 
Forward