RSTP 的收敛过程
RSTP (IEEE 802.1w)
RSTP与标准STP(IEEE 802.1D)的最主要区别是RSTP不再依赖转发延迟的计时器( Forward Delay timer)。RSTP通过Proposal/Agreement机制缩短收敛时间。
的规则,如果连续个丢失(默认根据RSTP三个BPDU6秒),则认为交换机之间的RSTP关系中断。较短的失效时间便于更快的探测故障。
标准STP有五个端口状态(Port State),RSTP缩减为三个端口状态。
RSTP BPDU
Proposal 和Designated port
P l D i t d t
Agreement 和Root port
RSTP 端口状态
STP/RSTP收敛过程的三个步骤
步骤1 选根桥
步骤2 选根端口
步骤3 选指定端口
1. BPDU RID=BID of A p4p3p5
BID=32,768.0000.0C55.5555
BID=32,768.0000.0C33.3333p10Proposal
p10 port role: designated port no forwarding no learning Path Cost=19Sender BID =BID of D New link p6C
Cost = 19BPDU RID=BID of A
Path Cost=19
Sender BID = BID of B Cost = 19
Sender BID = BID of D 1. BPDU RID=BID of A Proposal
p9 port role: designated port no forwarding
BID=32,768.0000.0C22.2222
p9: designated port p10: designated port p9
no forwarding
p6
C Cost = 19Cost = 19
2.BPDU Sender BID B
Path Cost=19+19=38
New link DP BID=32,768.0000.0C22.2222
Path Cost=19 + 19 = 382.BPDU Sender BID D
Path Cost=19+ 19 = 38P9P th C t 6的相同
p9
的Path Cost 值与p6的相同。D 交换机的Sender BID 比B 的小。