PVST+和RSTP混合使用

ssffzz1

關(guān)掉的話，你就單純的靠人工來保證無環(huán)吧。

ssffzz1

對(duì)一些特殊的MAC是要檢查的。是一個(gè)特殊的MAC前綴01:

要按照你的理論的話，STP BPDU就實(shí)現(xiàn)不了了。

ssffzz1

好像是，第7個(gè)bit 為1。我沒找到可靠的資料。

ssffzz1

呵呵。沒什么。技術(shù)這個(gè)東西就是很微妙的。

所以說沒事別搞網(wǎng)絡(luò)。害人啊。

gdxnfx

原帖由 ssffzz1 于 2009-8-24 20:47 發(fā)表
PVST+的PID字段，0X010B
此字段是SNAP封裝的TYPE字段，以太網(wǎng)要求小于0X600,用于區(qū)分TYPE和LENGTH,此值小于0x600會(huì)導(dǎo)致不支持PVST+的設(shè)備識(shí)別錯(cuò)誤而丟棄報(bào)文，因此PVST+的BPDU無法透?jìng)�，PVST+無法正常工作。
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802.1d bpdu :
An IEEE 802.1d Bpdu has the following format:

protocol id:   0000 IEEE 802.1d
version id:    00
bpdu type:     00 config bpdu, 80 tcn bpdu
bit field:     1 byte
  1 : topology change flag
  2 : unused    0
  3 : unused    0
  4 : unused    0
  5 : unused    0
  6 : unused    0
  7 : unused    0
  8 : topology change ack
root priority    2 bytes
root id:         6 bytes
root path cost:  4 bytes
bridge priority: 2 bytes
bridge id:       6 bytes
port id:         2 bytes
message age:     2 bytes in 1/256 secs
max age:         2 bytes in 1/256 secs
hello time:      2 bytes in 1/256 secs
forward delay:   2 bytes in 1/256 secs



Few changes have been introduced by RSTP to the BPDU format. Only two flags, Topology Change (TC) and TC Acknowledgment (TCA), are defined in 802.1D. However, RSTP now uses all six bits of the flag byte that remain in order to perform:

Encode the role and state of the port that originates the BPDU

Handle the proposal/agreement mechanism

Another important change is that the RSTP BPDU is now of type 2, version 2. The implication is that legacy bridges must drop this new BPDU. This property makes it easy for a 802.1w bridge to detect legacy bridges connected to it.