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RSTP Hello Time IEEE-2004

chaitanya780
Level 1
Level 1

Hello Experts,

i would like to know how bridges that are connected to non-root bridges will learn the hello time(non default value) configured at the root Bridge.  in the below topology NonRootBr1 should relay the hellotime to NonRootBr2. but as per the standard i didnt understand how NonRootBr2 learns root HelloTime.

||RootBridge(helloTime-10)||----------||NonRootBr1(default)||----------||NonRootBri2(default)||

Standard Says rstp code should use the designatedTimes in BPDU, also standard says that update designatedTimes.helloTime with the BridgeTimes.hellotime. so if NonRootBr1 sends its local hellotime , how NonRootBr2 learn hello time at Root Bridge. 

From Standard(8021D 2004): 

17.21.20 txRstp()

The value of the Message Age, Max Age, Fwd Delay, and Hello Time parameters
conveyed in the BPDU are set to the values held in designatedTimes (17.19.5) for the Port.

17.21.25 updtRolesTree()

The designatedTimes (17.19.5) for each Port, set equal to the value of rootTimes, except for the
Hello Time component, which is set equal to BridgeTimes’ Hello Time

Thanks & Regards 

chaitanya

1 Reply 1

acampbell
VIP Alumni
VIP Alumni

Hi,

 

Have a read at this document.

https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/24062-146.html

Search within for "hello" , a good explanation is given.

Regards, Alex. Please rate useful posts.
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