802.1d spanning tree 7 hops limitation

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Apr 18th, 2007
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Hi all,

I would clarify for the 802.1d spanning tree standard. It states that it is 7 hops count limitation.

Is it mean that only <=7 hops in a particular loop?

What's happening if it is more that 7 hops, i.e. switches?


Thanks a lot in advance


mak

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Amit Singh Wed, 04/18/2007 - 22:05
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Hi Mak,


With IEEE 802.1d,recommended consideration when designing the network with STP is not more than 7 hops. On the default timer parameters STP is expected to work fine till 7 hops. Beyond 7 hops the STP will work but it might bit a little hard to predict the behaviour of the STP, which might result in a lots of network problems. From an individual switch perspective like from the root bridge the STP diameter should not be more than 7 hops away.


HTH,

-amit singh

ariela Wed, 04/18/2007 - 22:15
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Hi mak,


first of all, is a physical limitation.

Please take a look here:

http://www.ieee802.org/1/files/public/docs2006/avb-azarov-distortion-quantify-060816.pdf


another good point of view:

http://home.caregroup.org/templatesnew/homepage/homepage_out.asp?pageid=4671


The limit of 7 hops in the standard was the result of extensive simulations done at DEC in the late 80s, using some fairly delay-sensitive protocols as a benchmark (e.g. LAT). That is the 802.1D standard recommends a maximum bridged LAN diameter of 7 hops, as stated. The issue is more with non-routed protocols (e.g., LAT, LAVc, NetBIOS, etc.) that are somewhat delay sensitive. Having a large number of bridge hops could cause application problems.


HTH

Andrea

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