DTP with an hub.

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Aug 9th, 2010
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About DTP, someone knows what happens if I link three interfaces of three different switches with an hub.

Cisco says that DTP should be used as a point to point protocol, but in that case is it possible that two of

the three switches negotiate a trunk while the third remains out? Thanks.

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Giuseppe Larosa Mon, 08/09/2010 - 08:12
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Hello Matteo,

in real world nowdays it is becoming difficult to find an hub ....

ISL should allow for multipoint connection at least in theory.

802.1Q should be point to point in nature.

if all devices are capable of using ISL they could attempt to setup an ISL trunk.

However, the half duplex limitation that comes from using a true hub makes this kind of connections real bottlenecks to be avoided in modern networks

Hope to help


speculor_cisco Mon, 08/09/2010 - 08:46
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Hello Giuseppe and thanks for your answer.

When you say "802.1Q should be point to point in nature" I could imagine that Cisco,

in a scenario with a hub, let a switch interface to maintain only one DTP session identified

by the MAC of the other interface, that among the others with wich the session is established.

But in the case of 4 switches, anyway would be possible to have 2 different sessions between two

different couples of switches. Why does not Cisco give official detailed informations about the protocol?

Is it possible that, if someone was really interested to know the work of this scenario, the only way

is a lab and inverse engineering?


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