Number of Spanning Tree instances per VLAN?

TestOut says...
802.1q only supports one instance per VLAN
ISL supports multiple

Odom says in the Intro book...
Both 802.1q and ISL allows a spanning tree instance

Actually, the question in the Intro is pretty vague...

Which of the following allows a spanning tree instance per VLAN?
a. VTP
b. ISL
c. 802.1q
d. Both ISL and 802.1q
e. None of the above

I choose C, because I figured a to mean one instance...

The book goes on to say that one of the stated differences between the two trunking protocols was that 802.1q did not support multiple spanning trees...

I know both of them supports at least 1 instance, so I'm assuming that it's a trick question and that ISL supports multiple and 802.1q only supports 1...

Find more posts tagged with

Free for TechExams community: Cybersecurity salary guide

Compare cert salaries and plan your next career move

Button

Comments

Netstudent

Both can support a spanning tree insatnce for each VLAN. ISL uses PVST and dot1q uses PVST+

There are a couple good STP threads going in the CCNP forum that will probably answer your question.

dtlokee

The 802.1q standard supports 1 instance of STP for all VLANs, but who is Cisco to follow a standard? Cisco uses PVST+ for 802.1q trunks allowing a singles instance fore each VLAN.