VLaN question

say there are for switches connected in a loop and 3 vlans.

how do you know where a certain switch has learned its vlan info.

is it sh vtp status...... if so what i am looking for apart from the mode.if it was in server mode, this doesnt mean it hasnt learnt it if from its neighbor does it ----so how do i know here it has learned its vlan info..

remember you can only console into to one switch and not telnet others

cheers guys

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Comments

mikej412

Well with four routers, figure they are in a physical diamond formation -- and STP takes care of the loop -- so there may be a physical connection, but there is no loop. So you actually wind up with 4 routers in a logical line.

The change has to be made on a server for the change to propagate to the other switches (and one server or 4 servers doesn't make a difference as long as the switches are setup correctly in the same VTP domain or in transparent mode).

The VTP updates will come from the updated VTP server through any other domain switches (or transparent mode switches) in the loop free link.

If one switch is between 2 VTP servers -- look at the "Configuration last modified...." part of the sh vtp status command -- hopefully that points you in the correct direction (left switch or right switch). Without checking on real equipment -- your mileage may vary.

ceejay3001

thanks for that ---my only query is if there are 4 switches one router. and you can only console into one switch. do a sh vtp status --and this shows up as client mode - then how would you know where the switch learned its vlan info --for example it is directly connected to 2 switches

mikej412

ceejay3001 wrote:

do a sh vtp status --and this shows up as client mode - then how would you know where the switch learned its vlan info --for example it is directly connected to 2 switches

The last couple of lines of the sh vtp status has that "Configuration last modified...." that I mentioned above. That should contain the IP address of the device that last modified the configuration.

If you have access to at least 2 switches, you should be able to confirm this.

ceejay3001

thanks for your reply,

i see what you mean about the last conf ip address.

we are assuming there 4 switches like below --and 3 vlans - notice sw2 is not connected to sw4. and sw1 not going to sw3.

......sw2
sw1< >sw3
......sw4

i have this set up on netsim --i have sw3 set as vtp server the rest are transparent. if i add a vlan on sw3 it does show up on all the others.

when i do sh vtp status
the config last modified by and local update ip state is 0.0.0.0. and i do have ip addresses set up the switches.

so how do i prove where sw1,2,4 got there vlan info.

so is there two ways of finding out where the sw2 for example learnd its vlan config.

1) look at the config register--people have said this -but i dont get how this proves wheres the switch learned it vlan info. just states it was updated!!am i right

2) config last modified. just like you said.

im sure this will show up in the exam and really need to know the best and quicked straight forwared to find out the only switch i can console into learned its vlan info --

also if it was learned locally how would i know this--simply by the switch being in server mode!!

thankyou

mikej412

ceejay3001 wrote:

also if it was learned locally how would i know this--simply by the switch being in server mode!!

probably the the IP address matching the switch admin address (in case there were multiple VTP server out there).

There is also the local id -- but I can't remember what its significance was.

Different simulaters either don't work well, or show different things here -- so its something to test on real hardware (but I doubt/hope that Cisco wouldn't test on something this obscure).

Thats the fun of using simulators -- you either waste time because of the limitations of the simulator..... or you learn other stuff by mistake.

Anyone have have 4 good switches handy? Some time? And the urge to post the real switch output?

mikej412

ceejay3001 wrote:

i have this set up on netsim --i have sw3 set as vtp server the rest are transparent. if i add a vlan on sw3 it does show up on all the others.

when i do sh vtp status
the config last modified by and local update ip state is 0.0.0.0. and i do have ip addresses set up the switches.

The transparent switches should pass along server updates to other switches in the vtp domain... but they won't use the update themself.

The 0.0.0.0 is because the update wasn't accepted (because of transparent, or different domain name, or because its an Older Boson NetSim that does the 0.0.0.0 even when it shouldn't -- not sure about the newer NetSims).

Don't forget to spend some time on other topics -- but yeah, STP and VTP should be easy points on the exam once you understand it.

Remember that the Simulator(s) isn't(aren't) always right.

So don't lose study time because of inconsistent or wrong simulator results.

ceejay3001

cheers mate - you are right about the vtp question.

another question
same topolgy

what is the root bridge for vlan 1

how do i do this
sh span tree identified the root port
sh cdp neighbor indentifies the root port going to the neighbor switch

but how does this prove the neighbor it goes to is the root switch

ceejay3001

mikej412

ceejay3001 wrote:

what is the root bridge for vlan 1

how do i do this
sh span tree identified the root port
sh cdp neighbor indentifies the root port going to the neighbor switch

but how does this prove the neighbor it goes to is the root switch

Back to STP -- good -- because now I'm thinking maybe I was wrong before about the switch opposite the root bridge having the blocking port.

Okay -- if you can only access the console of one random switch and you do a show spanning-tree.....

1. it is the root bridge, it says its the root bridge, and the root ID matches the bridge ID, and no ports are blocking.

2. if it does have a port thats blocking, then its not the root bridge, but the root id and bridge id woudn't match anyways.... and it already didn't say it was the root.

show spanning-tree should show for each port, the designated bridge id (?) ..... if the designated bridge id matches the root id, you are directly connected to the root bridge (switch) (?)

If you are the switch that isn't connected to the root bridge... what do you see for each port in the show spanning-tree command? The bridge id of the switch you are connected to?

I tried 3 Network Simulators -- 1 doesn't support spanning-tree, and the other 2 were inconsistant and in one case, displayed wrong information. I keep remembering over and over why I gave up on the network simulators....

Again -- this sounds like a job for 4 real switches? Anybody? Show us some real output!

ceejay3001

ive cracked it now as i managed to set this up on boson.

you was along the right path for definite in terms of finding out whats directly connected --cheers bud

David_HX

ceejay said: "" how do i do this
sh span tree identified the root port
sh cdp neighbor indentifies the root port going to the neighbor switch ""

I always thought that the 'Root Port' *from* any Switch *always* was connected directly to the Root Switch., hence the name, "Root Port".

So what is the answer and how did you derive it ceejay ?

DvD