Original subtitles

Okay so let's see if a trunk is formed between switch one and switch two.

And if a trunk is formed between switch to and switch three this is the capture between switch one and

switch two.

I'm going to do a search for DDP so I've named to the switches to make it easy to know which switch

is sending DDP messages.

Cisco switch one Cisco switch two.

So again this is the link between these two switches.

If we look at the dynamic trunk protocol.

Notice operating administer of mode is access order operating administer of ISIL negotiated so it looks

like they may negotiate to use ISIL trunk status is access auto and what I'll do is just make this bigger

so we can see the full why shock capture.

Notice trunk operating status as access trunk administrative status is order.

In other words order has been used on that switch.

Now this is switch one and I could show you that by looking at to the console of the switch so console

of switch one

show interface trunk firstly shows us that no trunks are formed.

But notice show interface gigabit 00 switch port.

What you'll notice here is this command shows the interface interface is a switch port administer of

mode is dynamic auto operational mode is static access in the y shock capture we see operating status

as access administrative mode his order said administer of mode is dynamic auto over there that's what

we see here static access is the operational mode so operating mode is access.

So at this point there's no trucking on that port the port is acting as an access VLAN in VLAN 1 as

you can see over there.

Negotiation of trucking is on but a trunk is not formed.

And as I go through the messages I mean you must be careful looking at the very first messages go and

look at the later messages to see if the state changed notice stole access order trunk type is ISIL

negotiated they would negotiate to use ISIL if one of the sides negotiated switch to is also set to

access auto so the point is notice over here DTP operating and master of mode access auto operating

administer of ISIL negotiated both these switches are using DTP I'm searching for DDP messages and we

can see DTP messages but they set to mode auto mode auto or dynamic auto as we can see here means that

that side will not negotiate to form a trunk the other side would have to initiate trunk yes switch

to show interface gigabit 00 switch port.

Notice dynamic auto that is the administrative mode operational mode is static access so they both configured

to use dynamic auto because neither of them initiate a connection to the other side they both passively

waiting basically for the other side to initiate trucking.

Trucking is not formed so there is no trunk formed between switch one and switch two I won't use the

show trunk command and switch to yet because we want to see what happens on the right hand side.

But notice here show interface trunk no trunk is formed on switch one OK so I kind of hinted at it.

What do you think is going to happen between switch tune switch three years the why shock capture between

switch to switch three all fulltime for DDP once again yes switch three messages.

Notice the difference dynamic trunk protocol access desirable operating administrative mode ISIL dot

one key.

So that's different to what we saw on the other side.

If we look at switch to on this link.

Notice trunk auto editor the one Q negotiated so a little bit different notice.

Switch to switch three.

One side is using auto the other side is using desirable.

So if I go right down to the end this is switch to trunk status is type of trunk trunk.

Value is trunk auto trunk operating status is a trunk.

Now if we go back to the other switches so this is switch to talking to switch one and we look at the

trunk status notice trunk status is access and I don't if that's confusing so let me show you on the

diagram.

So on the left hand side switch to to switch one this is the capture between switch one switch to notice

operating status is access.

This is an access port but on this side.

Notice trunk operating status is trunk that side's access right inside is a trunk.

It's become a trunk trunk administrative status is auto the side it's also auto.

But because switch three initiated the trunk notice it says desirable here a trunk was formed between

switch to and switch three so because switch three initiated the trunk because it's set to desirable

a trunk is formed we can see that once again by looking at the console of the switches.

So on switch three show interface gigabit 00 switch port.

Notice command shows administer mode dynamic desirable encapsulation used is one key operational motors

trunk it's operating as a trunk using dot one key show interface trunk we can see that encapsulation

is not one key trucking is enabled if we have a look on the other side it's a little bit different here

show interface trunk on this side it's negotiated to use dot one Q and trucking is enabled with this

side encapsulation is not one Q And the reason for that is I explicitly configured the encapsulation

as dot one Q and set it to dynamic desirable I wanted to show you a trunk that was negotiated with DTP

and using dot one Q rather than ISIL if I had not put this in the switches would have actually negotiated

to form an ISIL trunk these switches will use ISIL first and then dot one Q So I wanted to explicitly

force it to use dot one Q So they will try and use ISIL but if they can't then they'll use dot one Q

But again I've overridden that or I forced the switch to use dot one key was the side notice it could

have used ISIL or dot one Q So again on switch three if we got to go up here I noticed trunk desirable

dot one Q Dot one key where as on switch to trunk auto dot one Q negotiated so no trunk desirable dot

one Q Dot one key trunk auto dot one Q negotiated one side was forty used on one Q The other side negotiated

to use dot one key Okay so in summary left hand side doesn't become a trunk because both sides are set

to auto right hand side does become a trunk because one side was set to dynamic desirable as we can

see over there and uses dot one Q on the side show interface trunk the only trunk that was negotiated

is on gigabit 0 1 Okay how are you doing.

Are you able to answer these questions do you enjoy this please give me feedback.

Do you enjoy these kind of quiz questions.