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wuh
New Member

ISL trunk with a pc connecting on it.

I just read a post where one of you said if a pc connects to a switch port that is configured as ISL trunk, it should be isolated.

I just did a test about this. The PC can ping the gateway that is on the siwtch it connects to. The port is ISL trunk.

is this test result reasonalbe? or am i missing something here?

Thanks!

interface FastEthernet0/1

switchport trunk encapsulation isl

switchport trunk allowed vlan 1

switchport mode dynamic desirable

end

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Silver

Re: ISL trunk with a pc connecting on it.

Hello Han,

when I mentioned an ISL trunk I was meaning a port that is a trunk always not as a result of DTP negotiation

try the following

int fas0/1

switchport mode trunk

in this case the port is always a trunk and doesn't need to negotiate a trunk using DTP (another Cisco L2 protocol) like in your config. The PC doesn't asnwer to DTP messages and the port reverts to mode access

In your scenario if you use

sh int fas0/1 switchport

you should see

admin state : trunk or dynamic desirable

operational state: access port

your port should act as an access port in Vlan1 and as a result of this the PC is not isolated and can ping the default gateway on Vlan1.

Hope to help

Giuseppe

3 REPLIES

Re: ISL trunk with a pc connecting on it.

Hi

its because u have made the allowed vlan as 1 on the port which will be the default vlan.

As u r management IP configured under VLAN 1 SVI it should be able to ping it.

Thanks

Mahmood

Hall of Fame Super Silver

Re: ISL trunk with a pc connecting on it.

Hello Han,

when I mentioned an ISL trunk I was meaning a port that is a trunk always not as a result of DTP negotiation

try the following

int fas0/1

switchport mode trunk

in this case the port is always a trunk and doesn't need to negotiate a trunk using DTP (another Cisco L2 protocol) like in your config. The PC doesn't asnwer to DTP messages and the port reverts to mode access

In your scenario if you use

sh int fas0/1 switchport

you should see

admin state : trunk or dynamic desirable

operational state: access port

your port should act as an access port in Vlan1 and as a result of this the PC is not isolated and can ping the default gateway on Vlan1.

Hope to help

Giuseppe

wuh
New Member

Re: ISL trunk with a pc connecting on it.

Giuseppe:

thanks, that makes sense to me. I misunderstood your post.

Han

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