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New Member

Switch issue

If I connect connect two equipment as below. The result is I can ping the 2924 ip from 3560.

Why ? Why 2924 fast ethernet port is vlan 1 but 3560 fast ethernet port is vlan 2. the connection is also success ?

2924

Int fa0/1

!

Int Vlan1

Ip address 10.10.10.1 255.255.255.0

!

Ip-default gateway 10.10.10.254

3560

Int fa0/1

Switchport mode access vlan 2

!

Vlan 2

Ip address 10.10.10.254 255.255.255.0

5 REPLIES
Cisco Employee

Re: Switch issue

Hi Friend,

Thats a leakage in technology which you can term as VLAN Leakage. The reason WHY it is pinging is because you have access ports configured on both the switches which are connected to each other.

Now when frame comes to fa0/1 port on 2924 switch and because that port is not a trunk port but just an access port when frame moves out of that potr there is no tagging on that frame and its just a frame without any vlan information and once it reaches 3560 switch on fa0.1 and because it is configured also as an access port for vlan 2 it assigns PVID 2 for that frame and now that frame is a part of vlan 2 when it reaches 3560 backplane and is the reason your communication is working between switches.

If you configure the connection between the 2 switches as a trunk port it will not work.

HTH

Ankur

*Pls rate all helpfull post

New Member

Re: Switch issue

Then how about if 3 pc is connected to a single switch with 3 switchport and assigned to vlan 1,2,3 respectively. Can they be pinging each other ?

Re: Switch issue

HI

In that case u need to have a layer 3 device to communicate between diferent vlans.

Thanks

Mahmood

Cisco Employee

Re: Switch issue

Hi Friend,

In this situation you need to have layer 3 device doing inter vlan routing because frames from one pc is not going out of switch.

But if you have 2 switches connected to each other via access port like vlan 1 on switch one connected to vlan 2 on switch 2 and pc on vlan 1 on switch 1 will be able to ping pc on vlan 2 on switch 2.

HTH

Ankur

*Pls rate all helpfull post

New Member

Re: Switch issue

Hi Mahmood,

Thanks! I know what you mean. I just suprised that why switch can change the PVID from 1 to 2 when two switch is connected by access port

However, within a Single switch with different vlan assigned to each port (e.g. port 1 is vlan1, port 2 is vlan 2, port 3 is vlan 3.....)

then single switch has not the ability to change the PVID from 1 to 2 when port 1 want to communication with port 2

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