Cable from VLAN 1 to VLAN 2: Latency introduce

Unanswered Question
Aug 21st, 2008


I am little bit confused about this. My friend proposed the scenario like given below using a single switch.

port 1 and 2 in the vlan 1

port 3 and 4 in the vlan 2

port 1: Machine A

Port 3: Machine B

port 2 (VLAN1 )--> Latency-Calculator/generator-Machine --> Port 4 ( VLAN 2).

this is without routing.

so when machine A communicate to the machine B, traffic passes from VLAN1 (port 2) to VLAN 2 (port 4). we have tested this one and it works fine.

I have just a single question, is there is any problem in this scenario when there are lot of traffic, any spanning tree problems or any known vulnerability. I want to know coz we are going to deploy in a very large scale and in the future if it is problem then this will be great loss.

Please give me your suggestions.



I have this problem too.
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satish_zanjurne Thu, 08/21/2008 - 02:26

HI Can you upload the switch configuration where you have connected these all 4 hosts in 2 VLAN's ??

t4tauseef33 Fri, 08/22/2008 - 03:59

its a simple configuration like that

int gig 1/0/1

description Machine A

switchport access vlan 1

int gig 1/0/2

description cable connected to port 4

switchport access vlan 1

int gig 1/0/3

description machine B

switchport access vlan 2

int gig 1/0/4

description Cable conencted to port 2

switchport access vlan 2


machine A has IP

machine B has IP

both are able to communicate while in different vlans but of same subnet due to cable in the vlans.

Jerry Ye Sat, 08/23/2008 - 19:53


In general, it is not recommended to bridge 2 L2 VLAN's together.

Just a question, what kind of network topology you are trying to create? I am interested the one you mentioned "in large scale".



t4tauseef33 Sun, 08/24/2008 - 05:05

actually we have a different set of networks for each solution. and for each solution we have a test environment

For solution A we have deployed the 4 ASA 5540 FW's with 8 3750 switches with 2*2 gig LES, 4 lease lines with 4 3600 routers and lot of servers in 2 DC's

we want to create the test environment for that but donot want to spend the same amount of money as on solution A. so that's why we want to use only 1 single switch and to represnet lease lines and LES infrastructure, we want to create the lateny as present in solution A. Servers in a single vlan when communicate to other servers in the same vlan comunicate, they are switched in the hardware. so we are going to deploy the same vlan as the 2 vlans and introduce a latency box in between them to test the applications as they reside in the solution A. too complicated. This type of test scenario we are using for the first time and if is successfull then we will deploy more

Jerry Ye Sun, 08/24/2008 - 07:37

I see. But it is really hard to get some realistic results with 1 switch because the latancy between 2 switch port is minimal.




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