turn part of the cisco switch into a plain switch

Hi

I would like to turn a few switchports of my 3560 into a completely separate
dummy plain switch. Is it possible?
I have configured a few ports to be no access vlan. Devices connected in
these ports are able to ping each other.
However, devices connected in these ports are not able to ping the devices
connected in ports that have assigned vlans. This makes the switch
configuration not equivalent to a separate dummy plain switch. How to make
the separation possible?

Thanks

 

Ports configured as access ports default to vlan 1 unless they have been
assigned to another vlan. Configuring "no switchport access vlan" puts then
into the default vlan ... vlan 1. Hosts connected to those ports can ping
each other because they are in the same vlan and cannot ping hosts in other
vlans ... as you would expect from a 'dummy plain sitch'.

What switching rules do you expect?

BernieM

 

Hi Bernie
Thanks for your reply.
But I have used no access vlan 1 for that switchport, is it still in vlan 1?
If the devices are in VLAN, then it is not a dummy switch.
It is because the packet will first try to find its default VLAN interface.
A dummy switch is just like a physical layer switch with CLI control. Just a
little bit more than a piece of cable.
Is it possible?
Thanks

 

You want say 4 ports to act as if they were on their own independant dummy
switch, right ?

Then you put those 4 ports into their own vlan (say vlan 7). Then any/all
traffic that is sent into any of those 4 ports will only ever go to those 4
ports, just like it was in its own switch.

Broadcasts sent by a device connected to one of those 4 ports will only go
to the other 3 ports on that VLAN.

The would be a hub then.

A hub transmits all information from all ports to all ports.
A switch learns the ethernet addresses of devices connected to each port,
so a unicast to a known ethernet address gets sent to only that port.


I am not certain you could turn all 4 ports into a "hub". But you can make
one port listen in on the remaining 3 with port mirroring. This way, one
port would see all the traffic sent/received by the other 3 ports. (acting
a bit like a hub).

 

You may have used "no access vlan 1" but does that appear in the config? A
switchport by default is in vlan 1 but "switchport access vlan 1" is one of
those default settings that doesn't appear when you do a "show run".

What do you mean by a dummy switch. By default all ports on a switch are in
the same vlan but not 'on the same piece of wire'. As JF Mezei explained
that's the difference between a switch and a hub. For the switch to act
like a hub you'd have to disable the 'mac-address table' function so all
packets get transmitted out all ports. Is this what you're expecting?

What do you mean by "the packet will first try to find its default VLAN
interface"? Frames coming from the servers and frames coming from the
switch, on an access port, are not vlan tagged.

BernieM

 

If you dont what to ping each other or specific ping is required, use PVLAN concept. ISP does use this concept in there domain.