join switch ports together

Unanswered Question
Nov 25th, 2009

cisco 2651XM router

IOS: c2600-adventerprisek9-mz.124-15.T9.bin

NM-16-ESW switch fitted

regarding the switch ports (F1/0 to F1/15):

is there a command that will join two or more switch ports together and make them act as plain hub ports?

I have this problem too.
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Leo Laohoo Wed, 11/25/2009 - 13:30

"join two or more switch ports together"
You mean etherchannel?  Yes, it's supported.


"make them act as plain hub ports"
Hub ports?  Can you please elaborate?  Otherwise you can put/assign two or more ports into a VLAN.

tonyspcrepairs Wed, 11/25/2009 - 13:48

the ports in question are already on the same vlan, but I want them to behave as plain hub ports and not switch ports.

LordFlasheart Thu, 11/26/2009 - 05:14

I'm not sure I catch your drift here. Ports in the same VLAN are in the same broadcast domain a la a hub albeit not in the same collision domain.

tonyspcrepairs Thu, 11/26/2009 - 06:31

yes that's it, I want two or more ports in the same collision domain, just like a hub.

Nagendra Kumar ... Thu, 11/26/2009 - 08:44

Hi,

On a switch, each port will be in a different collision domain. This is one maj

Do you have any specific reason to have 2 ports in same collision domain?.

Regards,

Nagendra

tonyspcrepairs Thu, 11/26/2009 - 08:49

yes I do have a reason.

is there a command that will join two or more switch ports so they are in same collision domain? - like a hub?

Leo Laohoo Thu, 11/26/2009 - 13:41

I have no idea about the others but I still don't know why you want a Layer 2 switch to behave exactly like a Layer 1 hub.  How about connecting both ports to a hub?  Are you trying to set up packet sniffing?

tonyspcrepairs Fri, 11/27/2009 - 04:43

yes I am currently using the monitor command on the router to sniff packets on a port, but I'm only allowed one monitor session at a time on my platform so I can only sniff one switch port at a time. I've got a PC running wireshark connected to the monitor destination port for packet sniffing. I know I could use a hub to sniff multiple ports but it would be more convenient if I could do away with the hub and sniff multiple ports from the NM-16-ESW switch I'm using.

LordFlasheart Fri, 11/27/2009 - 04:51

monitor session 1 source vlan x

That should do you on multiple ports in the same VLAN.

Or monitor session 1 source int fa 0/1, 0/2, 0/3 if you want to tie down particular ports.

tonyspcrepairs Fri, 11/27/2009 - 07:01

thanks for your response, but I can't get those commands to work.

router(config)#monitor session 1 source vlan 1
SPAN Source Vlan is not supported in this platform

router(config)#monitor session 1 source int fa 0/1, 0/2, 0/3

doesn't work either. It doesn't recognise the commas, doesn't recognise spaces, doesn't seem to allow more than one port to be specified - unless I'm doing it wrong.

if I query what's available this is what I get:

router(config)#monitor session 1 source int ?
  FastEthernet  FastEthernet IEEE 802.3
  Port-channel  Ethernet Channel of interfaces:

there doesn't seem to be any way to choose multiple ports.

tonyspcrepairs Fri, 11/27/2009 - 07:55

hang on I think I might have got it. I had no idea there were more configs available after the FastEthernet number. This command appears to have done the trick:

router(config)#monitor session 1 source int fa 1/14 - 15

I can now sniff traffic on the these two ports.

I originally tried sniffing four ports (12 - 15, to include my cisco ip phone) but this seemed to knock the phone out. The above command seems to work for a range of ports but I still haven't worked out how to select specific ports.

Jon Marshall Thu, 11/26/2009 - 14:43

tonyspcrepairs wrote:

yes I do have a reason.

is there a command that will join two or more switch ports so they are in same collision domain? - like a hub?

It's not 20 questions. The reason you were asked why you wanted to do it was that there might be a different way to achieve what you want.

Can a switch act as a hub - sure, a switch can only hold so many mac-addresses in it's cam table and if the cam table is full then it has to flood all packets to all ports. So just get typing with the mac-addresses

Jon

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