Unanswered Question

I am replacing a failing 4500 switche with a newer 4500. This should have been easy but the old switch is using CATOS and the new one has IOS installed. I am slowly recreating the config but have come across something I am not sure about. I have the following line set port channel 2/1-4 183 in the old config. As far as I can see this is aggregating interfaces 2/1-4 is this correct? What does the 183 mean is it just an identifier?

In the router part of the config I have interface Port-channel1.2 and this has an IP address and 802.1q set if I do SH VLAN I can see that this is vlan 2. Can I just use interface vlan 2 and assign it an IP address in IOS?

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Jon Marshall Sun, 07/22/2007 - 08:14

Hi Tim

Set port channel 2/1-4 183 is indeed aggregating ports 2/1-4 into an etherchannel. The 183 is the admin group which is an identifier between 1 and 1024 and is an optional value.

With IOS you would just create a vlan 2 interface and assign it the IP address as you say. Obviuosly make sure the vlan exists at layer 2.



Pavel Bykov Mon, 07/23/2007 - 00:00

IOS equivalent of those commands are (assuming the port is trunk):

interface range Fa (or Gi) 2/1 - 4


channel-group 1 mode on

no shutdown

interface po 1


switchport trunk encapsulation dot1q

switchport trunk allowed vlan XXX,YYY,ZZZ...

switchport mode trunk

Fa or Gi depending on interface type. You can ignore "183", as per Marshall

Jon Marshall Mon, 07/23/2007 - 00:14

Hi Pavlo

I'm not sure the above config will achieve the same thing. Tim said that the port-channel was po1.2 and had an IP address assigned to it. If that's the case it is acting as a Layer 3 interface so he will need to create a layer 3 SVI on the new 4500.

The config you supplied will only create a layer 2 etherchannel.



Amit Singh Mon, 07/23/2007 - 01:31


The config pasted by the original poster was indeed for layer 2 ether-channel only. Cat4006 was layer 2 switch only with Sup2 running CatOS.As mentioned there was router card on the chassis which was 4232-L3 and was used for inter-vlan routing across the switch. I think the port-channel interface that the original poster was referring was only for inter-vlan routing across the switch backplane. It was a requirement for creating a port-channel on the internal gigabit ports between the sup and the routercard across backplane for interlvlan routing.

Please see the link below:


-amit singh

Jon Marshall Mon, 07/23/2007 - 01:48

Hi Amit

Okay now i am confused. I have used the 4006 switch in this mode before and an aware of having to create a port-channel interface for inter-vlan routing.

But isn't that the whole point. If there is a po1.2 with an ip address this means that there must be inter-vlan routing happening on the old 4006. So to replicate that onto the new 4500 with IOS you have to create a layer 3 SVI ??


Amit Singh Mon, 07/23/2007 - 02:28


Agree, with you on this. Yes, for inter-vlan routing, layer3-SVI's need to be created.

-amit singh

Thanks for the replies. I have created VLAN interfaces and the routing table is popuplated so I think that side is working OK. I need to start tracing fibre cables to work out what interfaces I need to confiure etherchannel on.

One thing I have noticed is that when I plug my laptop into the switch I get a DHCP address assigned by it with an IP address in the same range as the first VLAN. As far as I can see there is nothing in the config that mentions DHCP is this normal.


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