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Cisco 2948G-L3 as a normal Layer 2 switch?

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Nov 13th, 2010
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I have a Cisco 2948G-L3 switch with cat2948g-in-mz.120-7.W5.15d.bin. I need to use this switch as a normal layer 2 switch.

We already have another Cisco 3560 layer 3 switch with all vlan's configured and I need to use this 2948G-L3 as an edge switch for a vlan from 3560.

I connected the Uplink from cisco 3560 to  an ordinary linksys layer 2 switch instead of this cisco 2948G-L3 and there is no issues with the connectivity, but its not working while I use 2948G-L3 switch instead of linksys switch. I gave no shut on all interfaces of 2948G-L3. Do I need to disable/enable anything in Cisco 2948G-L3 to make it act as an ordinary L2 switch?

Thanks for any help.


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deyadav Sat, 11/13/2010 - 22:38
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Hi Ribin,

This is a way too old switch and I have never worked on it, yet, reading through it's documentation, it looks strictly L3.


The following general guidelines apply to all physical and virtual interface configuration processes.

  • Each interface must be configured with an IP address and an IP subnet mask.

  • The virtual interfaces supported by Cisco switch routers include subinterfaces.

So, it might not help using it as an edge switch. You may refer to this document, to see how this switch fits in network environment:





Mahesh Gohil Sat, 11/13/2010 - 22:39
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Hello Ribin,

As you said earlier it was working as L3 Switch...now are you sure all its ports are working as L2.

You can verify port by "sh interface interface-name switchport"  and the output should be Switchport: enabled

If not you can change its behavior by putting below command

interface range fa0/1-24


Or if you want to divide it in different broadcast domain you can configure vlan as per your design in different ports

Above is general recommendation irrespective of series of switch....



ribin.jones Sat, 11/13/2010 - 23:03
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I am not able to give the command you mentioned.

Router(config)#interface ?
  BVI                Bridge-Group Virtual Interface
  Cable              CMTS interface
  Dialer             Dialer interface
  FastEthernet       FastEthernet IEEE 802.3
  GigabitEthernet    GigabitEthernet IEEE 802.3z
  Lex                Lex interface
  Loopback           Loopback interface
  Null               Null interface
  Port-channel       Ethernet Channel of interfaces
  Tunnel             Tunnel interface
  Virtual-Template   Virtual Template interface
  Virtual-TokenRing  Virtual TokenRing
  Vlan               Catalyst Vlans

Any other way by which we can make sure that it works as Layer 2?

- Ribin

ribin.jones Sat, 11/13/2010 - 23:06
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Also I am not able to give "sh interface interface-name switchport" command either. The only available options are:

Router#sh interfaces ?
  Controller       Controller Port
  FastEthernet     FastEthernet IEEE 802.3
  GigabitEthernet  GigabitEthernet IEEE 802.3z
  Null             Null interface
  accounting       Show interface accounting
  crb              Show interface routing/bridging info
  fair-queue       Show interface Weighted Fair Queueing (WFQ) info
  irb              Show interface routing/bridging info
  mac-accounting   Show interface MAC accounting info
  precedence       Show interface precedence accounting info
  random-detect    Show interface Weighted Random Early Detection (WRED) info
  rate-limit       Show interface rate-limit info

deyadav Sat, 11/13/2010 - 23:24
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Hi Ribin,

As I mentioned, probably this switch can't act as L2. You may try this command, if it's supported, which as per configuration seems like not supported:

- conf t

- int fa

- switchport

If switchport is not supported, it confirms it can't act as L2.



ribin.jones Sat, 11/13/2010 - 23:38
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Those commands are not supported.

If the switch can act as L3, it should be working on Layer 2 as well, right?

- Ribin

deyadav Sun, 11/14/2010 - 00:21
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Well you are correct, L2 support should always be there, however it cannot act as a strict L2 port, like other Cisco switches. That came as a surprise to me, however it's more about how it's aligned in the market place. Refer to the data sheet:


In a way, it's working strictly as a router.



vragotha Sun, 11/14/2010 - 01:29
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This switch should support bridge groups.

Try configuring a bridge group and assign interfaces to each bridge group to be part of the same network. This will be similar to how vlans will work. You should also be able to configure a bvi if required

ribin.jones Sun, 11/14/2010 - 01:34
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Hi all,

I got it working. Configured a subinterface and then applied bridge-group in all interfaces.

- Ribin


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