I’ve been meaning to post this for some time. Awhile back there was a thread on Networking Forum where someone mentioned that 2960s can route now. The 2960 is now a layer 3 switch. I was skeptical, but then I was pointed to this link. I was very, very surprised. I’m not sure why Cisco decided to add this functionality to the 2960s, but I’m definitely grateful. As of 12.2(55)SE, 2960s are layer 3 switches (with some limitations which I’ll cover later). This knowledge came in handy shortly after reading that thread. I was working on a circuit upgrade for a remote side at my previous company. The circuit was ordered incorrectly and I ended up in need of a layer 3 switch ASAP. The tech we’d sent was leaving the next day, so there was no time to ship him anything. Luckily, we had some 2960s on site.

 

Configuring 2960s to route is pretty simple. The Switch Database Management template (SDM) needs to be changed to “lanbase-routing”. A reboot is (always) needed after changing the SDM template. After reboot, it’s just like enabling routing on any other L3 switch with the command “ip routing” from global config.

 

First we’ll change the SDM template:

SwitchA(config)#sdm prefer lanbase-routing
Changes to the running SDM preferences have been stored, but cannot take effect until the next reload.
Use 'show sdm prefer' to see what SDM preference is currently active.
SwitchA(config)#^Z
SwitchA#reload
System configuration has been modified. Save? [yes/no]: y
Proceed with reload? [confirm]

After changing the SDM template, we are reminded that we’ll need to reboot and also given a command to verify the change after the next boot.

 

Now we verify:

SwitchA#show sdm prefer
The current template is "lanbase-routing" template.
 The selected template optimizes the resources in
 the switch to support this level of features for
 8 routed interfaces and 255 VLANs. 
  number of unicast mac addresses:                  4K
  number of IPv4 IGMP groups + multicast routes:    0.25K
  number of IPv4 unicast routes:                    4.25K
  number of directly-connected IPv4 hosts:          4K
  number of indirect IPv4 routes:                   0.25K
  number of IPv4 policy based routing aces:         0
  number of IPv4/MAC qos aces:                      0.125k
  number of IPv4/MAC security aces:                 0.375k

The change was successful and we’re given the details about this SDM template.

 

Now seems like a good time to touch on the limitations of the layer 3 capabilities on 2960s. As we see in the output above, we’re limited to 8 routed interfaces. These will be SVIs. At this point, the 2960s don’t support routed physical interfaces (“no switchport”). Another important note is that we’re only allowed 16 static routes and there is no dynamic routing capability.

 

Now we’ll enable IP routing and configure a couple SVIs:

SwitchA#conf t
SwitchA(config)#ip routing
SwitchA(config)#
SwitchA(config)#int vlan 15
SwitchA(config-if)#ip add 192.168.15.1 255.255.255.0
SwitchA(config-if)#
SwitchA(config-if)#int vlan 25
SwitchA(config-if)#ip add 192.168.25.1 255.255.255.0
SwitchA(config)#^Z
SwitchA#sh ip route
...
C    192.168.15.0/24 is directly connected, Vlan15
C    192.168.25.0/24 is directly connected, Vlan25

Even now, I’m still amazed that we can do this with a 2960. As expected, it’s working. We have two SVIs and we can see the routing table reflect this.

 

As you can all see, I’m still pretty wowed. There are many scenarios where layer 3 2960s could be useful.

Colby

Colby Glass has been in IT since 2002. He is currently a Systems Engineer (presales) with a Cisco Gold partner and holds the CCNP R/S, CCNP DC, CCDP, CCIP, JNCIA-ER.

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