Impact of changing SDM-Template?

[Tony Riccardi]

Cisco Community,

Your assistance and experience in this matter would be hugely appreciated.

My client has a requirement to apply Policy Based Routing in their 3750 Stack Switch environment. In order to allow this I need to reconfigure each of the 3 effected stacks to a SDM Routing Template. However, I am concerned about the upgrade process and the impact to existing features and services already in place on each of these stacks.

There are 3 stacks that need upgraded. One of the stacks comprises of 2 x WS-C3750G-48TS switches. The other two stacks are comprised of 2 x WS-C3750G-24TS switches. All reside in the core of the network and provide the following L2 and L3 functions:

• spanning tree root for up to 20 VLANs
  
• eigrp routing
  
• multicast routing
  
• QoS policies
  
• spanning-tree rapid-pvst
  
• L2 and L3 2-port LACP etherchannels
  
• L3 SVI ports to WAN routers
  
• each switch is fully populated providing access to core production servers
  
• redistribution of local static routes via a configured route-map
  
• ntp services
  

My question is, if I reconfigure the SDM Template from the current default template to the default routing template although I will gain PBR functionality will I lose any of the above functions?

I also need to reconfigure the SDM template but attempt to offer zero-downtime. Can I apply the new template to one stack member at a time without having to bring the entire stack down during a reboot?

There are CPU peaks of up to 70% on these switches (during moments of high traffic). What is the expected hit on CPU and memory resources under the new template?

I am sifting through Cisco documentation but your real-life experiences and hands-on knowledge of the subject would be hugely appreciated.

Thank you.

[Nathan Spitzer]

  I do have a pair of 3750's with the routing template acting as internal border routers but in general I would try to avoid using 3750's like this. If you do, you probably want to ensure you have the Enhanced IOS because the standard one has enough limitations in routing itself that, IMHO, if you have to do PBR you have a good chance of bumping into them.  If you look at the documentation, by enabling the routing template, you dont loose functionality but you do loose some capacity, namely:

• You go from 6k to 3K MAC addresses. Assuming you havent gone crazy and the 20 VLANS ar /24 or less, the max MACS you should see is 5100. So you need to take a look and see how many devices are in you current MAC tables. If it is more then 3k then you are in trouble. Of course, IMHO if you are switching/routing 3K worth of devices with a 3750 stack you are already in trouble.
  
• You go from 6K to 3K directly connect hosts. Same arguments as above apply
  
• You go from 2K to 8K indirect routes - You gain the ability to have a much larger routing table.
  
• You gain the ability to do PBR
  

[Tony Riccardi]

Hi Nathan,

I am currently running c3750-ipservicesk9-mz.122-53.SE2.bin on each of the stacks, and there are no more than 500 MAC entries in the current MAC table. Do you think this will cause a problem?

I dont think that the overall capacity of each of the switch stacks should be effected although you can never predict the exact impact of making a fundamental change to the TCAM in this way.

[Nathan Spitzer]

Nope, you should be fine then.