SDM: 3750 Question

Unanswered Question
Aug 19th, 2009

Hi,

I am trying to understand how far can 3750 support SVI. According to the default SDM, it can only support 8 routed interfaces. I am trying to identify what does it mean by that. That does refer to routed port only or both routed port and SVI? Also, what if I create more than 8 SVIs? Will that be an issue? Thanks.

3750#sh sdm prefer

The current template is "desktop default" template.

The selected template optimizes the resources in

the switch to support this level of features for

8 routed interfaces and 1024 VLANs.

number of unicast mac addresses: 6K

number of IPv4 IGMP groups + multicast routes: 1K

number of IPv4 unicast routes: 8K

number of directly-connected IPv4 hosts: 6K

number of indirect IPv4 routes: 2K

number of IPv4 policy based routing aces: 0

number of IPv4/MAC qos aces: 512

number of IPv4/MAC security aces: 1K

John

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Yudong Wu Wed, 08/19/2009 - 09:52

You can configured more than 8 SVI and physical routed interface. But the switch performance is optimized on 8 routed interfaces, such as TCAM resource. If you configure more, the switch might have performance issue.

John Patrick Lopez Wed, 08/19/2009 - 09:58

So what they are saying here is routed interfaces both includes routed ports and SVI? Like for example I can do 4 routed ports and 4 SVI. Then adding another SVI might cause performance issue.

I also saw this note from Cisco's website which says.

"If the switch attempts to boot up with a configuration that has more VLANs and routed ports than hardware can support, the VLANs are created, but the routed ports are shut down, and the switch sends a message that this was due to insufficient hardware resources. "

I am afraid that it might happen.

Thanks.

jbrenesj Wed, 08/19/2009 - 10:29

"The number of routed ports that you can configure is not limited by software. However,

the interrelationship between this number and the number of other features being

configured might impact CPU performance because of hardware limitations."

Basically, per development, the number 8 that is specified is a conservative number

recommended based on the acceptable tested limit when all configurable features are

enabled. More than 8 routed interfaces are supported but lots of duplication of TCAM

entries can occur per routed interface especially with hundreds of multicast groups or

lots of other features.

As you can see, this only refers to the L2 ports that you can configure as L3, but this

does not mean that you can only use 8 policies as you can always apply them to a VLAN

interface.

John Patrick Lopez Wed, 08/19/2009 - 11:31

Yes I understand what you are saying. What I am asking was if the number mentioned there was a combination of routed "port" and SVI.

Because the switch output says "routed interface".

Thanks.

jbrenesj Wed, 08/19/2009 - 11:42

To answer your specific question, yes we optimise the performance to 8

routed (SVIs and Phy) interfaces "combined"

There were some internal testing done with this platform and although I

cannot publish the details I can confirm that actually you will not see any problem and the switch will function correctly under a greater number of SVIs (128), but with the routing "template". Anyhow, if you plan to use this 3750 for routing, L3 ports, SVIs and some routes in the table you may want to switch to the routing sdm template

John Patrick Lopez Wed, 08/19/2009 - 14:23

Hey thank you so much for this information. I will just leave the sdm template to default since it doesn't increase the supported routed interface anyway.

Do you suggest going beyond 8 interfaces? Thanks.

jbrenesj Wed, 08/19/2009 - 14:45

Well, that's hard to answer, I guess it all depends on what you need the 3750 to take care of (in terms of routing) but I have certainly seen these switches performing well with a couple more L3 interfaces.

So it seems that you won't need the routing template unless doing PBR or handling a huge routing table like BGP.

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