Difference between SMI or EMI

boile · June 2010

Hi
I was planning to buy some Cisco 3550 or 2950 switches. However, Could not figure out which one is better for CCNP/CCIE. There are too many choices for me to buy.

I believe, since 3550 does Layer-3 routing, it is better for me if I go for cisco 3550 switches. I believe, I should invest my money for the switches with EMI images.

Now, the problem is, I have found the following switches on ebay. And These are my understanding.

I guess some of them already have EMI images, however, some of them were built for SMI, but then the sellers have installed EMI.

Then some people said, the switches built for SMI, does not support the EMI properly (because of the RAM issue).

I am really confused. It would be nice if someone can explain them further, or correct them if I am wrong.

* Cisco Catalyst WS-C3550-24PWR-SMI PoE 3550 24 With EMI

????

* CISCO Catalyst WS-C3550-24-EMI Switch 3550 24 Ports
????

* Cisco WS-C3550-48-SMI 3550 48 PORT SWITCH W/EMI QTY

????

wastedtime · June 2010

I haven't heard anything about the ram issue with 3550s like that, but here was a post on the SMI vs EMI: http://www.techexams.net/forums/ccnp/37135-3550-emi-vs-smi.html

Also check the cisco link in there as it does a pretty good job in explaining the difference.

Jason0352 · June 2010

FYI, if you download an IOS image that contains both SMI and EMI options, depending on the model number of the switch determines if the EMI gets copied to flash or SMI.

I just downloaded a 2950 IOS that had both and it only installed the SMI since my 2950's weren't made for the EMI option.

EMI has QoS options and a couple other routing improvements over the SMI.

phantasm · June 2010

In short an EMI image is capable of routing (layer 3 switch) whereas a switch with an SMI image is layer 2 only (cannot route).

boile · June 2010

Jason0352 wrote: »

I just downloaded a 2950 IOS that had both and it only installed the SMI since my 2950's weren't made for the EMI option.

How do I exactly know, if the switch were made for the EMI option?

wastedtime · June 2010

The 2950s are layer 2 only. They do have a standard and enhanced image, but they are hardware dependent. Here is a link that will tell you: Catalyst 2950 Series Software Feature Comparison--SI and EI [Cisco Catalyst 2950 Series Switches] - Cisco Systems

The 3550s are layer 3, both SMI and EMI and they are not hardware dependent. Check the link I provided in my last post as it tells you all the differences.

If you get a "show version" of the 3550 switch it should have EMI in the model number.

alan2308 · June 2010

And for the 2950's, over time the differences between EMI and SMI have narrowed. Getting a SMI 2950 might not be so bad. Take a look at this. It was written with a CCNP lab in mind, but the point on the different 2950 models is still valid here:

The Best Switch for CCNP Prep in 2010 | NetworkWorld.com Community

boile · June 2010

wastedtime wrote: »

I haven't heard anything about the ram issue with 3550s like that, but here was a post on the SMI vs EMI: http://www.techexams.net/forums/ccnp/37135-3550-emi-vs-smi.html

Also check the cisco link in there as it does a pretty good job in explaining the difference.

Thanks a lot for the link. So,

I believe I should ask the seller to give me a "sh ver" output. And if it has EMI, I can buy that.

wastedtime · June 2010

boile wrote: »

Thanks a lot for the link. So,

I believe I should ask the seller to give me a "sh ver" output. And if it has EMI, I can buy that.

If you want to make sure that you are getting a EMI model then yes. As other people have said though a SMI model with the EMI image would work just find.

miller811 · June 2010

phantasm wrote: »

In short an EMI image is capable of routing (layer 3 switch) whereas a switch with an SMI image is layer 2 only (cannot route).

Cisco Catalyst 3550 Series Switches [Cisco Catalyst 3550 Series Switches] - Cisco Systems

There is support for basic IP unicast routing via Static Routes and Routing Information Protocol (RIP) Versions 1 and 2 using the SMI. The EMI provides advanced IP unicast and multicast routing. These advanced routing protocols are Open Shortest Path First (OSPF), Interior Gateway Routing Protocol (IGRP), Enhanced Interior Gateway Routing Protocol (EIGRP), Border Gateway Protocol Version 4 (BGPv4), Protocol Independent Multicast (PIM), and PBR.

Q. Is the EMI required to allow Layer 3 and Layer 4 lookups for QoS and security?
A. No. Both the SMI and the EMI allow for Layer 3 and Layer 4 lookups for QoS and security.

Q. What features are only supported on the EMI?
A. The following features and functionality are only supported with the EMI:
• Advanced IP routing protocols for load balancing and constructing scalable LANs:

– OSPF

– IGRP and EIGRP

– BGPv4

• WCCP to allow switch interaction with a cache for the purpose of redirecting content requests to a cache and performing basic load balancing across multiple caches

• PBR to allow specific policies to be implemented by causing selective traffic to take different paths

• PIM for IP multicast routing within a network that enables the network to receive the multicast feed requested and for switches not participating in the multicast to be pruned; support for PIM sparse mode (PIM SX), PIM dense mode (PIM DX), and PIM sparse-dense mode

• Distance Vector Multicast Routing Protocol (DVMRP) tunneling for interconnecting two multicast-enabled networks across non-multicast networks

Difference between SMI or EMI

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