CCNP Lab Part 2: How Badly Do You Need an L3 Switch?

The single biggest cost for gear for a CCNP lab will be the cost of a layer 3 switch - assuming you really need one. Of the four CCNP exams, only the BCMSN exam requires a lot of LAN switch features. So, today, I'll examine the LAN switching features included on the BCMSN exam, and consider whether you really need a layer 3 switch or not.

First, let's break down the list of BCMSN exam topics. Here's a list with enough detail to make the discussion robust, separated separated by whether the feature is a layer 3 feature or layer 2:

Layer 2: VLAN, VLAN trunking, Etherchannel, STP, RSTP, MIST, RPVST, switch security features, LAN QoS, wireless clients, switch IP phone support

Layer 3: Layer 3 switching, EIGRP, OSPF, HSRP/GLBP/VRRP

To be honest, some features cover both layers 2 and 3. I've organized the above based on whether the features require a layer 3 switch (eg 3550/3560 with EMI software), or not. For example, Dynamic ARP Inspection is one of those switch security features, and in theory ARP includes part of layer 3, but you don't need an L3 switch to get DAI. Likewise, 2950/2960's with Enhanced images can mark the IP header's DSCP field, which is clearly layer 3, but the switches themselves do not forward packets at layer 3.

Next, consider the listed features that require a layer 3 switch.

  • 1. Layer 3 switching - To configure layer 3 switch, you create multiple SVI interfaces commands like "interface vlan 3" to give the switch multiple layer 3 interfaces, much like a router has to have interfaces connected to each local subnet.
  • 2. EIGRP and OSPF - both configure identically on layer 3 switches as they do on routers.
  • 3. HSRP/GLBP/VRRP - no differences in configuration on layer 3 switches as compared to routers; all three are supported on router platforms as well. You can even use them on 2610's (non-XM), which are pretty cheap on Ebay.
  • 4. Private VLANs - there are some Private VLAN mapping intricacies that require the VLAN interfaces on the L3 switch, but the configuration beyond what can be done on a layer 2 switch is not significant, and can probably be understood by reading.

In short, of all the BCMSN configuration features, the only things that can't be configured using another non-L3 switch or another router are layer 3 switching itself, and maybe a few small items like the extra mapping for private VLANs.

So, let's consider general prices for a moment. I didn't look hard yet on Ebay - I'll save that for once I converge on a few examples - but from the CCNA series research, it seems that you can get a 3550 SMI for around $650, a 2950 with Enhanced image for about $300, 2950 standard image for about $200. The 3550 SMI can be upgraded to the EMI image. As usual, the standard disclaimer applies - it's up to you to figure out if your company can upgrade the switch legally or not. Now think about those price differences in light of the above comments about the difference in what you get. In particular, the 2950's with the Enhanced image should support everything else you'd need to configure for practicing BCMSN topics.

So... is an extra $350 per switch worth it to you? Let me know what you think. Next post, I'll compare the 2950 standard vs enhanced in light of the BCMSN topics, and maybe even fold in a few words about router Etherswitch modules. And don't forget to weigh in on last week's survey about how much budget to spend!


Copyright © 2008 IDG Communications, Inc.

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