Cisco Layer 3 Switching

Posted on 2010-11-22
Last Modified: 2012-05-10

I was wondering what the difference between a Cisco 2900 router running SP Services and a Cisco 3560 layer 3 switch running SP Services (EMI) would be?
Would the switch be able to do all the same routing features as the 2900?

Question by:mark_06
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Accepted Solution

wpharaon earned 125 total points
ID: 34194649
A router provides more services such as: extensive QoS, NBAR, IPSec, Security features, BGP capabilities etc
A switch, provides greater speeds and port density, has its limitation as an edge device.
You need to examine what services this edge device will be responsible for, and make the decision based on that. Not only on speed.

Assisted Solution

ciscocert earned 125 total points
ID: 34196140
The router is a pure layer 3 device ( can perform switching with addition of Switching modules). The 2900 belong to ISRG2 its lot more efficient than ISRG1. It can support high capacity DSP for video and voice, enhancement in processors and power is managed efficiently.. And lot more functionality, it can also be used to terminate any wan connection, Supports VPN and yields security. A router is traditionally software based the routing is performed over a software. The CPU used is a general purpose CPU.
Layer 3 Switch
The traditional switches are layer2 only devices. But the switches like 3750,3770 etc can perform Routing also. The speed is also a concern here, since the switches uses specialised hardware ASIC's it can perform switching at wire speed. It can perform dynamic routing like routers do.

Every device has its place a l3 switch cannot perform all the functions a router have and it depends on where you are using and for what you are using for. For example it you are doing an intervlan routing the L3 switch seems better to do it than a router( router on a stick).
You will not ger all the features in both the L3 switch and router to be same. You can use cisco ios navigator to find the features supported.

Author Comment

ID: 34196207
thanks for your replys. I am looking for the following features - PPP termination (auth with radius), ACL's,VLans and speed!
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Author Comment

ID: 34196211
And also BGP
LVL 50

Expert Comment

by:Don Johnston
ID: 34196547
You'll need a router to get those features.
LVL 79

Expert Comment

ID: 34196954
Agree with donjohnston, you need a 2900ISR router and not a switch.
Speed is irrelevent when you are talking connection to a WAN link. I doubt that you are getting more than 1Gb bandwidth?  Probably more like 10Mb max? You need something that does queueing very well going between 1G lan speed and much slower WAN link speeds. Job for an edge device (router, not switch)
Terminating PPP connections is a job for an edge device. As an edge device, I would assume that you also need to NAT? If yes, then a switch cannot do NAT (unless you get a big honkin' 6500)..

Switches are simply not designed to be Internet edge devices, routers are.
Put a L3 switch behind the router to do the full line-rate routing between VLAN's.
For the extra cost of adding EMI services licensing to a 3560G switch, you can almost buy a 2911 router and the standard services version of the switch and have them both!

Expert Comment

ID: 34198993
Yeap for sure you need a router to terminate a wan link. you could configure the vlans on the L3  and do intervlan routing with L3 efficiently. If you have a 3560 and 2900 then go ahead. Or if you have to make a decision either with switch or router. I would recommend a  switch and router as said by irmoore.

Author Comment

ID: 34201641
Thanks guys, I think I will need the switch and the router.

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