Best Practice question...

Unanswered Question
Jul 2nd, 2008

Right, lets open this one up for discussion...

We have a series of 100Mbps links that connect the various sites at our University across town up.

Each site has its own complement of VLANs and we use OSPF to route between all of the sites.

We currently use a mixture of 3550, 3750 and 3560 switches to handle the routing. Would it be better to replace these with a small router, maybe a 2800 series to look after the routing between sites and have switches off the back of these? Is there any advantage to doing this? Also, money is no probloem at the moment :-)

Opinions would be greatly received!



I have this problem too.
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cisco_lad2004 Wed, 07/02/2008 - 04:17


hard to give a straight reply :-)

usually I woudl recommend changes when you need new features, more reliability, redundancy etc.. or when teh reuirement is imposed on you by an end of sales of a sepcific product.

My asvice is that you list your priorities and what you aim to achieve. adding a 288 and use a 3560 as a port aggregator is fine, but you are introducing another single Point of failure in your set up....unless your busget is so good, you can afford to buy 2 sets as backup :-)

so i guess the answer depends on what you aim for.



jonathanaxford Wed, 07/02/2008 - 04:21

Completely agree, its basically because the boss has lots of money to spend and is under the impression that the performance will be better.

I am thinking that the switches are more than adequate for the job. What we want to acheive is a standard setup for each site...

Basically looking for a killer reason to do this, and if there isn't one....

My argument against at the moment is that we are just adding more kit for the sake of it.

royalblues Wed, 07/02/2008 - 04:34

Unless you plan to do any encryption, Natting etc, i dont think there is any need for a router in your design

The exisitng setup should be fine


andrew.burns Wed, 07/02/2008 - 04:43


A couple of things might be useful, the main one being netflow. If all your WAN links use routers you can get some pretty good network accounting info (and there are open source netflow analysers available).

Another possible advantage is being able to add functionality with modules rather than additional devices. E.g. you could add an IPS module into a 2800 router, or a Content Engine module (for caching) or add cards for backups links such as DSL or GSM.

There are a whole bunch of IOS features supported on a router that are not supported on those switch platforms but netflow has to be the main one - I've installed routers in the past purely to get netflow.

One last but important point - most routers don't have the performance of the L3 switches and I think you'd need at least a 2851 to drive a 100Mbps link to full capacity.



Pravin Phadte Wed, 07/02/2008 - 05:05


The network setup does not seems to be changed unless you need some fetures which the switch cant handle.Also keeping in mind for future if there would be any high end implementation in the network then you can possibly think of getting the set up as above.

A 6500 also can be used but is that what you want for the network ?

I guess this is a campus network and should be working fine without nay problems if there is a high end router to handle the wan links.

Only things that need to be if the boss has money to upgrade the 3550. Remove the mixed swithes and make a standard of a single swith model and ios on the borard.

As said above it can be possibily of why you need an upgrade of all the eol eos swithes will it help. i would say yes if needed these swithes can be used on access layer.



jonathanaxford Wed, 07/02/2008 - 05:54

Thanks for all the info everyone, this is all good stuff.

Netflow is quite appealing to us, we are currently experimenting with it on a couple of 3800 routers and 6500 switches, so that is a good reason to go for routers on the WAN links...

I will let you know the outcomes once i report back to the boss!



Joseph W. Doherty Wed, 07/02/2008 - 10:53

As Andrew noted, small software routers usually only offer a fraction of the performance of a small L3 switch. For 100 Mbps, duplex, I would recommend a minimum of a 3845, if you want to be able to push line rate.


The pps wire rate for 64 byte packets at 100 Mbps, simplex, is 149 Kpps. For comparison a 2811 offers a CEF forwarding rate of 120 Kpps, 2851 220 Kpps, 3825 350 Kpps, 3845 500 Kpps; while even the small 3560-8PC offers 2.7 Mpps.


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