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Should we be using router on a sick?

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Sep 27th, 2012
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We are looking to purchase new routers within our environment, the routers we are looking at one come with two interfaces. I understand we could purchase additional modules.


I was thinking of using router on a stick with vlans and bringing the connection forward to a switch. This was something which we all learnt was possible in our CCNA but it is something which is recommend in a production environment?


What could be the implication?

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Harish Balakrishnan Thu, 09/27/2012 - 23:07
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Hello John,



It really depends on the traffic and number of users are expected in this environment.  lets take an example of a small firm with 10 employees where they have a WAN back to their head office. In that enviroment there is no point in setting up a layered network architecture because cost is a constrain.


If you are upto setting up a network, where we have couple of hundreds users.and different utilities .. in that case it is good go for a Layer3 switch where you cn terminate your L3 vlans and make the router only to do internet/WAN routing.




Regards

Harish.

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singhaam007 Thu, 09/27/2012 - 23:15
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Hello John,


Its all up to you and how much money you got. But for production environment its not good idea to have this setup. It ok with small number of staff but still it has some disadvantages.

I would recommend layer 3 switches if your company can afford it. But otherwise it will work fine but you will start having issue as your company grows


http://www.aiotestking.com/cisco/2011/12/what-are-some-of-the-disadvantages-of-designing-a-router-on-stick-configuration/


please rate if this helps.


thanks

John Peterson Thu, 09/27/2012 - 23:29
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Thanks


Layer 3 switch was an option as we won't we using any o the routing features like VPN etc... But we noted that we needed ip adv to run full eigrp.


The plan was to perform router on a stick and let the router do the routing. I worked that on a gi port I could get nearly 2 sub vlans with 500mb throughput.


We only have a max of 50 users on one vlan and a few vlans for the servers.




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Harish Balakrishnan Thu, 09/27/2012 - 23:37
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Hello John,


well.. if you are expecting a 50 users + few servers, i would suggest to for a 12 port Layer 3 swiitch as the core to do the routing part and let the access switches be conncted with the core. It gives you much flexibility for future upgrades. and let the router do only the routing part.



Regards

Harish.

singhaam007 Thu, 09/27/2012 - 23:52
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Hi John,


Layer 3 will be good because it can perform the routing protocols as well. In router on stick there will be some network over head coz traffic will always travel through router where L3 can perform it on same hardware.


thanks

John Peterson Fri, 09/28/2012 - 01:04
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Thanks,


The concern is that L3 switch are pricey with full eigrp therefore thinking using router on a stick.


Also is the throughput on a L3 switch on routing same as the back plane?


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Harish Balakrishnan Fri, 09/28/2012 - 01:19
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it really varies on the model of the L3 switch and the backplace throughput is the one which get over the stack.


by the way why do you need eigrp support ?


regards

Harish.

singhaam007 Fri, 09/28/2012 - 01:39
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Layer 3 switches tend to have packet switching throughputs in the millions of packets per second (pps), while traditional general-purpose routers have evolved from the 100,000 pps range to over a million pps. Aggregate performance is one of the key differences between Layer 3 switches and traditional routers. Traditional routers still offer key features used typically in WAN environments. However, many of those features, such as multicast routing, multiprotocol routing, IBM feature sets, routing protocol stability, are still key for Layer 3 switches/campus routers.

it depends on make and model.

http://www.itworld.com/answers/topic/hardware/question/whats-difference-between-layer-3-switch-and-router

thanks

John Peterson Fri, 09/28/2012 - 01:36
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The devices are going to be edge devices running eigrp to our other sites which have private links.


Would a 3560 allow us to switch at 100mb?


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John Peterson Fri, 09/28/2012 - 01:43
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Thanks


There if I was to use a L3 switch which had a through of 32gi it would allow routing speeds of such speed, I only need routing speed of 100mb?


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singhaam007 Fri, 09/28/2012 - 01:59
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But you can change the speed, like we do one most of our switches. We always change our one connection to 100MB

Please check this link

http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_52_se/configuration/guide/swint.html#wp1080632

and see this section

Configuring Interface Speed and Duplex Mode

thanks

      

singhaam007 Fri, 09/28/2012 - 02:00
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sorry it was " we always change our one office connection"

xcz504d1114 Fri, 09/28/2012 - 07:37
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You're not going to come anywhere near the capabilities of a 3560 with 50'ish users, the Layer 3 switch will work fine, and also your router on a stick scenario will also work fine for what you have described so far.


From a simplicity perspective, the layer 3 switch is a better idea. From a throughput perspective, the layer 3 switch is most likely a better idea as well, a router on a stick design reduces the throughput of an interface by half.


For a high end environment with heavy route processing, a layer 3 switch is typically not recommended, because it does routing in software, where as a router uses hardware, but you have not described an envrinoment that will be demanding on layer 3 performance.


HTH,

Craig

Jon Marshall Fri, 09/28/2012 - 07:44
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Craig


For a high end environment with heavy route processing, a layer 3 switch is typically not recommended, because it does routing in software, where as a router uses hardware

You have this wrong way round. Although some high end routers route in hardware most routers forward packets via software. All L3 switches by contrast uses hardware to forward L3 packets and are therefore far more suited to enviroments where you need a high throughput of L3 packets.


Jon

Joseph W. Doherty Fri, 09/28/2012 - 06:05
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A low end L3 switch may provide 100x the performance of a low end router, for about the same price.


Cisco recommends a 3925 for WAN connections up to 100 Mbps (effectively the aggregate performance for all traffic transiting the router).

Jon Marshall Fri, 09/28/2012 - 07:40
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John


As others have said a L3 switch would be better but you would still probably need a router as well to connect to the rest of your sites. You need to work out how much bandwidth you need between sites to scale the router. If you also want to use the same router to route for the vlans then see Joseph's mail. Bear in mid just because a router has 1Gbps interfaces it doesn't meant it support 1Gbps throughput.


One thing to mention is that if you decide to go with the router only option if you find the bandwidth is not enough for your internal vlans then it would be relatively easy to simly purchase a L3 switch at a later date and migrate the vlans to the L3 switch.


Jon

stevewinwood Fri, 09/28/2012 - 13:28
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I agree that router on a stick is fine for this scenario, using something like a 29xx ISR 2 router which like a L3 switch uses CEF to route in hardware when possible. Of course it depends on what the users are doing, but as long as they aren't doing stuff like all streaming HD video it should be fine.

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