Solved

L3 Switches and Router on a stick

Posted on 2014-07-28
10
414 Views
Last Modified: 2014-08-04
If I understand L3 switches when configured with SVIs , improves the performance compared to the old method of using Router On Stick.

in the snapshot below, taken from Cisco website, PCs are connected to L2 Switches, assuming L2 Switches are configured with Separate Vlans, then L2 Switches  are trunked to L3 Switch.
 
In this case if foe instance a PC in Vlan 20 wants to talk to another PC in Vlan 30, the traffic will still have to go through the Trunk Link between L2 and L3 Switches , then it gets routed from Vlan 20 to Vlan 30 in L3 Switch, then will come back through the Trunk to L2 Switch Vlan 20 then to the PC.
I wonder if there is any better performance using L3 switch in this case than using Router on a Stick .

To my understanding, The only case where L3 is better in performance than the router on a stick, is when PCs are directly connected to L3 switch and Vlans are directly configured on that L3 Switch as well as the SVIs with IP Routing command.

I could be wrong, but please shade some light on this.

Thanks
0
Comment
Question by:jskfan
  • 5
  • 5
10 Comments
 
LVL 50

Assisted Solution

by:Don Johnston
Don Johnston earned 500 total points
ID: 40223840
L3 switches are significantly faster routing traffic than a comparable router.  But in your example, the L2 to L3 trunk could still be a point of contention.
0
 

Author Comment

by:jskfan
ID: 40224791
<<But in your example, the L2 to L3 trunk could still be a point of contention. >>>
Which topology do you suggest so that there will not be traffic congestion ?
0
 
LVL 50

Assisted Solution

by:Don Johnston
Don Johnston earned 500 total points
ID: 40224872
You would have to connect the hosts to an L3 switch. But that's isn't necessarily something you would have to do.  It would depend on the traffic flow.
0
 

Author Comment

by:jskfan
ID: 40225542
I believe most of the medium to large environment plugs user PCs to L2 switches and even Trunk L2 switches to other L2 switches, then use L3 switches as backbone switches , that 's where they configure SVIs and routing between Vlans.
I could be wrong that's only my assumption...but if that is the case I do not think PCs get a better response time than if they were directly plugged to L3 Switches and routing is enabled right there on the L3 Switch.

**Second thought, I guess you still can plug PCs to L3 Switches, and configure a domain so that you will have the same Vlans  on other switches , and if one L3 switch does not have enough ports for PCs, other L3 switches still can be used....
example L3 Switch1 can have 30 ports in Vlan20 and 16 ports in Vlan40, and L3 switch2 can have 15 ports in Vlan40 (I said Vlan40 because Switch1 does not have enough ports left for PCs to put in Vlan40)...
But the question that will come up is, whether we can configure Interface Vlan40 on both Switch1 and Switch2 and assign it the same IP address....

Thanks
0
 
LVL 50

Expert Comment

by:Don Johnston
ID: 40226485
I believe most of the medium to large environment plugs user PCs to L2 switches and even Trunk L2 switches to other L2 switches, then use L3 switches as backbone switches , that 's where they configure SVIs and routing between Vlans.
This is correct.
I could be wrong that's only my assumption...but if that is the case I do not think PCs get a better response time than if they were directly plugged to L3 Switches and routing is enabled right there on the L3 Switch.
This is correct also.
But the question that will come up is, whether we can configure Interface Vlan40 on both Switch1 and Switch2 and assign it the same IP address....
No. You can't do that.  This is a situation where a FHRP such as HSRP, VRRP or GLBP would be used.
0
How to improve team productivity

Quip adds documents, spreadsheets, and tasklists to your Slack experience
- Elevate ideas to Quip docs
- Share Quip docs in Slack
- Get notified of changes to your docs
- Available on iOS/Android/Desktop/Web
- Online/Offline

 

Author Comment

by:jskfan
ID: 40227699
if you have no available ports in Switch1 for PCs to put in VLAN40, then you cannot create Vlan40 on Switch2 that has more empty ports ???

I though VTP is to have the same VLANs in multiple switches ?
0
 
LVL 50

Expert Comment

by:Don Johnston
ID: 40227729
if you have no available ports in Switch1 for PCs to put in VLAN40, then you cannot create Vlan40 on Switch2 that has more empty ports ???
I guess that I'm missing something. I don't understand the question.

I though VTP is to have the same VLANs in multiple switches ?
That is correct.
0
 

Author Comment

by:jskfan
ID: 40227770
The question was about using L3 Switches to plug user PCs to.
Then if an L3 Switch has 24 ports, and just Vlan40 by itself has 60 PCs to plug to...
You may need about 3 L3 switches for to get 60 PCs to plug to Vlan40....
0
 
LVL 50

Accepted Solution

by:
Don Johnston earned 500 total points
ID: 40227778
Correct. Or you could use a switch with more ports or you could use L2 switches.
0
 

Author Closing Comment

by:jskfan
ID: 40239425
Thank you
0

Featured Post

Why You Should Analyze Threat Actor TTPs

After years of analyzing threat actor behavior, it’s become clear that at any given time there are specific tactics, techniques, and procedures (TTPs) that are particularly prevalent. By analyzing and understanding these TTPs, you can dramatically enhance your security program.

Join & Write a Comment

It happens many times that access list (ACL) have to be applied to outgoing router interface in order to limit some traffic.This article is about how to test ACL from the router which is not very intuitive for everyone. Below scenario shows simple s…
I have seen some questions on problems with SSH/telnet access to Cisco routers that may occur despite the fact that from a PC connected to your LAN, Internet connectivity is in place and users can access Internet sites without any issues.  There are…
After creating this article (http://www.experts-exchange.com/articles/23699/Setup-Mikrotik-routers-with-OSPF.html), I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…
After creating this article (http://www.experts-exchange.com/articles/23699/Setup-Mikrotik-routers-with-OSPF.html), I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…

760 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

20 Experts available now in Live!

Get 1:1 Help Now