SVI vs Routed port

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Aug 15th, 2007
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Hi all

If i have Layer3 devices connected between them. I want to routing and speaking with ip address so i have 2 choices between i create svi and setup configure as routed port (no switchport). How could i choose between them to the most efficiency

thanks

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ankbhasi Wed, 08/15/2007 - 21:17
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Hi Friend,


There is a difference the way both the connection works. Although they will have the same purpose but there is the difference the way the switch ports will work.


In case of a SVI you will have eventually a Layer-2 link between the switches. This will run your normal STP and other control traffic between the switches.This will extend your STP domain from a switch to the other switch.The ports will go thorugh the normal STP states and in case of a link flap or link going dowm/coming back the recovery time will be a little high.


In case of a routed port between the switches,you will have a layer 3 link between the switches and will work as a normal router port. There will no STP running on the ports and the STP domain will not be extended beyond the downstream switches.Applring layer3 features like ACL's,PBR's will be a ltille easy in this case.


The Disadvantage of running routed ports is that each port will be a separate network and you will have to manage a large number of IP subnets on the network. Running a routing protocol will be a good idea in this case.


HTH


Ankur


*Pls rate all helpfull post


tomek0001 Mon, 06/16/2008 - 16:43
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Hello,

In term of performance would you say one is better than other?


Also what is the problem with SVI and ACLs and PBR?


thank you.

foxbatreco Mon, 06/16/2008 - 19:17
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Normal L2 switches have Vlan1 by default..this is sort of SVI.

SVI allow you to do intervlan routing w/o involving a router.Also another notable point is the hardware for the SVI interface u create is an EtherSVI .

Choice of SVI's or routed ports depends on wat devices are on the other end of the connection.


This can be explained by 2 scenario's.We have 2 hosts on different vlans trying to communicate with an L3 MLS in between.

*first is using SVI::The L3 will allow Intervlan routing w/o a router.We create 2 SVI's with int vlan XX command alongwith the ip assigned on it.

We'll have to enable ip routing on an L3 switch as its off by default.With this hosts should ip of the respective vlan SVI's as their gateway and they will communicate.

*Ports on a MLS will run as L2 by default.To change this to routed port..use no switchport alongwith the ip address on the interface.Then enable routing using some dynamic protocol and its done.

Sankarganesh Ba... Fri, 06/21/2013 - 00:14
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Hi ,


I want to know in a situation like if a router and switch is connected with Routed port.


why we use routed port in this scenario?????? what will be the application.


can anyone please brief me about this... thanks in advance

Peter Paluch Fri, 06/21/2013 - 02:20
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Hello,


why we use routed port in this scenario?????? what will be the application.


A routed port on a switch has almost all Layer2 management protocols stopped and deactivated so it is an ideal boundary between different Layer2 domains.


When talking about how to design and use VLANs, it has become the best practice to not allow VLANs used on access and distribution switches to "leak" into the core layer. One of the easiest ways to accomplish this is to simply connect a switch and a router using a routed port on the switch. As this port is outside of any manually defined VLAN on the switch, it easily prevents these VLANs including protocols such as DTP, VTP, STP to try to "interact" with the connected device.


My two cents.


Best regards,

Peter

Rolf Fischer Fri, 06/21/2013 - 02:30
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Hi,


I'd like to point out a convergence issue in addition to Peter's posting:


A router normally doesn't run STP. So even with RSTP, the router won't answer the switch's proposal BPDU.

As a result, after a link change it takes 2x forward delay until a Layer-2 switchport changes into forwarding state (30 sec).

A routed port in contrast will be active almost immediately.

Of course, in a loop-free topology you can "speed up" the swichport with "portfast" which should be combined with "bpdu guard".


Another possible issue when using a routing protocol can be the different link-down behavior of a SVI:

https://supportforums.cisco.com/message/3547727

For an optimization you'll need additional configruation again.



Hope that helps

Rolf

Joseph W. Doherty Fri, 06/21/2013 - 02:57
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Disclaimer


The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.


Liability Disclaimer


In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.


Posting


In theory, by default configuration, the routed port would be a little more efficient for a p2p link as all the unnecessary L2 packets (as described by Peter) would be automatically deactivated.  Also for a p2p configuration, the routed port would be "cleaner".


BTW, from other posting on this site, mention was made that (some) switch routed ports are still SVIs, but "hidden" by the IOS.  Such a "hidden" SVI looks different in the configuration and has unnecessary L2 features automatically deactivated.

sugatada9 Sat, 06/22/2013 - 09:48
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What is the difference in command to configure a routed port? i think no switchport & assign ip is enough for routed port? then where is the difference? how switch recognise a routed port?

Joseph W. Doherty Sat, 06/22/2013 - 11:16
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Disclaimer


The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.


Liability Disclaimer


In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.


Posting


Yes, often all you need to do a Catalyst switch that supports routed ports is use the "no switchport" command.  (BTW: I recall default differs across different Catalyst switches.  For example, 3750s default to switchports, and I believes 6500s default to routed ports.)


Also yes, you would than assign a routed port an IP address.


How the switch recognizes the status of the port is how the port is configured, either explicitly or by default.


What's the differerence?  As noted in other posts, routed port configuration is a bit different and it automatically suppresses some L2 traffic.

zekebashi Thu, 11/13/2014 - 13:04
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Hello, 

I created a routed interface on one access switch and assigned it an IP address: 10.34.34.252/24). I uplinked this port(Gi0/48) to a port (member of VLAN525)  in another access switch which has an SVI(IP Address 10.34.34.253/24). My question is will a routed interface be able to communicate with the SVI( Interface VLAN525; IP address 10.34.34.253/24)? I hope I didn't confuse you!! 

Thx in advance. 

Best, ~zK 

 

sameer kumar chug Fri, 11/28/2014 - 03:42
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Yes, the routed interface will work with SVI perfectly. However you would see some "unknown protocol drops" on routed interface side because of L2 protocols of other end.

 

Regards

Sameer

zekebashi Wed, 12/03/2014 - 12:12
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Thank you, Sammer!

I was able to create a routed port and also configure an SVI port and both were able to communicate just fine. 

Thanks for your input. 

Best, ~zK 

bcoverstone Mon, 05/25/2015 - 18:14
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Remember, all routed ports ultimately perform their physical communication via layer 2.  So even though a routed interface is "Layer 3" it ultimately performs an ARP and talks to the other side via the MAC address.

 

Given that, a routed port with an IP address (no switchport) is the same as a switched port with a VLAN assigned to only that physical port (so it can't be looped), with STP filtering on, BPDU guard off, DTP off, VTP off, and an IP address assigned to the SVI.  The routed port just packages that all into one easy statement.

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