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BVI - What is it and what are its uses?

BVI - What is that and what are its uses?

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VIP Mentor

BVI - What is it and what are its uses?

Best BVI-explaination I've ever read!

-- 
Don't stop after you've improved your network! Improve the world by lending money to the working poor:
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9 REPLIES 9
Hall of Fame Cisco Employee

Re: BVI - What is it and what are its uses?

Ranji,

A BVI is in fact quite similar to an SVI (interface Vlan). You can define a software bridging between various ports of a router, similar to switching between various ports on a switch. If the ports on a switch belong to the same VLAN and the switch is capable of multilayer switching, you can create an interface Vlan for that VLAN and allow the hosts in that VLAN to use the IP address of the interface Vlan as their default gateway.

The same goes for interface BVI - Bridged Virtual Interface. When configuring software bridging, you define a group of interfaces that are bridged - the router performs bridging (i.e. software-based switching) of frames between all member ports of a bridge group, in essence forming a single broadcast domain - an IP subnet. If the devices in the common bridge group want to access other IP networks, they need a gateway, so you create an associated interface BVI that is also a part of the bridge group, and devices in the bridge group then use the IP address of the BVI interface as their gateway.

For exampe, imagine a router with two FastEthernet interfaces:

bridge irb

!

interface FastEthernet0/0

no ip address

no shutdown

bridge-group 1

!

interface FastEthernet0/1

no ip address

no shutdown

bridge-group 1

!

interface BVI1

ip address 10.0.0.1 255.255.255.0

no shutdown

!

bridge 1 route ip

This configuration would make your router to basically behave as a 2-port "switch" on its Fa0/0 and Fa0/1 interfaces, and devices connected to these ports would use the 10.0.0.1 as their default gateway to other networks.

You rarely configure bridging exactly this way these days, as switches are orders of magnitude faster and have way more ports. Still, there are situations where you need to bridge two interfaces, taking packets out of frames of one technology and putting them into frames of a different technology, without routing them, just repackaging but still carrying them between interfaces. This is often done in, say, DSL if the router is configured to act in bridge mode - take IP packets coming to Ethernet interface and simply repackage them into PPP or ATM+AAL5 cells on the DSL WAN port (and vice versa).

Best regards,

Peter

VIP Mentor

BVI - What is it and what are its uses?

Best BVI-explaination I've ever read!

-- 
Don't stop after you've improved your network! Improve the world by lending money to the working poor:
http://www.kiva.org/invitedby/karsteni

View solution in original post

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Beginner

Re: BVI - What is it and what are its uses?

Neat, thanks!

Beginner

Re: BVI - What is it and what are its uses?

Thanks for the explanation

VIP Advisor

Re: BVI - What is it and what are its uses?

Hello
An BVI used in bridging
Please review the below link it will explain nicely how a bridging works

http://www.cisco.com/en/US/tech/tk389/tk815/technologies_tech_note09186a0080094663.shtml

Res
Paul


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kind regards
Paul

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Hall of Fame Community Legend

Re: BVI - What is it and what are its uses?

The most common use of Bridged Virtual Interface is when you configure wireless access points (APs).

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Hall of Fame Cisco Employee

Re: BVI - What is it and what are its uses?

Hi Leo,

I agree - but it should be said that on APs, the BVIs are used just for management and control plane traffic, and they do not provide the gateway function for which they have originally been invented when IRB became supported on routers. In other words, BVIs on autonomous APs are there to assign IP addresses to APs so they can be remotely managed, talk to RADIUS/TACACS servers etc., but not for routing purposes.

Best regards,

Peter

Hall of Fame Community Legend

Re: BVI - What is it and what are its uses?

Hi Peter,

That's correct. However, I've never encountered BVI until I started playing with APs. And this is the point I'm trying to imply.

PS: Happy New Year to all! :)

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Hall of Fame Cisco Employee

Re: BVI - What is it and what are its uses?

Hi Leo,

Yes - of course. I did not mean to belittle your answer and experiences - I am sorry and I apologize if it sounded that way.

Happy New Year to you, too! Although here in Slovakia, we still have 2013 as of writing this response. Yeah, we're quite behind

Best regards,

Peter

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