×

Warning message

  • Cisco Support Forums is in Read Only mode while the site is being migrated.
  • Cisco Support Forums is in Read Only mode while the site is being migrated.

BVI - What is it and what are its uses?

Endorsed Question
Dec 31st, 2013
User Badges:

BVI - What is that and what are its uses?

Cisco Endorsed by rajavier
Karsten Iwen about 3 years 7 months ago

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

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 5 (4 ratings)
Loading.
Peter Paluch Tue, 12/31/2013 - 01:27
User Badges:
  • Cisco Employee,

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

Karsten Iwen Tue, 12/31/2013 - 04:32
User Badges:
  • Purple, 4500 points or more
  • Cisco Designated VIP,

    2017 Firewalling, VPN

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

Leo Laohoo Tue, 12/31/2013 - 04:23
User Badges:
  • Super Gold, 25000 points or more
  • Hall of Fame,

    The Hall of Fame designation is a lifetime achievement award based on significant overall achievements in the community. 

  • Cisco Designated VIP,

    2017 LAN, Wireless

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

Sent from Cisco Technical Support Nintendo App

Peter Paluch Tue, 12/31/2013 - 04:30
User Badges:
  • Cisco Employee,

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

Leo Laohoo Tue, 12/31/2013 - 05:48
User Badges:
  • Super Gold, 25000 points or more
  • Hall of Fame,

    The Hall of Fame designation is a lifetime achievement award based on significant overall achievements in the community. 

  • Cisco Designated VIP,

    2017 LAN, Wireless

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! :)

Sent from Cisco Technical Support Nintendo App

Peter Paluch Tue, 12/31/2013 - 09:15
User Badges:
  • Cisco Employee,

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

Actions

This Discussion