CRB is less used today since switches can do the job very well.
IRB is more commonly used. At least some of the IXes is using this....
ISPs connect to IX using ATM VC but not willing to put router there.
As a result, the connection to IX end is an ATM sub-Interface. Since
the IX is doing L2 job to switch Ethernet traffic between ISPs (of
course, doing BGP route exchange), the ATM subinterface should be
bridged to the L2 Ethernet switch to do traffic exchange... and
therefore they deploy IRB.
I don't have bad feeling about IRB (neither good feeling). It should
work. However, I encountered lot of silly troubles on lot of IOS
implementations.... such as:
1. 50% packet discard (not due to the load. It just happened normally)
from FE to ATM BVI. (12.0.7T)
2. After reconfig other ATM VC, the whole PA-A3 is down and require
reload. Even at 12.0.10GD on a 7507.
3. I need to place my PA-A3 to a ealier firmware version in order to
make it work probably.
4. Due to STP, I cannot really do multipath load balancing (old
bridged network problem).
In most case, I think IRB should be avoided. This is my 0.02.
On 29 Apr 2001 23:05:40 -0400, [EMAIL PROTECTED]
("andyh") wrote:
>CRB - route OR bridge on a per-protocol basis
>
>IRB - route and bridge in whatever combination you wish
>
>these technologies are (I would imagine) rarely used these days, anyone use
>much real bridging out there still (aside from SR/TLB maybe)? I would think
>that most bridging is done with switches these days, and the IRB is done
>with ISL-attached routers or L3 cards (RSP/MSM/MSFC)
>
>Andy
>
>----- Original Message -----
>From: "Dennis Laganiere"
>To:
>Sent: Sunday, April 29, 2001 8:17 PM
>Subject: IRB and CRB [7:2476]
>
>
>> I'm trying to make sure I've got these two straight. Here are my notes,
>and
>> I appreciate any feedback on these two bridging techniques:
>>
>>
>> Concurrent Routing and Bridging (CRB)
>>
>> Normally, a networking device either bridges or routes protocols across
>all
>> of its interfaces. With CRB you can bridge protocols on some interfaces
>and
>> route different protocols on other interfaces. You cannot route and
>bridge
>> the same protocol on a router.
>>
>> The major limitation to CRB is that you cannot receive a bridgeable frame
>> and route it, or inversely, receive a routed packet and bridge the frame.
>> The two are separate and cannot be forwarded to each other.
>>
>>
>> Integrated Routing and Bridging (IRB)
>>
>> IRB allows the router to bridge and route the same protocol on a router.
>In
>> order to use IRB you create a Bridged Virtual Interface (BVI). After the
>> BVI is configured, the router can send routable protocols that were
>bridged
>> to the BVI to be routed. For example, an IP packet arrives on a routers
>> interface as a bridged protocol. The destination is out another interface
>> that is not configured for bridging. The router then sends the packet to
>> the appropriate interface to be routed. With IRB you must configure the
>> protocols that you want the BVI to be able to route.
>>
>> IRB can be especially useful as a means of connecting bridged and routed
>> networks during network migrations when the two types of networks must
>> communicate. It provides a border checkpoint for the two networks to pass
>> through.
>> FAQ, list archives, and subscription info:
>http://www.groupstudy.com/list/cisco.html
>> Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
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