[c-nsp] Catalyst 6500 series switches and Cisco 7600 series routers do not support Integrated routing and bridging (IRB)

[Andre Beck]

Hi,

On Mon, May 16, 2005 at 05:28:15PM +0200, Manu Chao wrote:
> 
> I need to use IRB with bridge protocol IEEE on a 6500 running IOS
> Version 12.2(18)SXD2 but this feature doesn't exist anymore. I
> understand why but I need it ;-)

Do you really *need* to? What are you actually trying to achieve?
 
> I need to bridge n L2 VLANs ending on the 6500 to one L3 VLAN local to
> this same 6500.

There is no such thing as a "L3 VLAN", at least not in orderly designed
networks (some hardware implements the notion of protocol based VLANs
or even IP address based VLANs, but if you ask me, such dissolution of
layers is nothing but a management nightmare). VLANs are L2, as they
are broadcast domains. You can plug an SVI into a VLAN, but this is
nothing more than a virtual way of plugging a Router interface into
a Switchport, it doesn't make the VLAN L3, it just adds a Routed
interface to it.
 
> It is possible to bridge two L3 VLANs with "bridge protocol 1
> vlan-bridging " but it seems we cannot bridge and route on the same
> VLAN.

It is quite simple to bridge them all together: Turn them into a
single VLAN.
 
> Cisco release notes are clear on this issue:
> 
> "Catalyst 6500 series switches and Cisco 7600 series routers do not
> support Integrated routing and bridging (IRB)"

I perfectly understand why they removed it: bridge-groups plus BVIs
is exactly the same thing as is VLANs plus SVIs. It's just two different
ways to say the same thing. The VLAN way is only much simpler to express
as soon as you get into significant numbers of VLANs. Implementing both
schemes at the same time is leading to confusion only (not to mention
that the whole IRB implementation was confuse from day 1, reading the
docs of that still gives me the creeps, it reads as if the author
never understood what bridging vs. routing and L2 vs. L3 really mean;
no wonder they came up with nonsense commands like "bridge 1 route ip").

> Can someone find a solution (other than downgrading to release 11) or
> a workaround?

The solution is to merge the VLANs into one. A workaround has already
been posted, you could of course shortcut the VLANs using physical
wiring. I just don't see any decent sense in doing so when you could
as well easily use a single VLAN. As you didn't explain what you
actually want to do, I can't see why this would constitute a problem.

-- 
                  The _S_anta _C_laus _O_peration
  or "how to turn a complete illusion into a neverending money source"

-> Andre Beck    +++ ABP-RIPE +++    IBH Prof. Dr. Horn GmbH, Dresden <-