At 01:03 PM 7/24/01, Peter Van Oene wrote:
>I beg to differ slightly on the concept of VLANS. A VLAN, as I'm sure you
>know, is a broadcast domain and makes no assumption of nor has any
>dependance upon layer three protocols.
I agree in theory. But in practice a VLAN is an IP subnet (on IP networks)
and it helps to think of it this way when designing and troubleshooting. I
get this from Dan Farkas, CCIE and CCSI, author of switching papers at
Certificaton Zone. http://www.certificationzone.com. (No, this is not
another ad for that great service. ;-) But Dan says that he encourages his
students to use the terms broadcast domain, subnet, and VLAN
interchangeably. It helps them understand traffic flow, etc. I think it
might help the poster....
Priscilla
>However, the difference in answers
>between how to extend a protocol independent broadcast domain vs an IP
>broadcast domain over an IP network are subtle and likely moot in this case.
>
>The design choices that could enable this technically challenged network
>would include, as you point out, subneting the IP network such that the
>single subnet becomes two and enabling routing over the IP intermediary
>network, or, bridging the subnet across the IP network using a tunneling
>technique in which case the intermediary network becomes transparent to the
>subnet. The first case is likely the most plausible, though the original
>poster has not indicated that it is indeed IP that needs the services of
>this bridged network.
>
>I think the original poster needs to ask him or her self Howard's cardinal
>question "What problem am I trying to solve?" likely yielding a need to
>redesign toward a more simple, and functional design as you suggest :)
>
>Pete
>
>
>*********** REPLY SEPARATOR ***********
>
>On 7/24/2001 at 12:05 PM Priscilla Oppenheimer wrote:
>
> >Why does the network on the other side of the routers need to be in the
> >same VLAN? Why don't you make it a different VLAN and a different IP
> >subnet?
> >
> >A VLAN is an IP subnet. Sure, Cisco and other vendors make it sound like
> >VLANs are something more mysterious, but essentially, a VLAN is an IP
> >subnet.
> >
> >So you need routing on those routers.
> >
> >But what you have described is a discontiguous subnet. This is usually not
> >a good idea but it could work if you use static routes or a classless
> >routing protocol and tinker with the prefix boundary.
> >
> >But, it's probably a better idea to use a different design where the
> >subnet
> >is not separated by multiple routers. A subnet (VLAN) separated by
> >switches
> >is OK, but a subnet separated by routers is usually avoided. You could use
> >bridging on the routers, but seems like even more of a kludge.
> >
> >If I'm missing something, please let me know. Thanks.
> >
> >Priscilla
> >
> >At 03:35 AM 7/24/01, SolutionFinder SolutionFinder wrote:
> >>Hello colleagues, I have a question regarding the configuration of the
> >>routing device when a VLAN is separated by two or more routers. Do I have
> >>to add an interface for the respective VLAN on every router ? Vlan 20
> >>--> Router A --> Router B --> Router C --> Vlan 20 Do all three routers
> >>need the 'interface VLAN 20' statement in their configurations ? Thanks
> >>for your help in advance. Regards, Hans
> >>
> >>------------------------------------------------------------------------
> >>
> >>Get your FREE download of MSN Explorer at http://explorer.msn.com
> >________________________
> >
> >Priscilla Oppenheimer
> >http://www.priscilla.com
________________________
Priscilla Oppenheimer
http://www.priscilla.com
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