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Managed Switch: help me understand

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Anonymous
October 11, 2004 5:55:08 PM

Archived from groups: comp.dcom.lans.ethernet,microsoft.public.win2000.networking (More info?)

Hi,

To effectively use the Network Load Balancing (NLB) capability that is
built into Windows, it's important that the servers sharing the common
virtual IP address be plugged into a hub, not a switch. The reason for this
is that these servers share a common virtual MAC address. A switch would get
confused when it tries to "learn" the appropriate port for the virtual MAC
address. This is why a whitepaper that I recently read recommends:

- plugging the servers in the cluster into a hub
- uplinking that hub into a switch

This ensures that each server in the cluster is able to see each packet
destined for the virtual MAC address. This is all pretty standard stuff, but
here's the thing: I don't want to have to mount a separate hub in my rack
for each cluster. Can I accomplish the same thing with a "managed switch"?
I've never used a managed switch before, so I'm not sure.

Let's say I have a managed switch with 24 ports. I fill up ports 1-16
with Ethernet cables from various machines on my LAN... but I then plug in
the two servers in my cluster into ports 23-24. I want ports 23-24 to act
like a hub that is unlinked to the rest of the switch. Eventually, the
switch would learn that the shared MAC address of the cluster lives behind
ports 23-24 and all traffic destined for that MAC address would be
*broadcast* to those two ports. Does that make sense?

I'm not sure what the appropriate jargon/terminology is for this type of
setup, but I've done some research and I think it's called a VLAN. The
crucial point to note here, though, is that ports 23-24 would act as a hub
(all traffic is broadcast) instead of a switch.

All comments are appreciated.

Thanks...
Anonymous
October 11, 2004 6:02:12 PM

Archived from groups: comp.dcom.lans.ethernet,microsoft.public.win2000.networking (More info?)

On Mon, 11 Oct 2004 14:55:08 -0700, Sal Bompensaro wrote:

> I'm not sure what the appropriate jargon/terminology is for this type of
> setup, but I've done some research and I think it's called a VLAN. The
> crucial point to note here, though, is that ports 23-24 would act as a hub
> (all traffic is broadcast) instead of a switch.

Many switches also allow you to put specific ports in "monitor mode" -
where the ports you specify will get all traffic that the switch sees.

-Kam
Anonymous
October 11, 2004 6:19:47 PM

Archived from groups: comp.dcom.lans.ethernet,microsoft.public.win2000.networking (More info?)

> Many switches also allow you to put specific ports in "monitor mode" -
> where the ports you specify will get all traffic that the switch sees.

Cool, I guess that's what I'm looking for, as long as I can make the
"monitor mode" only apply to the ports in my VLAN instead of the whole
switch.
Related resources
Anonymous
October 12, 2004 11:15:12 AM

Archived from groups: comp.dcom.lans.ethernet,microsoft.public.win2000.networking (More info?)

In article <wLydnZKAo4ewbvfcRVn-qA@giganews.com> "Sal Bompensaro" <jackson@sanford.son> writes:
>From: "Sal Bompensaro" <jackson@sanford.son>
>Subject: Managed Switch: help me understand
>Date: Mon, 11 Oct 2004 13:55:08 -0700

> I'm not sure what the appropriate jargon/terminology is for this type of
>setup, but I've done some research and I think it's called a VLAN. The
>crucial point to note here, though, is that ports 23-24 would act as a hub
>(all traffic is broadcast) instead of a switch.

I think You have to use PORT TRUNKING for this purpose, not VLAN.


--
Pozdrowienia!!StaCH
mailto:schmielarz@stanislaw.chmielarz.name
http://www.uniprojekt.com
Przy odpowiadaniu na priv'a wytnij duze litery.
Anonymous
October 12, 2004 5:04:39 PM

Archived from groups: comp.dcom.lans.ethernet,microsoft.public.win2000.networking (More info?)

Naw,..Port Trunking is a VLAN thing where the router uses the same physical
interface (with same cable and switch port) to serve multiple VLANs. The
line between it and the switch becomes the Trunk Line. Investigate the term
"Router on a stick" for more details.

For load balancing, the right way, requires a switch that is specifically
designed for load balancing multiple NICs.

--

Phillip Windell [MCP, MVP, CCNA]
www.wandtv.com


"Stanislaw Chmielarz" <schmielarz@uniprojekt.com.PL> wrote in message
news:schmielarz.4509.0@uniprojekt.com.PL...
> In article <wLydnZKAo4ewbvfcRVn-qA@giganews.com> "Sal Bompensaro"
<jackson@sanford.son> writes:
> >From: "Sal Bompensaro" <jackson@sanford.son>
> >Subject: Managed Switch: help me understand
> >Date: Mon, 11 Oct 2004 13:55:08 -0700
>
> > I'm not sure what the appropriate jargon/terminology is for this type
of
> >setup, but I've done some research and I think it's called a VLAN. The
> >crucial point to note here, though, is that ports 23-24 would act as a
hub
> >(all traffic is broadcast) instead of a switch.
>
> I think You have to use PORT TRUNKING for this purpose, not VLAN.
>
>
> --
> Pozdrowienia!!StaCH
> mailto:schmielarz@stanislaw.chmielarz.name
> http://www.uniprojekt.com
> Przy odpowiadaniu na priv'a wytnij duze litery.
October 15, 2004 1:27:59 AM

Archived from groups: comp.dcom.lans.ethernet,microsoft.public.win2000.networking (More info?)

"Sal Bompensaro" <jackson@sanford.son> wrote in message
news:wLydnZKAo4ewbvfcRVn-qA@giganews.com...
> Hi,
>
> To effectively use the Network Load Balancing (NLB) capability that is
> built into Windows, it's important that the servers sharing the common
> virtual IP address be plugged into a hub, not a switch. The reason for
this
> is that these servers share a common virtual MAC address. A switch would
get
> confused when it tries to "learn" the appropriate port for the virtual MAC
> address. This is why a whitepaper that I recently read recommends:
>
> - plugging the servers in the cluster into a hub
> - uplinking that hub into a switch

A URL to the paper would help someone help you....

But what you really need is for the switch to deliver a copy of each inbound
packet to the NIC cards at each server.

depending on how you configure the cluster, this is either a conventional
unicast MAC address, or a multicast address. Multicast will work with a
switch, but has its own issues,

a hub does this in the hardware, but since hubs top out at 100 Mbps, with
modern servers and Gigabit capable interfaces, the hub may limit overall
throughput.

>
> This ensures that each server in the cluster is able to see each
packet
> destined for the virtual MAC address. This is all pretty standard stuff,
but
> here's the thing: I don't want to have to mount a separate hub in my rack
> for each cluster. Can I accomplish the same thing with a "managed switch"?
> I've never used a managed switch before, so I'm not sure.

You need a switch that can handle your cluster setup(s), and you may need
each cluster in its own subnet.
>
> Let's say I have a managed switch with 24 ports. I fill up ports 1-16
> with Ethernet cables from various machines on my LAN... but I then plug in
> the two servers in my cluster into ports 23-24. I want ports 23-24 to act
> like a hub that is unlinked to the rest of the switch. Eventually, the
> switch would learn that the shared MAC address of the cluster lives behind
> ports 23-24 and all traffic destined for that MAC address would be
> *broadcast* to those two ports. Does that make sense?
>
> I'm not sure what the appropriate jargon/terminology is for this type
of
> setup, but I've done some research and I think it's called a VLAN. The
> crucial point to note here, though, is that ports 23-24 would act as a hub
> (all traffic is broadcast) instead of a switch.

Yes it does do some of what you want - but no setting up a VLAN does not
make the switch behave as a hub - it makes it behave as a collection of
separate switches.

You would isolate the cluster within a VLAN, sort out a way to send cluster
traffic to all attached ports, but then you add a router (or the routing
inside your layer 3 switch) to connect that VLAN as a separate subnet to the
rest of your network.

If you use unicast cluster MAC addresses, then you have to configure the
switch to replicate traffic to that MAC address to each relevant port. If
you use this setup, then you dont have to isolate clusters on their own
subnets / vlans, but it is going to make it easier to fault find, configure
and change later if you do.

If you use multicast cluster MAC Addresses, then you need a router (or layer
3 capable switch) willing to ARP and work with a multicast MAC address, or
that allows you to set that mapping manually.

Either way you need switch(es) with high end capabilities that allow for the
setup you choose. i suggest you get your vendor to spec them for this
purpose and agree and actually do a functional test for the load balancing
working correctly before you pay for any hardware.
>
> All comments are appreciated.
>
> Thanks...
--
Regards

Stephen Hope - return address needs fewer xxs
!