VLANs, routing, multicast and HP switches, oh my...

[Kurt Buff]

On Thu, Jun 10, 2010 at 07:02, Ivan Voras <ivoras at freebsd.org> wrote:
> On 06/09/10 22:35, Kurt Buff wrote:
>> All,
<snip>
>> Now, however, the subnet on fxp4 is going to have an HP 2610 switch
>> attached to it, and they want to hang multiple subnets from that
>> interface.
>
> ... which doesn't necessarily translate to VLANs. You can assign an
> arbitrary number IP addresses to a single NIC without problems.

True - but they are apparently going to be simulating hundreds of
machines on two subnets, as I found out a day later. Sorry for the
late reply - been slammed at work.

>> So, it looks to me as if I need to set up this box with a VLAN
>> configuration and some more routing intelligence than it has at the
>> moment.
>>
>> I'm looking at, among other pages, this one
>> http://www.cyberciti.biz/faq/howto-configure-freebsd-vlans-with-ifconfig-command/,
>> though I don't see much addressing these two subjects in the handbook.
>
> There's not much to say on the topic. The section which describes VLAN
> setup in the link you have given is correct. Each new virtual vlan
> device will behave as another NIC.

Good to know. Thanks for that.

> The story behind VLANs is that they are an Ethernet-level routing
> kludge. Instead of having a flat topology, they divide it into chunks
> which may be routed separately on L2.

Yep - do that with my HP switches in the rest of the environment.

> On the FreeBSD side, the
> representation of this will be additional NICs which operate only on
> these "chunks" - virtual Ethernets which don't see packets from other
> VLANs even if they travel on the same wire(s). The physical NIC will
> need to "see" all packets indiscriminately (which is sometimes called a
> "trunk"), and the OS logic will then "divide" those packets into
> individual virtual vlan devices. Note that if you use VLANs, all active
> equipment involved will probably need to be able to understand and work
> with VLANs, and you will need to configure them all. To be able to use
> generic Ethernet clients (like Windows with low-end NICs), some kind of
> end-point equipment will need to strip VLAN tags before the packets
> reach them.
>
> But as I've said, maybe you don't need VLANs. Simply hang multiple IP
> subnets on normal Ethernet NICs.

Again - they'll be putting up to 200 busy machines on each subnet. It
seems reasonable to limit the broadcast domains with VLANs.

Thanks for the feedback.

Kurt