broadcasts and networking 2

[just1moretime]

I am trying to understand broadcasting.
With a layer 2 switch,set to default--like a hub. With subnet 1.1.1.X /24 connected to ports 1-12.
With subnet 2.2.2.x /24 connected to ports 13-24. I have an understanding that ip will not allow either
of the subnet's connections to connect. 1.1.1.x will only connect to 1.1.1.x and 2.2.2.x will only
connect to 2.2.2.x. Is this accurate? This thinking makes me think I can use a switch with multiple
subnets connected to it and no need for vlans to have been configured.
Will a broadcast connect between the 2 subnets, what I mean,will a broadcast from 1.1.1.x end up on the
2.2.2.x subnet?
I get the idea that broadcasts get treated 3 ways, basic ip, switch treatment, and router treatment. Any
explanation is appreciated. Thank you.

 

[unclerico]

1.1.1.x will only connect to 1.1.1.x and 2.2.2.x will only
connect to 2.2.2.x. Is this accurate?

Correct

This thinking makes me think I can use a switch with multiple subnets connected to it and no need for vlans to have been configured.

No no, tsk tsk...Bad practice.

will a broadcast from 1.1.1.x end up on the 2.2.2.x subnet?

Yes assuming like you said the config is vanilla

Your question is actually a real scenario that I just dealt with at one of my plants. The original design was enough to make me cry because it was sooooo terrible. We had a 192.168.1.x/24 subnet and a 192.168.2.x/24 subnet all configured in a single broadcast domain, no VLAN's, no L3 devices. The amount of broadcast/multicast traffic sent and received on each "segment" was unreal and it got to the point where it was becoming a performance problem. From day one I have been pleading with the powers that be to let me redesign this network (it's a 24x7x365 plant so we get like 3 days per year where we can actually make changes) and finally I got the call a few weeks ago. It took two days, each about 18 hours long, but it's done and it is freaking flying babay!!!! It was a blast to do because as with most all of you I absolutely love networking and making things right ;-) . What I can never understand is how can people actually get paid to do what the predecessors did in terms of their network design?? All I have to say is WOW!!!! It's always the other guy's fault lol...

Now back to your regularly scheduled programming...

I hate all Uppercase... I don't want my groups to seem angry at me all the time! =)
- ColdFlame (vbscript forum)

 

[lerdalt]

If I'm following you correctly, with the switch setup like a hub (i.e. all ports in the same vlan straight out of the box), then I believe that broadcasts from a 1.1.1.x address will be seen by a 2.2.2.x device, but the 2.2.2.x device will not do anything with it. The broadcast will be sent out over all ports that are configured for the same vlan. If you are familiar with wireshark you could test this quickly.

You are correct that only 1.1.1.x devices will speak to 1.1.1.x and 2.2.2.x will only speak to 2.2.2.x.

I would still setup separate vlans for each subnet, if possible. Just as a good practice.

But I might need more coffee this morning to really be following you and give a better explanation.

 

[burtsbees]

You guys posted at the same time, pretty much with the same answer...lol

Burt

 

[maczen]

Great minds think alike!

Unless discussing OSI concepts! LoL

B Haines
CCNA R&S, ETA FOI

 

[burtsbees]

You think THAT's funny---look at what OSI stands for...and I'M dyslexic...lol

Burt