How do VLAN's work and can they be implemented to isolate broadcast traffic

By jonathon.johnson ·
I have a Dell PowerConnect 5448 switch. It has many of the Cisco IOS commands, but not all of them. I'm haveing a terrible issue trying to control the broadcast traffic within the network and the only "feature" it has to help with this is "storm control" but it detects in megabytes/sec rather than packets/sec and only goes as low as 3.5 megabytes/sec. I need a much lower tolerance if possible.

Now my second idea that may actually help figure out Where all the broadcasts are coming from, is to use VLANs. Unfortunately, I'm not a networking person and from what I've read, it's only made me more confused so I figured I'd just ask.

I have a setup where I have 1 main L3 switch that manages all the other rooms. Each room has 1 "home run" back to my switch. Each of those rooms is broken up by dummy switches (4-5 eight-twelve port switches per room). There are 9 rooms like this, each with a home run back to my switch. There are also 3 servers directly connected to my switch that each of the rooms needs access too. There's also 1 interface that goes to another switch on another domain that these rooms need access too. On this interface, only 1 IP on port 443 should be allowed and all other packets dropped.

I can't think of any other info off the top of my head that may be needed. I'd like to isolate each room in it's own VLAN to keep down the broadcasting. None of the individual rooms needs to talk to the other directly, they only need to talk back to the servers and the 1 interface and that's it.

If possible, I'd love to setup an ACL to drop all broadcasts, but I don't even know where to start on that. Since I have no testing enviroment for this, I really can't just "figure it out". Any help would be greatly appreciated and if more info is needed, I'll be on all day lol.

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All Answers

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broadcast storms

by patb071 In reply to How do VLAN's work and ca ...

Broadcast storms are caused by the switches. please see link below. If you stop the broadcast storms you may have issues later on. (someone please correct me if i am wrong)
i am sure there are many tools out there to show you where the storms are being generated.

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loops cause storms and Spanning Tree Protocol

by CG IT In reply to broadcast storms

eliminates loops by disabling the redundant links until needed.

not sure if the switch he's using has STP or the IEEE 802.1d enabled.

If he has a loop that is causing the floodeg redundant links then simply enabling STP should resolve the flood problem.

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I do

by jonathon.johnson In reply to loops cause storms and Sp ...

I have STP turned on, I just don't know much about it either. Like I said, not a networking guy by far. Only know a very little about switching.

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so what really is the problem?

by CG IT In reply to I do

are you having broadcast storms which basically will flood the network and crash it?

or is there a host that is broadcasting continuously that is causing network congestion?

If your refering to using ICMP ping on one Vlan and your tring to ping hosts on another Vlan, that won't work. A router would have to route the ICMP ping across the vlans.

Vlans simply segregate hosts connected to a switch from other hosts connected to the same switch without having to use a router. Hosts in one Vlan can not communicate with other hosts on another Vlan without a router providing routing between them.

Vlans can span switches using trunk lines where hosts in VLan blue on switch one can communicate with hosts in Vlan blue on switch two.

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Yes it would seem

by jonathon.johnson In reply to so what really is the pro ...

From the statistics I've been looking at, yes. There's several thousand broadcasts being sent per second but on the other side, there's only 1 interface actually recieveing them and that's the domain controller. The other interfaces are recieveing some, but in comparision, only about 5% of what's being sent.

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Broadcasts meaning?

by CG IT In reply to Yes it would seem

A domain controller can receive lots of traffic from client computers. Especially if the domain controller has to provide DNS services, DHCP services, routing services and so on. Even the perimeter router with RIPv2 enabled will poll the network on a regular basis [every 30 seconds] so there's always traffic.

Broadcasts are a particular type of traffic

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