Broadcast clarification

[RookThis]

I have a subnet with a 22 bit mask which is almost maxed out. We have some users on that subnet that run an application that accesses an oracle server, which fails intermittenly. We moved one of the users over to a new subnet and never fails. We are thinking that /22 subnet is over subscribed and is impacting network performance. We are seeing a lot of broadcast traffic, and have found some printers on that subnet with the wrong masks. Could someone tell me what impact no ip direct broadcasts would have on the router's interface for this subnet. I think it means that the router will prevent broadcasts ourside of the local subnet? I think I'm wrong, but need someone to clarify this for me please. Thanks for any assistance that anyone can provide.

 

[wybnormal]

No ip direct broadcasts will break things like DHCP crossing the router. I found this one out the hardway after an upgrade from an older IOS to a newer one where this is the default

You need to chase down what is sending all the broadcasts.. also check to make sure that the devices are configured for IP only if that is all you are using. MS will send broadcasts in ALL protocols enabled.. so if you have IP, IPX and Netbuei enabled, you get 3 broadcasts for the price of one. And even if the client is IP only, an IPX broadcast will be picked up and partially processed since layer 2 is layer 2. I just did a off-protocol attack in the lab using IPX against an IP network and brought it to it's knees even though the clients were IP only. It was *enlighting* to say the least.

MikeS
Find me at

http://www.packetattack.com

"Take advantage of the enemy's unreadiness, make your way by unexpected routes, and attack unguarded spots."
Sun Tzu

 

[routerman]

I'd agree with MikeS, you describe a problem of intermittant connection failure. I've looked at many similar network problems on many customer sites and found excessive broadcast traffic causes all sorts of odd problems. If you have access to an analyser, set it to capture only broadcast traffic or stick it into a switch port, have a look at what protocols are appearing.

Also I would recommend setting the command NO IP DIRECTED-BROADCAST, if you run into DHCP related problems use the IP HELPER command instead.

 

[CCIEWANNABE]

Place the most frequently used protocol first to speed up network access. Fewer protocols generate less network traffic. Newer drivers can enhance performance. Download the newest driver from your manufacturer. Unbind unneeded protocols to reduced network traffic. Reducing the idle disconnect timeout. This will reduce browser traffic from PC's. Excluded heavily used servers from being the Domain Master Browser. Force name resolution to be resolved locally. A really big tip is to disable all of the protocols and frame types not used on the network for printing on the printers. Printer’s broadcasts allot because most admin don’t check the Network protocols installed by default with the printer software. In your posting do thee items then run a baseline test. Move up the Layers. Sometimes it’s a mis-configured spanning tree protocol. Route once; switch many

 

[RookThis]

How would you determine a misconfigured spanning tree protocol?