Calculation of broadcast rate

[ruster]

Hello again,

I am trying to determine the best method of calculating the percentage of broadcast traffic on a given network. Originally, I thought that I can perform a "sh interface" command on a given interface, extract the number of input packets and broadcasts, and use those values to derive a percentage. However, after further investigation, I found out that those values reflect packets which are process switched on the router. Therefore any packets using any other switching mechanism (fast, cef, etc), are not reflected in those values. I assume that I will have to extract information from several commands now to attain the data I need. Just curious how the tek-tip community has been handling this task?

Any suggestions would be appreciated.

Ruster.

 

[gconnect]

cisco-specific: since broadcast normally stay local to the LAN why don't you just turn fast switching off

int eth0
no ip route-cache
no ip mroute-cache

__________________________________________________________

OK
really, unless your router is attached to a hub you will not have an accurate depiction of the amount of broadcasts because your router will not see all LAN traffic (i.e. 10.1.1.3 connecting to 10.1.1.4). after the switch or hub gets the arp request and floods it out all other ports (including the routers link) and the VC is built, the lan devices will talk directly until that CAM entry in the switch times out. Therefore you will miss a substantial amount of traffic souly depending on the router alone.

if you have a hub or a switch with a SPAN port, you can throw a windows or linux box on it and run a packet sniffer like Ethereal that will give you a breakdown of all traffic. remember when trying to weed out true broadcast traffic, the ARP requests are always needed, everything else should be investigated. even the arps can be cut down if you have a pure switched environment (no hubs).