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Help with understanding the concept of interface traffic


I've got cacti running monitoring the switch network interfaces. I'm a little confused with how the graph depicts incoming and outgoing traffic on the interface. Can someone please exaplain what is categorised as incoming on an interface and what is outgoing?

Let's say traffic enters port1 i.e it is sent from a server, I assume that is incoming traffic into port 1, and then its also outgoing from port 1 since it is being sent out to another interface. Now lets say that same traffic is sent to port 4, port 4 will now receive that traffic, isn't this incoming traffic for port 4? and when port4 send it out to the attached server doesn't this also become outgoing traffic?

So my confusion then is that you can't get a true figure on how much traffic is flowing inbound and outbound.

Maybe its a case of taking only one reference point, but I'd appreciate if somone can clear this up.




Re: Help with understanding the concept of interface traffic

Hi Dan,

Assume yourself sitting insite the switch. Not try to analyze what would be the incoming and outgoing traffic.

The traffic that enters the interface from outside the switch would be considered as incoming while the traffic which would leave the interface [from switch to outside] would be considered as outgoing traffic.

Please forgive me since I am not very good in explaining. I am not sure if this is the best example to explain this.

-> Sushil

Hall of Fame Super Gold

Re: Help with understanding the concept of interface traffic


I believe that Sushil has given pretty much the standard explanation that incoming and outgoing are from the perspective of the switch. And it is a pretty good explanation. I would add to his explanation that the traffic inbound on port 1 is sent to outbound port 4 using the switch backplane and the backplane traffic is not part of what is monitored and measured.



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