Hello,
I am a network engineer that is highly visually dependent in order to understand how things work and has of course chosen the field with the most non-visual work: networking.
I think in drawings. I understand in drawings. Draw me something and there is a much higher chance of me understanding, instead of just explaining and/or writing.
As part of me setting up a network monitoring service called Solarwinds NPM, i had to create a (visual!) map overview of our network infrastructure. In the map, when creating links between two devices, i had to specify whether each end was ingress og egress:
That did not make sense to me. How can an interface be either one where traffic is coming in or one where traffic is coming out?
Fast forward to today, where i try to understand how to configure Flexible Netflow on a L2 switch, i see the following line in the Cisco docs: "You can apply Layer 2 NetFlow to the following interfaces for the ingress direction" which also did not make sense to me. Now it annoys me enough that i actually took time out to make this post.
I understand the concepts of ingress and egress; one is direction in and one is direction out. What i don't understand is how that can be applied to an interface, as in an interface can be specified as being an ingress interface or an egress interface, when all traffic are both entering and exiting the interface. I have made a small (visual!) presentation of the drawing in my head, that confuses me:
Here, we have 2 servers connected each interface on the same switch. Server A sends a packet to server B. The packet goes into interface A (ingress) and out of interface A (Egress) then through some internal logistics (as in what is this? who is it from? Where is it going? What interface is that server on? and so forth) then it goes into interface (ingress) and out of interface B (egress).
Which of the two interfaces are ingress and which is egress? Why?
I actually made a second packet on my drawing, but i think i've made my point. I'm sure that i have missed or misunderstood something.
I hope someone can help me clarify, preferably in a visual and easily understandable way.
