I`m struggling to fully understand some important piece of interface VLAN concept .It is a reason of configuring interface VLAN on multilayer switch. I guess I know the difference between Vlan and Interface Vlan, however can`t get the pieces together.
Please, find the GNS3 topology enclosed, taken from TSHOOT exam.
There`s a interface VLAN10 configured on DSW1. I`m trying to understand the reason. I got some theory, PLEASE confirm if my theory is correct.
if CLIENT1 is asking for address, it sends a packet to ASW1 with VLAN10 tag which is sent further to DSW1 through trunk. Then layer 2 information is stripped off and the packet is sent to R4 which functions as a DHCP server. Because the link between DSW1 and R4 is layer 3 and the information about VLAN10 is off (stripped off by DSW1), the interface VLAN10 is the only way for the R4 to know "somebody" from VLAN10 is asking for IP address. That means if interface VLAN10 wasn`t configured on DSW1, R4 wouldn`t know anything about VLAN10, meaning interface VLAN10 serves as a extension for VLAN10 layer 2. Which means if I had e.g. 100 VLANs on ASW1 I would have to configure 100 interface VLANs on DSW1 for the R4 to distinguish between different VLANs asking for the IP address.
would you mind uploading a screenshot of the topology? This should be more easy than downloading the whole GNS3 Project.
After only reading the text, i would guess that each VLAN interface on the DSW (Distribution Layer Switch?) has configured an IP-helper to ask R4s DHCP service for an anpropriate IP. In this secnario your assumption that you would need to create an VLAN interface for each existing VLAN on ASW (Access Layer Switch?) that shall get IP address information from the DHCP-server-service located on R4.
Thank you for your interest in this issue. You`re right about the IP-helper configured on DSW1. Please find the screenshot enclosed. I just thought somebody would want to take a look at the configuration for better understanding of my question, but maybe it`s not necessary.