2

I understand what a VLAN is and what purpose it serves. However, I'm having a difficult time understanding where VLANs orginate.

Specifically, I know CISCO firewalls, switches, and routers all deal with VLANs: switches are configured with ports on certain VLANs, routers direct traffic between VLANs, and firewall block/allow traffic between VLANs.

But since I'm not an IT professional, where do the VLANs get managed/originated? Say I have VLAN 330 that has addresses between 192.168.1.0/24 and VLAN 331 that has addresses between 192.168.2.0/24. Where is this IP address range determined?

0
3

VLANs are layer-2 broadcast domains, and they have nothing to do with layer-3 (IP). VLANs do not have IP addresses. Using VLANs is like breaking a layer-2 switch into multiple, unconnected layer-2 switches.

Layer-3 interfaces are assigned IP addresses. It is up to the network administrator on how to assign IP addressing. For example, there could be a DHCP server, manually configured interfaces, or both, but that really has nothing to do with VLANs.

Most people will have a one-to-one relationship between the layer-2 VLANs and the layer-3 IP addressing by assigning every layer-3 interface connected to a VLAN with addressing in the same layer-3 network, but that is not a strict requirement. For example, I have seen a large server vendor address its servers with one network for data, one network for administrative access, and one network for a heartbeat between the servers, with all of that on a single VLAN.

Interfaces have IP addresses, VLANs do not.

0

Routers and Layer-3 switches manage VLANs. VLAN tags are local to the network. Your network can have VLAN 300 with IP address range 192.168.1.0/24, where as I can create VLAN 300 in my network with an IP address range of 192.168.30.0/25. When you create a VLAN tag of 300, you are creating a Layer-2 network. When you give that VLAN interface of VLAN tag 300 an IP address, you create an SVI (Switch Virtual Interface).

1
  • 1
    Wrong. VLANs are layer 2. Period. They have absolutely nothing to do with layer 3. VLANs do not have IP addresses. You're mixing up VLANs with VLAN Interfaces (SVI). – Jesse P. Sep 12 '20 at 15:45
0

Layer3 devies liks Routers , Firewalls, multi layered switch , Load balancers , and in layer2 switch VLANs can be created , delete and modification can be done ..

.As per business requirements and network traffic flow in setup VLans can created .

3
  • There is no L3 VLAN. The VLAN concept is L2 entirely. – Zac67 Dec 4 '20 at 17:33
  • While configuration inter-Vlan routing or SVi configuration L3 Vlan is created for example "switch(config)#interface vlan 10 , switch(config)# ip address 192.168.1.1 255.255.255.0 – Sagar Uragonda Dec 5 '20 at 2:57
  • 1
    You're mixing up VLAN and SVI - a Switch Virtual Interface is an interface to a VLAN. – Zac67 Dec 5 '20 at 9:24

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.