You can have 2 PCs in 2 Different VLAN with IPs in same subnet
With VLAN created on a switch, the Switch creates a table called as the CAM table which keeps a map of the Switch Port Mac address, Connected PC's Mac Address & the VLAN ID apped to it.
Now lets assume 2 PCs connected to 2 different VLANs. with IP in the same Subnet. Now from PC 1 you are sending a PING to the other PC. Now a switch being a Data Link Device will first confirm whether the source & the destination MAC in the ICMP frame belong to the same VLAN. i this case it's not so the switch wiill not forward the frame.
You can also have 2 different PCs in 2 different VLAN having same IP.
When you assign a Static Ip to a PC, the PC before applying the IPs to the TCP/IP, it will generate GARP to its own IP address. If it gets a reply then it pops up with a IP conflict error other wise it applies the IP addrerss
Now in this instance there won't be any reply for the GARP Request because the Layer 2 Broad cast will be propagated to its member VLAN ports & the PC will accept the IP address
That's what I thought. But I'm having MSSC (or whatever - you know, the certified engineers) telling me no, I must sub-net as well.
I certainly won't design my VLANs with identical IPs. I will have to place a layer3 switch to perform cross routing to printers and the internets access, and so identical IPs could become problematical, although I don't know that for sure.
I'm thinking that since I'm so wet behind the ears for all this that I will put the printers and the internet access on their own VLAN so that if I make a mistake the damage will be kept to a minimum. Printers do not launch hack attacks in the general run of things.
Thank you so much, that question has been driving me nuts.
Re: Layer 2 Vlan why IP range change?
12 years 8 months ago #12520