What is VLAN, why it is needed?, how it is used in real LAN environment, what will be the advantage of that?.
Also I have a server, which is sending some special packets over Network, how can I capture those packets and I need to send those packets to my application?. It is special packets, how can I differentiate from regular traffic?. Let me ask this way, if I want to send special packets to some other client, which is connected over LAN, how can I send those packets to that.
Thanks.
Santa, I would suggest doing some googling on 802.1q for help with VLANs and how they work. In very simple terms, 802.1q adds a 4 byte shim to the ethernet packet that contains VLAN ID information. This will allow
802.1q compliant switches to virtualize those packets to their own broadcast domain. Others might want to add another 2 cents. Or argue with my explanation. (:For packet captures, download ethereal and pcap and have fun. Start taking captures and put together all the pieces starting at layer 2 headers and work your way up through the frame. Have fun!
-mike
snipped-for-privacy@yahoo.com wrote:
Speaking of what is a VLAN...
How are they used by most switches? Our 3com switch 'learns' the VLAN addresses of anything connected to its ports, but theres no way to force a port to a VLAN. I thought one purpose of a vlan is security, but if I change my IP from 192.168.0.111 to 10.0.0.66 I can jump onto the class C address segment because the switch 'learns' my VLAN address.
Is there a list of switches and their VLAN functionality out there? Better still is there a specific word describing how to force a VLAN on a port?
Sounds as if you do not have vlans at all. Sounds as if you are simplty running multiple IP subnets on the same switch.
If you did not specify a vlan setup on the switch, then you are not using vlans (OK, there ARE ways to do it without configuring the switch, but that would assume A) you had network cards on all devices that allowed the cards to tag packets, and if you knew how to do that you would not be asking the above questions, and B) you would have to have a switch that has GARP enabled in it's default config, and I have never heard of such)
VLANS are layer two and have nothing at all to do with IP address.
In article , Ghazan Haider wrote: :Is there a list of switches and their VLAN functionality out there?
There isn't even a list of -manufacturers- of switches, let alone of what the details are for particular models.
Most probable your 3Com does not care about VLANs at all. Although there are Switches (namely Xylan/Alcatel) that use protocol based VLANs i.e. assign VLAN port mebership (layer 2) according to higher layer information contained in the packet, this is not the rule. A simple secondary address scheme could be the cause of what you encounter. The purpose of VLANs is flexibility, efficiency and maybe privacy. Security is a state of mind, not of technology.
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