Can you have multiple subnets on one vlan?
Ex.
subnet 192.168.1.0 and subnet 192.168.2.0 on VLAN 1
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Can you have multiple subnets on one vlan?
Ex.
subnet 192.168.1.0 and subnet 192.168.2.0 on VLAN 1
yeap, but it is odd, inst it? why on same (virtual) lan you want 2 diferent ip networks?
Yes it is odd, I was just wondering because if two subnets are on one vlan and since it is possible, that would mean you would see broadcasts from both subnets which seems really weird to me. I have never seen that before.
Its the same of putting 2 diferent sets of ip (diferent networks) on same lan segment. you can do it. but you can have "weird" effects....
Am I missing something here? A VLAN is a broadcast domain; how can it have more than one subnet, thereby implying more than one broadcast domain? Wouldn't this screw everything up, not just have "weird" effects?
And how do you put several different ip networks on the same lan without dividing them into vlans? :confused:
Ok now i'm more confused? Can you have two subnets on the same vlan or not?
the reason i asked in the first place is because I saw on example on a webpage where
ip address 192.168.1.0 was on VLAN 40 and 192.168.2.0 was also on VLAN 40 and then one of them got moved to a different VLAN.
SO i would love to know for sure if this is possible or not?
Look at the definition. http://www.webopedia.com/TERM/V/VLAN.html
VLANs can be subnets or supernets (http://www.webopedia.com/TERM/C/CIDR.html). So technically you could have 192.168.1.0 - 192.168.15.0 on the same VLAN. Kind of a big broadcast domain, but it'd work. If you split the network up due to growth and the fact that someone didn't think about it too much then you could have a scenario where you need to move hosts to a different VLAN. Seems to me to be bad planning.
Great thanks!
No, it would still be a single broadcast domain: a broadcast domain only represents the "area" in which a broadcast will propagate. There's nothing to say that these broadcasts must concern a single subnet. In fact, broadcast domains are layer 2 entities while subnets are layer 3 entities so they have no real interdependencies...Quote:
Originally posted here by KeyserSoze
Am I missing something here? A VLAN is a broadcast domain; how can it have more than one subnet, thereby implying more than one broadcast domain? Wouldn't this screw everything up, not just have "weird" effects?
And how do you put several different ip networks on the same lan without dividing them into vlans? :confused:
As to having multiple subnets on the same lan segment, it wouldn't be any diffrent than a lan segment that connects two routers that route multiple subnets. What would happen is that all hosts on the lan would receive every subnet's packets but the routing software of every hosts would drop packets that aren't destined to the subnet it is a "member" of since there wouldn't be any local routes for them (or, supposing ipforwarding is enabled, it would send them to the default gateway).
Ammo
What are the subnetmasks? There's no way to tell if these are 2 subnets or just 1.Quote:
Originally posted here by thekit
ip address 192.168.1.0 was on VLAN 40 and 192.168.2.0 was also on VLAN 40 and then one of them got moved to a different VLAN.
If the subnetmask is 255.255.255.0 it's 2 subnets but if it's 255.255.252.0 it's 1 subnet.
The short answer is yes. depending on what you wish to accomplish, you can go the other route and make your broadcast domain as small as possible. where you can define certain ports on a switch (cisco 4507R <---- sup mod engine) to a particular subnet range example fa0/1 - fa0/20 = 10.0.0.1 - 10.0.0.20. the next 20 ports will equal the next 20 ips in subnet etc. more admin work, but in the end worth it. in cisco case (i do not know 3com or the others except nortel, and lo I am not impressed by it)
vlsm (variable length subnet masks) are definable within the vlans
i realise that this does fall slightly outside the question's scope but consider these as well:
rename your vlans (dont use 1 and 2)
place your infrastructure devices and others such as servers in their own vlans
make your broadcast domains as small as possible
kill unnecessary traffic, and if possible use ids ..........
Lemme try this.
If Vlan 40 includes 192.168.1.0 and 192.168.2.0 then the mask for the VLAN will be /23 or 255.255.254.0.
512 addresses - 2 (network address of 192.168.1.0 and broadcast address of 192.168.2.255)
Supernets are used in large enterprise networks with large switch fabrics. I see them everyday.
hth
catman
Actually it's /22 or 255.255.252.0. /23 would only include 192.168.0.x and 192.168.1.x (192.168.2.x and 192.168.3.x would be the next subnet).Quote:
Originally posted here by catman
If Vlan 40 includes 192.168.1.0 and 192.168.2.0 then the mask for the VLAN will be /23 or 255.255.254.0.
Can you have more then one subnet on a VLAN? YES.
Why would you do this? In one situation I can think of, you may need extra IP addresses for increased network capacity without adding additional router blades. If you Run out of slots in your router chasse you may resort to doing this as well. Secondary IP addresses on a router interface are used when security is not a concern.
You'll need that router (blade) anyway. How else would you get out of a VLAN?Quote:
In one situation I can think of, you may need extra IP addresses for increased network capacity without adding router blades.
"Router-on-a-stick" style...Quote:
Originally posted here by SirDice
You'll need that router (blade) anyway. How else would you get out of a VLAN?
If you already have a router connected you don't necessarly need another router port.
That being said, anything involving multiple subnets on the same (virtual or not) lan segment (except routing trunks) is rather odd and should probably be redesigned because there surely (absoloutly!) is a better way of doing it...
ie: YES it CAN be done, NO it (probably) shouldn't be done.
Ammo