Inter VLAN Routing question

[Nico_24]

Hello,

because of our interest in purchasing a 2600 series Switch, I have the following questions:

- is it possible to put each switchport in it's own vlan with inter vlan routing between them if the IPs come from the same subnet?
If not, can I make small subnets out of a (e.g.) /24 like /31 or /32 without being able to configure the router?
- what does the limitation of 16 routes of those switches mean in practice, especially in the scenary mentioned above?

Thanks & regards,
Nico

[Ron Kinner · Accepted solution]

- is it possible to put each switchport in its own vlan with inter vlan routing between them if the IPs come from the same subnet?

Not if you use standard VLANs. They would need to be in separate subnets.

If not, can I make small subnets out of a (e.g.) /24 like /31 or /32 without being able to configure the router?

Yes. If the 2626 is doing routing and the router at least knows that the major net can be reached via the 2626 then that's all it needs to know. The 2626 will do the routing. Users must use the IP address of the 2626 in their VLAN as their gateway to get to the router.

- what does the limitation of 16 routes of those switches mean in practice, especially in the scenary mentioned above?

Nothing. The 2626 will automatically know about the subnets in its own VLANs so no statics are required for them. Statics are only used if you need to tell it about a network that is not directly connected. Say the router is connected to the internet then you might want to add 1 static:

ip route 0.0.0.0 0.0.0.0 routersIPaddress

Ron

[Nico_24]

Thanks for your great answer. Everything is much more clear to me now.
I guess I will do it with the seperate vlans and routing via the switch, though this means a lot of lost IPs in small subnets ;)
Just one more question: is it possible to use the same dhcp server on each vlan?

Thanks & regards,
Nico

[Ron Kinner]

Possible but not easy. How is the DHCP server supposed to know what VLAN they are coming from? If you had one that could accept 802.1q tagging then it would know where they were and could assign them that way or if it had a NIC for each VLAN (very wasteful). Otherwise I think you have to know the MAC ahead of time tho there are a few other tricks. See:

http://tcpmag.com/qanda/article.asp?EditorialsID=285

Ron

[Nico_24]

Thank you very much, that thing with the ip helper seems to fit my needs.
Just to explain: I need all that for a classical housing environment which I want to be secure for me and my customers. If you know a better solution, feel free to tell me :)
Thanks so far.

Regards,
Nico

[Marcus Augustus_1]

With regard to your question about dhcp for different vlan's, I set up something like that years ago. You can get a "VLAN-aware" NIC (I used Intel's) for the dhcp-server, then it works pretty much "automagically", just make sure the port it is on participates in all the VLAN's you have.

HTH,

Marcus

[Nico_24]

And there may be pretty much vlans, so that's not really a possible solution, but thanks anyway ;)

[Ron Kinner]

Nico,

You might look into Isolated Port Groups which is available on 2500 series with the latest release of software.

See page 12 (22 of 264) of the very slow loading adobe file:

ftp://ftp.hp.com/pub/networking/software/59903102-e3.pdf

Ron

[Nico_24]

Hi,

yes I know that feature. The problem is that the "private" ports cannot communicate with other servers on the same switch. This might be necessary in some cases.

Regards,
Nico

[Kell van Daal]

Regarding the DHCP issue.
You don't need any extra hardware for it.
You can enable dhcp relay on the switch (check commands dhcp-relay and in vlan conf ip helper-address).
You only need one DHCP-server in one VLAN, which will have scopes for all the subnets. The VLAN's configured with a helper-address sees a DHCP request, and then forwards it (unicast) to the DHCP server. Because the request is send unicast, the DHCP server can determine what scope is needed for the request. The DHCP server sends its offer back to the switch, which will forward again to the client.