CCisco 1242 & VLAN

Here is my equipment

CIsco 1242 AP
HP Procurve 1700 switch
linksys business class router RSV4000
windows 2003 server


i am new at the vlan thing and need some help. I want to create 2 SSID's on the G radio of my Cisco 1242AP. i know i need vlans. so how do i trunk this and how do i create another scope for DHCP if my router only has 1 gateway address? do i need another router to trunk to? i know i need to create a vlan for the new SSID but how do i trunk from the switch to the router and how do i give the clients of ssid2 an ip from network for guests when all the rest of my network is on network

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Jakob DigranesSenior ConsultantCommented:
Havent't got the config for Cisco in my head, haven't worked with those in a few years, but this is how it goes:

SSID1 - VLAN 10 - ip: CORP
SSID2 - VLAN 20 - ip: GUESTS

Linksys Router:
WAN port - public IP
Create both VLANs on router, with ip:
VLAN10: (DHCP 1)
VLAN20: (DHCP 2)
LAN Port: Connect to HP ProCurve 1700 on port 1

HP ProCurve.
Create the same VLANs, assign both VLANs to port 1
Set default VLAN 1 and chooes tagged only

Connect Cisco AP to a port configured similar to port 1
connect server to a port in VLAN 10 (ONLY) and choose untagged.

hope this helps.
My configs is for the ProCurve 2500series, but i guess it's similar with the 1700 ---


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mxrider_420Author Commented:
Thanks but i still dont know how to get the DHCP on the w2k3 server to know what vlan gets an ip for what vlan and what dhcp scope. and i also am confused about how you said management vlan. does that have to change? like i know i need vlan 50 on the AP to match vlan 50 on the switch and then trunk to vlan 50 on the router but i am unclear how to do this and what the difference between the tagging is and where to trunk it and what ports should be. thanks so very much for helping. if you can elaborate a bit it would be excellent thanks.
mxrider_420Author Commented:
also. my Linksys router doesnt allow for different DHCP to be served from it. it only allows 1 scope which is why i am using DHCP from wink2k3 server but i dont know how to give the new scope a gateway when the router only has 1 interface.
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Ken BooneNetwork ConsultantCommented:
Okay as far as dhcp goes, you need to set up the linkssys router on each vlan to have dhcp relay enabled.  There should be a check box for dhcp relay and then you will have a field to plug in the ip address of the dhcp server.  From a win2k perspective, you simply need to create the scopes, when the relay occurs, the router will send the ip address of the vlan that the request is coming from, and that is how the win2k dhcp server will know what scope to use.

As far as the trunking it should be like this.
On the AP set vlan 10 to be the native vlan.  Make sure you assign an ip address to the bvi1 inteface on the AP that will be on vlan 10.

On the port on the hp where the AP connects, you need to define that vlan 10 will be untagged and vlan 20 will be tagged.

One the port on the hp where the linksys router will connect, you need to define that vlan 10 will be untagged and vlan 20 will be tagged.

On the linksys router make sure you set up vlan 10 as the native vlan or the untagged vlan.  (cisco terminology for the untagged vlan is the native vlan, but not sure if linksys will show this as native or untagged.

Trunking is simply how you carry more than one vlan's traffic across an interface.  When you trunk the untagged vlans or the native vlans need to match,  you can only have one untagged vlan on a trunk, the rest of the vlans on the trunk will be tagged.

So the connection between the ap and the hp is a trunk and so is the connection from the linksys to the hp.

Hope that helps.
mxrider_420Author Commented:
This helps alot. my last question was with DHCP and how to provide a secondary scope for the non native vlan (20) from my win2k3 server. My Linksys router has dhcp forwarding on it but how will the server define what clients or vlans get what ip addresses? i need to make vlan 10 network (native) and vlan 20 guest or internet only, but if the DHCP is coming from the win2k3 server thats on the network (native) vlan how do i control the access and how does the second scope identify who gets what?

Ken BooneNetwork ConsultantCommented:
Ok so basically here is how it works.  DHCP requests are normally broadcast packets, which means they do not traverse a layer 3 boundary (router).  So if the dhcp server is on the 192.168.10.x network, and it receives a dhcp request that is a broadcast it knows that it needs to assign an ip address from the scope that matches its own network, i.e. 192.168.10.x.

Now since DHCP broadcasts do not traverse routers, in order for another network to send its DHCP request in to the DHCP server, we need to use DHCP Relays.  So what happens is the client on vlan 20, sends a broadcast DHCP request.  That broadcast hits the layer 3 vlan 20 interface on the router.  However, the router is configured to perform DHCP relay services and thereby takes the broadcast and sends a unicast packet to the DHCP server that is configured on the DHCP relay component.  So when it relays the packet it also puts in the network that the request came from, i.e. 192.168.20.x.  

Now when the dhcp server receives the relay it can see that the request is being made for an ip address on the 192.168.20.x scope so it will assign an ip address from that scope and send it back to the router that forwarded the DHCP relay.  That router will then pass on the DHCP response to the client on the 192.168.20.x network.

As far as the win2k server goes he doesn't know anything about what vlan something is on.  He only knows networks.  So the way the dhcp relay works, he will know what scope to use when assigning out addresses.

Does that help?
mxrider_420Author Commented:
Ok, this helps majorly. so basically i already have DHCP forwarded to the win2k3 server so this should be all set to go once i configure the vlans correctly. Now my only other inquiry is about what  if any vlan the win2k3 server needs to be on. or can it just stay on the default management one that its currently on or do i need trunking to the server too?

thanks so much your great help!
Ken BooneNetwork ConsultantCommented:
no the dhcp server can stay where its at.  no trunking to the dhcp server needed.
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