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New Member

DHCP and PXE question

Hello,

TOday we setup LINMIN (automated OS provisioning) for our server farm. We have about 350 servers, each server is on its own SEPARATE VLAN with a subnet of /29 for IP's. So every server has his own private vlan.

The dedicated servers are mostly in the 76.76.XX.XX /19 range and the LinMin server in the 208.66.XX.XX /24

Let's say for example the LinMin server is 208.66.111.111

Everything is connected to the main core switch (Cisco 6509).


We did some research and it seems like we have to implement the IP HELPER-ADDRESS command but it says to apply it on each vlan. I don't want to do that on 350 vlans and I do not think that is a good solution.

Is that the only solution or can I implement ip helpder-address on the cisco 6509 for the entire network ??

We do not run ANY other dhcp server as every server gets a static IP address.

On the cisco 6509, seems like there is in th econfiguration "no service dhcp" (thought I might add this detail in case I need to remove it to implement the new config I will have to put with the ip helper-address).

Please let me know if you have a solution

Thanks

7 REPLIES

Re: DHCP and PXE question

Hi,

I have never come across LINMIN before, but I am assuming that the LINMIN server provides an IP address to the servers in the other VLANs during teh provisioning process?

If this is the case then the only way I know how to do it would be to apply the IP helper-address command to each of the VLAN interfaces to allow the DHCP requests to pass through... As far as i know there is no way to globally provision an ip helper-address...

Many thanks

Jonathan

New Member

Re: DHCP and PXE question

Ok I removed the "no service dhcp" on the 6509 switch and added ip helpder address to the proper vlan in question, but it is still not picking up when booting from the network.

Anything else I can look at?

Thanks

Re: DHCP and PXE question

Hi,

Can you check the allocation of IP addresses using a test client (Laptop etc.) - something that is not trying to boot form the network. Is the DHCP server accessible from the switch? Do you have any Access Lists that could be stopping the DHCP packets from getting through?

Many thanks

Jonathan

New Member

Re: DHCP and PXE question

Hello,

thanks for the reply, but what do you mean by check the IP addresses allocations?

No access list on our switch

Yes the dhcp server pings fine from the 6509

Thanks

Cisco Employee

Re: DHCP and PXE question

As far as the "ip helper-address" is concerned, if you have a DHCP server AND a PXE server, then you would want two separate ip helper addresses configured on each l3 host facing interface in your network where they need to access those two servers.

The way this works, when on separate servers, is that the dhcp discover (send by the client) will need to that packet forwarded to the DHCP server AND the PXE server.

The DHCP server then responds with an ip address offer, and the PXE server responds with the PXE options telling the client where the server is located.

The client should recieve both DHCP offer replys, and then send a request to each server (DHCP to finalize the ip address assignment, and then PXE to get the actual  image location.

New Member

Re: DHCP and PXE question

Ok but they are the same IP. The PXE server runs as a DHCP server and they are on the same IP.

May I add that maybe the problem has to do with inter vlan talking? The two servers are on different vlans and their vlans are assign different IP subnets.

DHCP & PXE server: 208.66.XX.XXX

Server: 76.76.XX.XXX

So let's say the first part woks (dhcp server sees the dhcp request from the server), but then it will assign it a 208.66.XX.XXX from its dhcp pool of addresses, but that server is on its own Vlan and that vlan is not setup to be assigned 208.66 addresses but 76.76 so how will it communicate with it ?

Please help

Cisco Employee

Re: DHCP and PXE question

If the server is assigned an address (by design) that is not a part of that l3 subnet, then you need, at the very least, to give the switch a secondary address on that vlan, matching the server ip, so that basic routing can function correctly.

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