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Campus PXE config

jeff.cook
Level 1
Level 1

I'm wondering how you have chosen to get PXE to work in your environment. We are just stating with it and I am getting conflicting info.

The server people say I have to set ip helper-address, but a lot of the documentation I'm finding says just set the option on the DHCP server.

I'm sure both will work (if configured correctly) but what is normal/standard. What did you you?

Thank You

2 Replies 2

Giuseppe Larosa
Hall of Fame
Hall of Fame

Hello Jeff,

we need to set the additional helper-address for the RIS server(s).

The reason is that the PXE process uses DHCP messages to reach also the PXE server (RIS server).

spanning-tree portfast is also needed on the port.

We do this on demand: the field technician that needs to rebuild a PC on site first tries to perform a PXE boot, if it doesn't work it he/she calls the NOC asking for it.

To be noted that in case of remote branch offices with low speed links can be faster to carry the PC to a bigger better connected office: we have been reported of an 18 hours time to rebuild a PC that was in a branch with only an IPSEC vpn connection to the intranet.

There was a recent thread where possible issues when DHCP snooping is enabled have been analyzed.

There was a bug in first DHCP snooping implementations that caused issues with PXE.

Hope to help

Giuseppe

We're using Microsoft RIS and had problems when the IP Helper on the VLAN pointed to a host address. We changed the IP Helper so that it pointed to the destination subnet broadcast address and it worked a treat.

From the sniffer traces we did it would appear that for RIS to respond to a PXE request both the DHCP server and the RIS Server have to "hear" the request. The DHCP server repsonds with an address and the RIS server responds with a PXE reply that carries a NULL ip address.

If RIS is running on the same server as DHCP then you'll be OK with the IP helper pointing directly at the host address.

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