topic Re: PXE boot on SDA not working in Software-Defined Access (SD-Access)

PXE boot on SDA not working

HAT — Tue, 18 Jul 2023 12:06:02 GMT

Hi All

I m working on setting up PXE boot for SCCM device builds over the network . We are using an SDA network where I have configured IP helper on the SVI the endpoints are connected to . This is the configuration on the Fabric Edge node

SDA-EDGE-POC-1#sh run interface vlan 1025
Building configuration...

Current configuration : 397 bytes
!
interface Vlan1025
description Configured from Cisco DNA-Center
mac-address 0000.xxx.f65d
vrf forwarding Corporate_VN_POC
ip address 10.223.7.1 255.255.255.0
ip helper-address 172.28.251.10   <------------ DHCP Server ( Cisco 3650 switch )
ip helper-address 172.28.86.174   <------------ SCCM Server
ip helper-address 172.28.86.175   <------------ SCCM Server
no ip redirects
ip route-cache same-interface
no lisp mobility liveness test
lisp mobility 10_223_7_0-Corporate_VN_POC-IPV4
end

I m unable to get it working - stuck on the "start pxe over ipv4" screen . As per the attached pcap it look like it doesn't even go past the DHCP Discovery process . However I can also successfully obtain an IP address from the expected DHCP pool while connecting a random device to the same interface . I can then assume routing is not an issue here .

I have not used any DHCP Options as the the IP helper method appears to be the recommendation when the DHCP/SCCM server sit on a different subnet .

Can you please assist ?

Thanks in advance

Re: PXE boot on SDA not working

jalejand — Wed, 12 Jul 2023 16:56:53 GMT

Helpering in a fabric overlay (call it SDA, ACI, etc) with anycast gateways is useless unless the protocol has understanding of the real source of the relay (ex DHCP Opt 82).

There are two ways of achieving this:

1) Using DHCP Option 66 and 67
2) Using Proxy DHCP so the SCCM server acts as DHCP server (using unicast DHCP directly to the SCCM server, where options aren't needed).

But you seem to be having problems with the very initial DHCP of the PXE device; just wondering, is your fabric using collocated Border+CP or separated roles?

Re: PXE boot on SDA not working

HAT — Fri, 14 Jul 2023 09:07:16 GMT

Hi Jalejand

Thanks for the reply , the fabric is collocated ( CP + Border ) . I have read that using DHCP options was not recommended so opted for IP helpers instead .

PXE boot is working on our Nexus based User Access network though but not on SDA .

I have changed the config by removing the SCCM server IP address from the SVI config on the Fabric Edge and configured the DHCP server with the SCCM server IP address as the next server , also used Options 60 which seemed to have got me further by obtaining an IP address from the DHCP server but failed to download the NBP file ( Please see attachment ) .

DHCP server config

ip dhcp pool Desktop-Build
network 10.223.7.0 255.255.255.0
next-server 172.28.86.174 <------------ SCCM Server
domain-name xxxx-xx.xxxx.loc
dns-server 172.28.64.10 172.28.65.10
default-router 10.223.7.1
option 60 ascii "PXEClient"
lease 0 8

Any assistance would be greatly appreciated

Thanks

Re: PXE boot on SDA not working

Andrii Oliinyk — Tue, 25 Jul 2023 14:12:51 GMT

i'm pretty sure your PXE-devices denies image it downloads by tftp in the PXE-stage

Re: PXE boot on SDA not working

Andrii Oliinyk — Mon, 18 Nov 2024 09:59:06 GMT

u might already resolved issue, but just for the case:
if 172.28.86.174 lives in the Fabric overlay as EID, it wont work at all

Re: PXE boot on SDA not working

djbillingsley — Mon, 13 Apr 2026 01:16:26 GMT

Had a similar issue, turned off DHCP snooping on the switch connected to the SCCM server and it was able to then use the IP vs the MAC address to find the requesting PXE client on the fabric.

Re: PXE boot on SDA not working

nathanmonteyne0 — Thu, 23 Apr 2026 08:25:16 GMT

We also had issues with this don't know exactly what the complete fix was but the main thing we had is that we needed to do switchport access VLAN x on the access ports otherwise it wouldn't work

Re: PXE boot on SDA not working

HAT — Thu, 23 Apr 2026 13:05:51 GMT

Our fix was to upgrade the SCCM server . Thanks All