fix: use correct dhcp option for unicast dhcp renewal

fsgh42 · smira · commit 628487715649 · 2026-03-06T19:17:41.000+04:00
Talos attempts to do unicast DHCP renewal, if possible. However, if the DHCP server announces a PXE server in DHCP replies, talos erroneously send packets to this server, instead of the actual DHCP server. Because it falls back to broadcast, this issue did not surface. On networks where the PXE server has a different IP than the DHCP server (not uncommon in commercial and homelab setups), talos continuously logged this error: ``` got an error while processing the request: no matching response packet received ``` Use Option 54 (`server-identifier`) as the unicast destination, not `siaddr` (`ServerIPAddr`), which indicates the the PXE `next server` field (RFC 2131 §2) and is not the correct field to use in this context. Signed-off-by: Fritz Schaal <fritz.schaal@siderolabs.com> (cherry picked from commit 55b8721)
diff --git a/internal/app/machined/pkg/controllers/network/operator/dhcp4.go b/internal/app/machined/pkg/controllers/network/operator/dhcp4.go
@@ -463,15 +463,15 @@ func (d *DHCP4) parseNetworkConfigFromAck(ack *dhcpv4.DHCPv4, useHostname bool)
 func (d *DHCP4) newClient() (*nclient4.Client, error) {
 	var clientOpts []nclient4.ClientOpt
 
-	// We have an existing lease, target the server with unicast
-	if d.lease != nil && !d.lease.ACK.ServerIPAddr.IsUnspecified() {
+	// We have an existing lease, target the server with unicast.
+	if d.lease != nil && d.lease.ACK.ServerIdentifier() != nil {
 		// RFC 2131, section 4.3.2:
 		//     DHCPREQUEST generated during RENEWING state:
 		//     ... This message will be unicast, so no relay
 		//     agents will be involved in its transmission.
 		clientOpts = append(clientOpts,
 			nclient4.WithServerAddr(&net.UDPAddr{
-				IP:   d.lease.ACK.ServerIPAddr,
+				IP:   d.lease.ACK.ServerIdentifier(),
 				Port: nclient4.ServerPort,
 			}),
 			// WithUnicast must be specified manually, WithServerAddr is not enough
@@ -556,7 +556,7 @@ func (d *DHCP4) requestRenew(ctx context.Context, hostname network.HostnameStatu
 	addresses := d.AddressSpecs()
 
 	switch {
-	case d.lease != nil && !d.lease.ACK.ServerIPAddr.IsUnspecified():
+	case d.lease != nil && d.lease.ACK.ServerIdentifier() != nil:
 		d.logger.Debug("DHCP RENEW", zap.String("link", d.linkName))
 		d.lease, err = client.Renew(ctx, d.lease, mods...)
 	case d.lease != nil && d.lease.Offer != nil:
