From 3108669ecd14d028ed111c9e499292c960329e8c Mon Sep 17 00:00:00 2001
From: Simon Moser <mosers@tf.uni-freiburg.de>
Date: Mon, 29 Nov 2021 14:20:03 +0100
Subject: [PATCH] Handle DHCP edge case [Fix #9]

---
 proxy/main.go | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/proxy/main.go b/proxy/main.go
index f44e4ce..09821e1 100644
--- a/proxy/main.go
+++ b/proxy/main.go
@@ -315,9 +315,15 @@ func handleDHCP(content []byte, dstMAC net.HardwareAddr, srcMAC net.HardwareAddr
 		switch reqType {
 		case dhcp4.Discover:
 			if OldIP == nil {
-				log.Fatal(prefix, "DHCPDISCOVER but not previous address is known")
+				if NewIP == nil || !NewIP.IsGlobalUnicast() {
+					log.Warning(prefix, "DHCP request, but neither OldIP nor NewIP known")
+					sendDHCPRequest(dhcp4.Discover, net.IPv4zero)
+					return
+				}
+				sendDHCPReply(req, dhcp4.Offer, NewIP, options, dstMAC)
+			} else {
+				sendDHCPReply(req, dhcp4.Offer, OldIP, options, dstMAC)
 			}
-			sendDHCPReply(req, dhcp4.Offer, OldIP, options, dstMAC)
 		case dhcp4.Inform:
 			fallthrough
 		case dhcp4.Request: