diff --git a/Makefile b/Makefile
index 9a98e14..efdbb2a 100644
--- a/Makefile
+++ b/Makefile
@@ -2,7 +2,7 @@ CXX=g++
 CXXFLAGS=-O2 -g -Wall -Wextra -std=c++17
 CXXLIBS=
 
-OBJS=UdpVpn.o VpnPeer.o TunDevice.o util.o main.o
+OBJS=UdpVpn.o VpnPeer.o TunDevice.o ip_header.o util.o main.o
 TARGET=congestvpn
 
 all: $(TARGET)
diff --git a/ip_header.cpp b/ip_header.cpp
new file mode 100644
index 0000000..6464266
--- /dev/null
+++ b/ip_header.cpp
@@ -0,0 +1,19 @@
+#include <cstring>
+
+#include "ip_header.hpp"
+#include "util.hpp"
+
+bool parse_ipv6_header(const char* data, size_t len, IPv6Header& header) {
+    if(len < 40) { // header too short
+        kdebugf("Bad v6 header -- too short.\n");
+        return false;
+    }
+    if((data[0] & 0xf0) != 0x60) { // bad version number
+        kdebugf("Bad v6 header -- bad version number (byte = %x).\n", data[0]);
+        return false;
+    }
+
+    memcpy(&(header.source), data + 8, 16);
+    memcpy(&(header.dest), data + 24, 16);
+    return true;
+}
diff --git a/ip_header.hpp b/ip_header.hpp
new file mode 100644
index 0000000..1d86666
--- /dev/null
+++ b/ip_header.hpp
@@ -0,0 +1,11 @@
+#pragma once
+
+#include <netinet/in.h>
+
+struct IPv6Header {
+    in6_addr source;
+    in6_addr dest;
+};
+
+/** Parse an IPv6 header, filling `header`. Returns `true` on success. */
+bool parse_ipv6_header(const char* data, size_t len, IPv6Header& header);