Set DF flag on NAT-T keepalive packet
This commit
- Set the DF flag on the NAT-T keepalive packet
- Add comment for TTL value
- Do some cleanups
Bug: 196453719
Test: m
Change-Id: I401ae52d8f16e43120210cdea223fd251d53ea3b
diff --git a/framework/src/android/net/NattKeepalivePacketData.java b/framework/src/android/net/NattKeepalivePacketData.java
index d76f569..a18e713 100644
--- a/framework/src/android/net/NattKeepalivePacketData.java
+++ b/framework/src/android/net/NattKeepalivePacketData.java
@@ -72,23 +72,26 @@
Inet4Address srcAddress, int srcPort, Inet4Address dstAddress, int dstPort)
throws InvalidPacketException {
int length = IPV4_HEADER_LENGTH + UDP_HEADER_LENGTH + 1;
- ByteBuffer buf = ByteBuffer.allocate(length);
+ final ByteBuffer buf = ByteBuffer.allocate(length);
buf.order(ByteOrder.BIG_ENDIAN);
- buf.putShort((short) 0x4500); // IP version and TOS
+ buf.putShort((short) 0x4500); // IP version and TOS
buf.putShort((short) length);
- buf.putInt(0); // ID, flags, offset
- buf.put((byte) 64); // TTL
+ buf.putShort((short) 0); // ID
+ buf.putShort((short) 0x4000); // Flags(DF), offset
+ // Technically speaking, this should be reading/using the v4 sysctl
+ // /proc/sys/net/ipv4/ip_default_ttl. Use hard-coded 64 for simplicity.
+ buf.put((byte) 64); // TTL
buf.put((byte) OsConstants.IPPROTO_UDP);
int ipChecksumOffset = buf.position();
- buf.putShort((short) 0); // IP checksum
+ buf.putShort((short) 0); // IP checksum
buf.put(srcAddress.getAddress());
buf.put(dstAddress.getAddress());
buf.putShort((short) srcPort);
buf.putShort((short) dstPort);
- buf.putShort((short) (length - 20)); // UDP length
+ buf.putShort((short) (UDP_HEADER_LENGTH + 1)); // UDP length
int udpChecksumOffset = buf.position();
- buf.putShort((short) 0); // UDP checksum
- buf.put((byte) 0xff); // NAT-T keepalive
+ buf.putShort((short) 0); // UDP checksum
+ buf.put((byte) 0xff); // NAT-T keepalive
buf.putShort(ipChecksumOffset, IpUtils.ipChecksum(buf, 0));
buf.putShort(udpChecksumOffset, IpUtils.udpChecksum(buf, 0, IPV4_HEADER_LENGTH));