diff --git a/src/probe_modules/module_bacnet.c b/src/probe_modules/module_bacnet.c
index 06534fb98..3d747b117 100644
--- a/src/probe_modules/module_bacnet.c
+++ b/src/probe_modules/module_bacnet.c
@@ -37,7 +37,16 @@ static inline uint8_t get_invoke_id(uint32_t *validation)
 	return (uint8_t)((validation[1] >> 24) & 0xFF);
 }
 
-int bacnet_init_perthread(void *buf, macaddr_t *src, macaddr_t *gw, void **arg)
+int bacnet_init_perthread(void **arg)
+{
+	uint32_t seed = aesrand_getword(zconf.aes);
+	aesrand_t *aes = aesrand_init_from_seed(seed);
+	*arg = aes;
+
+	return EXIT_SUCCESS;
+}
+
+int bacnet_prepare_packet(void *buf, macaddr_t *src, macaddr_t *gw, UNUSED void *arg)
 {
 	memset(buf, 0, MAX_PACKET_SIZE);
 	struct ether_header *eth_header = (struct ether_header *)buf;
@@ -67,10 +76,6 @@ int bacnet_init_perthread(void *buf, macaddr_t *src, macaddr_t *gw, void **arg)
 	bnp->apdu.server_choice = 0x0c;
 	memcpy(body, bacnet_body, BACNET_BODY_LEN);
 
-	uint32_t seed = aesrand_getword(zconf.aes);
-	aesrand_t *aes = aesrand_init_from_seed(seed);
-	*arg = aes;
-
 	return EXIT_SUCCESS;
 }
 
@@ -184,8 +189,9 @@ probe_module_t module_bacnet = {.name = "bacnet",
 				.pcap_filter = "udp || icmp",
 				.pcap_snaplen = 1500,
 				.port_args = 1,
-				.thread_initialize = &bacnet_init_perthread,
 				.global_initialize = &bacnet_global_initialize,
+				.thread_initialize = &bacnet_init_perthread,
+				.prepare_packet = &bacnet_prepare_packet,
 				.make_packet = &bacnet_make_packet,
 				.print_packet = &udp_print_packet,
 				.validate_packet = &bacnet_validate_packet,
diff --git a/src/probe_modules/module_dns.c b/src/probe_modules/module_dns.c
index 43f244ac5..1d60b9d1e 100644
--- a/src/probe_modules/module_dns.c
+++ b/src/probe_modules/module_dns.c
@@ -735,8 +735,8 @@ static int dns_global_cleanup(UNUSED struct state_conf *zconf,
 	return EXIT_SUCCESS;
 }
 
-int dns_init_perthread(void *buf, macaddr_t *src, macaddr_t *gw,
-		       UNUSED void **arg_ptr)
+int dns_prepare_packet(void *buf, macaddr_t *src, macaddr_t *gw,
+		       UNUSED void *arg_ptr)
 {
 	memset(buf, 0, MAX_PACKET_SIZE);
 
@@ -902,7 +902,7 @@ void dns_add_null_fs(fieldset_t *fs)
 
 void dns_process_packet(const u_char *packet, uint32_t len, fieldset_t *fs,
 			uint32_t *validation,
-			__attribute__((unused)) struct timespec ts)
+			UNUSED struct timespec ts)
 {
 	struct ip *ip_hdr = (struct ip *)&packet[sizeof(struct ether_header)];
 	if (ip_hdr->ip_p == IPPROTO_UDP) {
@@ -1111,8 +1111,8 @@ probe_module_t module_dns = {
     .pcap_filter = "udp || icmp",
     .pcap_snaplen = PCAP_SNAPLEN,
     .port_args = 1,
-    .thread_initialize = &dns_init_perthread,
     .global_initialize = &dns_global_initialize,
+    .prepare_packet = &dns_prepare_packet,
     .make_packet = &dns_make_packet,
     .print_packet = &dns_print_packet,
     .validate_packet = &dns_validate_packet,
diff --git a/src/probe_modules/module_icmp_echo.c b/src/probe_modules/module_icmp_echo.c
index aa51a916c..a7f8f7533 100644
--- a/src/probe_modules/module_icmp_echo.c
+++ b/src/probe_modules/module_icmp_echo.c
@@ -137,8 +137,8 @@ int icmp_global_cleanup(__attribute__((unused)) struct state_conf *zconf,
 	return EXIT_SUCCESS;
 }
 
-static int icmp_echo_init_perthread(void *buf, macaddr_t *src, macaddr_t *gw,
-				    UNUSED void **arg_ptr)
+static int icmp_echo_prepare_packet(void *buf, macaddr_t *src, macaddr_t *gw,
+				    UNUSED void *arg_ptr)
 {
 	memset(buf, 0, MAX_PACKET_SIZE);
 
@@ -330,7 +330,7 @@ probe_module_t module_icmp_echo = {
     .port_args = 0,
     .global_initialize = &icmp_global_initialize,
     .close = &icmp_global_cleanup,
-    .thread_initialize = &icmp_echo_init_perthread,
+    .prepare_packet = &icmp_echo_prepare_packet,
     .make_packet = &icmp_echo_make_packet,
     .print_packet = &icmp_echo_print_packet,
     .process_packet = &icmp_echo_process_packet,
diff --git a/src/probe_modules/module_icmp_echo_time.c b/src/probe_modules/module_icmp_echo_time.c
index dcac00c47..a18b6bc58 100644
--- a/src/probe_modules/module_icmp_echo_time.c
+++ b/src/probe_modules/module_icmp_echo_time.c
@@ -34,8 +34,8 @@ struct icmp_payload_for_rtt {
 	ipaddr_n_t dst;
 };
 
-static int icmp_echo_init_perthread(void *buf, macaddr_t *src, macaddr_t *gw,
-				    UNUSED void **arg_ptr)
+static int icmp_echo_prepare_packet(void *buf, macaddr_t *src, macaddr_t *gw,
+				    UNUSED void *arg_ptr)
 {
 	memset(buf, 0, MAX_PACKET_SIZE);
 
@@ -259,7 +259,7 @@ probe_module_t module_icmp_echo_time = {
     .pcap_filter = "icmp and icmp[0]!=8",
     .pcap_snaplen = 96,
     .port_args = 0,
-    .thread_initialize = &icmp_echo_init_perthread,
+    .prepare_packet = &icmp_echo_prepare_packet,
     .make_packet = &icmp_echo_make_packet,
     .print_packet = &icmp_echo_print_packet,
     .process_packet = &icmp_echo_process_packet,
diff --git a/src/probe_modules/module_ipip.c b/src/probe_modules/module_ipip.c
index fa082f96d..8251e24e8 100644
--- a/src/probe_modules/module_ipip.c
+++ b/src/probe_modules/module_ipip.c
@@ -133,8 +133,8 @@ int ipip_global_cleanup(UNUSED struct state_conf *zconf,
 	return EXIT_SUCCESS;
 }
 
-int ipip_init_perthread(void *buf, macaddr_t *src, macaddr_t *gw,
-			UNUSED void **arg_ptr)
+int ipip_prepare_packet(void *buf, macaddr_t *src, macaddr_t *gw,
+			UNUSED void *arg_ptr)
 {
 	memset(buf, 0, MAX_PACKET_SIZE);
 	struct ether_header *eth_header = (struct ether_header *)buf;
@@ -403,8 +403,8 @@ probe_module_t module_ipip = {
     .pcap_filter = "udp || icmp",
     .pcap_snaplen = 1500,
     .port_args = 1,
-    .thread_initialize = &ipip_init_perthread,
     .global_initialize = &ipip_global_initialize,
+    .prepare_packet = &ipip_prepare_packet,
     .make_packet = &ipip_make_packet,
     .print_packet = &ipip_print_packet,
     .validate_packet = &ipip_validate_packet,
diff --git a/src/probe_modules/module_ntp.c b/src/probe_modules/module_ntp.c
index a7ccc1d8c..34d813914 100644
--- a/src/probe_modules/module_ntp.c
+++ b/src/probe_modules/module_ntp.c
@@ -154,7 +154,16 @@ void ntp_process_packet(const u_char *packet, UNUSED uint32_t len,
 	}
 }
 
-int ntp_init_perthread(void *buf, macaddr_t *src, macaddr_t *gw, void **arg)
+int ntp_init_perthread(void **arg)
+{
+	uint32_t seed = aesrand_getword(zconf.aes);
+	aesrand_t *aes = aesrand_init_from_seed(seed);
+	*arg = aes;
+
+	return EXIT_SUCCESS;
+}
+
+int ntp_prepare_packet(void *buf, macaddr_t *src, macaddr_t *gw, UNUSED void *arg)
 {
 	memset(buf, 0, MAX_PACKET_SIZE);
 	struct ether_header *eth_header = (struct ether_header *)buf;
@@ -176,10 +185,6 @@ int ntp_init_perthread(void *buf, macaddr_t *src, macaddr_t *gw, void **arg)
 			    sizeof(struct udphdr) + sizeof(struct ntphdr);
 	module_ntp.max_packet_length = header_len;
 
-	uint32_t seed = aesrand_getword(zconf.aes);
-	aesrand_t *aes = aesrand_init_from_seed(seed);
-	*arg = aes;
-
 	return EXIT_SUCCESS;
 }
 
@@ -240,8 +245,9 @@ probe_module_t module_ntp = {.name = "ntp",
 			     .pcap_filter = "udp || icmp",
 			     .pcap_snaplen = 1500,
 			     .port_args = 1,
-			     .thread_initialize = &ntp_init_perthread,
 			     .global_initialize = &ntp_global_initialize,
+			     .thread_initialize = &ntp_init_perthread,
+			     .prepare_packet = &ntp_prepare_packet,
 			     .make_packet = &udp_make_packet,
 			     .print_packet = &ntp_print_packet,
 			     .validate_packet = &ntp_validate_packet,
diff --git a/src/probe_modules/module_tcp_synackscan.c b/src/probe_modules/module_tcp_synackscan.c
index cc43334c5..78734468e 100644
--- a/src/probe_modules/module_tcp_synackscan.c
+++ b/src/probe_modules/module_tcp_synackscan.c
@@ -34,8 +34,8 @@ static int synackscan_global_initialize(struct state_conf *state)
 	return EXIT_SUCCESS;
 }
 
-static int synackscan_init_perthread(void *buf, macaddr_t *src, macaddr_t *gw,
-				     UNUSED void **arg_ptr)
+static int synackscan_prepare_packet(void *buf, macaddr_t *src, macaddr_t *gw,
+				     UNUSED void *arg_ptr)
 {
 	memset(buf, 0, MAX_PACKET_SIZE);
 	struct ether_header *eth_header = (struct ether_header *)buf;
@@ -211,7 +211,7 @@ probe_module_t module_tcp_synackscan = {
     .pcap_snaplen = 96,
     .port_args = 1,
     .global_initialize = &synackscan_global_initialize,
-    .thread_initialize = &synackscan_init_perthread,
+    .prepare_packet = &synackscan_prepare_packet,
     .make_packet = &synackscan_make_packet,
     .print_packet = &synscan_print_packet,
     .process_packet = &synackscan_process_packet,
diff --git a/src/probe_modules/module_tcp_synscan.c b/src/probe_modules/module_tcp_synscan.c
index 2222b55d8..b9311e787 100644
--- a/src/probe_modules/module_tcp_synscan.c
+++ b/src/probe_modules/module_tcp_synscan.c
@@ -74,8 +74,8 @@ static int synscan_global_initialize(struct state_conf *state)
 	return EXIT_SUCCESS;
 }
 
-static int synscan_init_perthread(void *buf, macaddr_t *src, macaddr_t *gw,
-				  UNUSED void **arg_ptr)
+static int synscan_prepare_packet(void *buf, macaddr_t *src, macaddr_t *gw,
+				  UNUSED void *arg_ptr)
 {
 	struct ether_header *eth_header = (struct ether_header *)buf;
 	make_eth_header(eth_header, src, gw);
@@ -259,7 +259,7 @@ probe_module_t module_tcp_synscan = {
     .pcap_snaplen = 96,
     .port_args = 1,
     .global_initialize = &synscan_global_initialize,
-    .thread_initialize = &synscan_init_perthread,
+    .prepare_packet = &synscan_prepare_packet,
     .make_packet = &synscan_make_packet,
     .print_packet = &synscan_print_packet,
     .process_packet = &synscan_process_packet,
diff --git a/src/probe_modules/module_udp.c b/src/probe_modules/module_udp.c
index bee16174a..f0a6f202e 100644
--- a/src/probe_modules/module_udp.c
+++ b/src/probe_modules/module_udp.c
@@ -241,7 +241,17 @@ int udp_global_cleanup(UNUSED struct state_conf *zconf,
 	return EXIT_SUCCESS;
 }
 
-int udp_init_perthread(void *buf, macaddr_t *src, macaddr_t *gw, void **arg_ptr)
+int udp_init_perthread(void **arg_ptr)
+{
+	// Seed our random number generator with the global generator
+	uint32_t seed = aesrand_getword(zconf.aes);
+	aesrand_t *aes = aesrand_init_from_seed(seed);
+	*arg_ptr = aes;
+
+	return EXIT_SUCCESS;
+}
+
+int udp_prepare_packet(void *buf, macaddr_t *src, macaddr_t *gw, UNUSED void *arg_ptr)
 {
 	memset(buf, 0, MAX_PACKET_SIZE);
 	struct ether_header *eth_header = (struct ether_header *)buf;
@@ -260,11 +270,6 @@ int udp_init_perthread(void *buf, macaddr_t *src, macaddr_t *gw, void **arg_ptr)
 		memcpy(payload, udp_fixed_payload, udp_fixed_payload_len);
 	}
 
-	// Seed our random number generator with the global generator
-	uint32_t seed = aesrand_getword(zconf.aes);
-	aesrand_t *aes = aesrand_init_from_seed(seed);
-	*arg_ptr = aes;
-
 	return EXIT_SUCCESS;
 }
 
@@ -857,8 +862,9 @@ probe_module_t module_udp = {
     .pcap_snaplen =
 	MAX_UDP_PAYLOAD_LEN + 20 + 24, // Ether Header, IP Header with Options
     .port_args = 1,
-    .thread_initialize = &udp_init_perthread,
     .global_initialize = &udp_global_initialize,
+    .thread_initialize = &udp_init_perthread,
+    .prepare_packet = &udp_prepare_packet,
     .make_packet =
 	&udp_make_packet, // can be overridden to udp_make_templated_packet by udp_global_initalize
     .print_packet = &udp_print_packet,
diff --git a/src/probe_modules/module_upnp.c b/src/probe_modules/module_upnp.c
index c778e6377..b07e318ff 100644
--- a/src/probe_modules/module_upnp.c
+++ b/src/probe_modules/module_upnp.c
@@ -39,8 +39,8 @@ int upnp_global_initialize(struct state_conf *state)
 	return EXIT_SUCCESS;
 }
 
-int upnp_init_perthread(void *buf, macaddr_t *src, macaddr_t *gw,
-			UNUSED void **arg_ptr)
+int upnp_prepare_packet(void *buf, macaddr_t *src, macaddr_t *gw,
+			UNUSED void *arg_ptr)
 {
 	memset(buf, 0, MAX_PACKET_SIZE);
 	struct ether_header *eth_header = (struct ether_header *)buf;
@@ -255,7 +255,7 @@ probe_module_t module_upnp = {
     .pcap_snaplen = 2048,
     .port_args = 1,
     .global_initialize = &upnp_global_initialize,
-    .thread_initialize = &upnp_init_perthread,
+    .prepare_packet = &upnp_prepare_packet,
     .make_packet = &udp_make_packet,
     .print_packet = &udp_print_packet,
     .process_packet = &upnp_process_packet,
diff --git a/src/probe_modules/probe_modules.h b/src/probe_modules/probe_modules.h
index 2b393a268..ecfd43ede 100644
--- a/src/probe_modules/probe_modules.h
+++ b/src/probe_modules/probe_modules.h
@@ -30,14 +30,28 @@ typedef struct probe_response_type {
 
 typedef int (*probe_global_init_cb)(struct state_conf *);
 
-typedef int (*probe_thread_init_cb)(void *packetbuf, macaddr_t *src_mac,
-				    macaddr_t *gw_mac, void **arg_ptr);
+// Called once per send thread to initialize state.
+typedef int (*probe_thread_init_cb)(void **arg_ptr);
+
+// The make_packet callback is passed a buffer pointing at an ethernet header.
+// The buffer is MAX_PACKET_SIZE bytes. There are 1..n packet buffers in use
+// per send thread.  For each buffer, prepare_packet is called once before the
+// first call to make_packet.
+//
+// The probe module is expected to write all the constant packet contents
+// in prepare_packet, and only write the fields that need to be updated for
+// each packet being sent in make_packet.
+//
+typedef int (*probe_prepare_packet_cb)(void *packetbuf, macaddr_t *src_mac,
+				    macaddr_t *gw_mac, void *arg);
 
 // The make_packet callback is passed a buffer pointing at an ethernet header.
 // The buffer is MAX_PACKET_SIZE bytes. The callback must update the value
 // pointed at by buf_len with the actual length of the packet. The contents of
-// the buffer will match the previous packet sent. Every invocation of
-// make_packet contains a unique (src_ip, probe_num) tuple.
+// the buffer will match a previously sent packet by this send thread, so
+// content not overwritten by make_packet can be relied upon to be intact.
+// Beyond that, the probe module should not make any assumptions about buffers.
+// Every invocation of make_packet contains a unique (src_ip, probe_num) tuple.
 //
 // The probe module is responsible for populating the IP header. The src_ip,
 // dst_ip, and ttl are provided by the framework and must be set on the IP
@@ -84,6 +98,7 @@ typedef struct probe_module {
 
 	probe_global_init_cb global_initialize;
 	probe_thread_init_cb thread_initialize;
+	probe_prepare_packet_cb prepare_packet;
 	probe_make_packet_cb make_packet;
 	probe_print_packet_cb print_packet;
 	probe_validate_packet_cb validate_packet;
diff --git a/src/recv-netmap.c b/src/recv-netmap.c
index 3dba490a8..1b497e9e9 100644
--- a/src/recv-netmap.c
+++ b/src/recv-netmap.c
@@ -50,7 +50,6 @@ send_packet(make_packet_func_t mkpkt, void const *arg)
 	sock.nm.tx_ring_fd = zconf.nm.nm_fd;
 
 	batch_t *batch = create_packet_batch(1);
-	batch->packets[0].ip = 0; // unused by netmap
 	batch->packets[0].len = mkpkt(batch->packets[0].buf, arg);
 	assert(batch->packets[0].len <= MAX_PACKET_SIZE);
 	batch->len = 1;
@@ -67,7 +66,6 @@ static void
 submit_packet(make_packet_func_t mkpkt, void const *arg)
 {
 	batch_t *batch = create_packet_batch(1);
-	batch->packets[0].ip = 0; // unused by netmap
 	batch->packets[0].len = mkpkt(batch->packets[0].buf, arg);
 	assert(batch->packets[0].len <= MAX_PACKET_SIZE);
 	batch->len = 1;
diff --git a/src/send-bsd.c b/src/send-bsd.c
index af2631dce..4186f0e71 100644
--- a/src/send-bsd.c
+++ b/src/send-bsd.c
@@ -34,9 +34,10 @@ send_run_init(UNUSED sock_t sock)
 }
 
 static int
-send_packet(sock_t sock, void *buf, int len, UNUSED uint32_t retry_ct)
+send_packet(sock_t sock, uint8_t *buf, int len, UNUSED uint32_t retry_ct)
 {
 	if (zconf.send_ip_pkts) {
+		buf += sizeof(struct ether_header);
 		struct ip *iph = (struct ip *)buf;
 
 #if defined(__APPLE__) || (defined(__FreeBSD__) && __FreeBSD_version < 1100030)
@@ -95,12 +96,11 @@ send_batch(sock_t sock, batch_t* batch, int retries)
 		}
 		if (rc < 0) {
 			// packet couldn't be sent in retries number of attempts
-			struct in_addr addr;
-			addr.s_addr = batch->packets[packet_num].ip;
+			struct ip *iph = (struct ip *)(batch->packets[packet_num].buf + sizeof(struct ether_header));
 			char addr_str_buf[INET_ADDRSTRLEN];
 			const char *addr_str =
 			    inet_ntop(
-				AF_INET, &addr,
+				AF_INET, &iph->ip_dst,
 				addr_str_buf,
 				INET_ADDRSTRLEN);
 			if (addr_str != NULL) {
diff --git a/src/send-linux.c b/src/send-linux.c
index 1b502d0fa..def7c2199 100644
--- a/src/send-linux.c
+++ b/src/send-linux.c
@@ -75,10 +75,14 @@ int send_batch(sock_t sock, batch_t* batch, int retries) {
 	struct msghdr msgs[batch->capacity];
 	struct iovec iovs[batch->capacity];
 
+	size_t buf_offset = 0;
+	if (zconf.send_ip_pkts) {
+		buf_offset = sizeof(struct ether_header);
+	}
 	for (int i = 0; i < batch->len; ++i) {
 		struct iovec *iov = &iovs[i];
-		iov->iov_base = batch->packets[i].buf;
-		iov->iov_len = batch->packets[i].len;
+		iov->iov_base = batch->packets[i].buf + buf_offset;
+		iov->iov_len = batch->packets[i].len - buf_offset;
 		struct msghdr *msg = &msgs[i];
 		memset(msg, 0, sizeof(struct msghdr));
 		// based on https://github.com/torvalds/linux/blob/master/net/socket.c#L2180
@@ -87,7 +91,7 @@ int send_batch(sock_t sock, batch_t* batch, int retries) {
 		msg->msg_iov = iov;
 		msg->msg_iovlen = 1;
 		msgvec[i].msg_hdr = *msg;
-		msgvec[i].msg_len = batch->packets[i].len;
+		msgvec[i].msg_len = batch->packets[i].len - buf_offset;
 	}
 	// set up per-retry variables, so we can only re-submit what didn't send successfully
 	struct mmsghdr* current_msg_vec = msgvec;
diff --git a/src/send.c b/src/send.c
index 81cb106e2..f60022bdf 100644
--- a/src/send.c
+++ b/src/send.c
@@ -201,8 +201,6 @@ int send_run(sock_t st, shard_t *s)
 {
 	log_debug("send", "send thread started");
 	pthread_mutex_lock(&send_mutex);
-	// Allocate a buffer to hold the outgoing packet
-	char buf[MAX_PACKET_SIZE];
 	// allocate batch
 	batch_t* batch = create_packet_batch(zconf.batch);
 
@@ -211,6 +209,7 @@ int send_run(sock_t st, shard_t *s)
 		pthread_mutex_unlock(&send_mutex);
 		return EXIT_FAILURE;
 	}
+
 	// MAC address length in characters
 	char mac_buf[(ETHER_ADDR_LEN * 2) + (ETHER_ADDR_LEN - 1) + 1];
 	char *p = mac_buf;
@@ -224,13 +223,27 @@ int send_run(sock_t st, shard_t *s)
 		}
 	}
 	log_debug("send", "source MAC address %s", mac_buf);
-	void *probe_data;
+
+	void *probe_data = NULL;
 	if (zconf.probe_module->thread_initialize) {
-		zconf.probe_module->thread_initialize(
-		    buf, zconf.hw_mac, zconf.gw_mac, &probe_data);
+		int rv = zconf.probe_module->thread_initialize(&probe_data);
+		if (rv != EXIT_SUCCESS) {
+			pthread_mutex_unlock(&send_mutex);
+			log_fatal("send", "Send thread initialization for probe module failed: %u", rv);
+		}
 	}
 	pthread_mutex_unlock(&send_mutex);
 
+	if (zconf.probe_module->prepare_packet) {
+		for (size_t i = 0; i < batch->capacity; i++) {
+			int rv = zconf.probe_module->prepare_packet(
+					batch->packets[i].buf, zconf.hw_mac, zconf.gw_mac, probe_data);
+			if (rv != EXIT_SUCCESS) {
+				log_fatal("send", "Probe module failed to prepare packet: %u", rv);
+			}
+		}
+	}
+
 	// adaptive timing to hit target rate
 	uint64_t count = 0;
 	uint64_t last_count = count;
@@ -373,10 +386,11 @@ int send_run(sock_t st, shard_t *s)
 				     htons(current_port),
 				     (uint8_t *)validation);
 			uint8_t ttl = zconf.probe_ttl;
+
 			size_t length = 0;
 			zconf.probe_module->make_packet(
-			    buf, &length, src_ip, current_ip,
-			    htons(current_port), ttl, validation, i,
+			    batch->packets[batch->len].buf, &length,
+			    src_ip, current_ip, htons(current_port), ttl, validation, i,
 			    // Grab last 2 bytes of validation for ip_id
 			    (uint16_t)(validation[size_of_validation - 1] & 0xFFFF),
 			    probe_data);
@@ -387,25 +401,14 @@ int send_run(sock_t st, shard_t *s)
 				    s->thread_id, length,
 				    MAX_PACKET_SIZE);
 			}
+			batch->packets[batch->len].len = (uint32_t)length;
+
 			if (zconf.dryrun) {
 				lock_file(stdout);
 				zconf.probe_module->print_packet(stdout,
-								 buf);
+								 batch->packets[batch->len].buf);
 				unlock_file(stdout);
 			} else {
-				void *contents =
-				    buf +
-				    zconf.send_ip_pkts *
-					sizeof(struct ether_header);
-				length -= (zconf.send_ip_pkts *
-					   sizeof(struct ether_header));
-				// add packet to batch and update metadata
-				// this is an additional memcpy (packet created in buf, buf -> batch)
-				// but when I modified the TCP SYN module to write packet to batch directly, there wasn't any noticeable speedup.
-				// Using this approach for readability/minimal changes
-				batch->packets[batch->len].ip = current_ip;
-				batch->packets[batch->len].len = length;
-				memcpy(batch->packets[batch->len].buf, contents, length);
 				batch->len++;
 				if (batch->len == batch->capacity) {
 					// batch is full, sending
diff --git a/src/send.h b/src/send.h
index 430d500f8..39b3cb437 100644
--- a/src/send.h
+++ b/src/send.h
@@ -12,22 +12,32 @@
 #include "iterator.h"
 #include "socket.h"
 
+#include <assert.h>
+
 iterator_t *send_init(void);
 int send_run(sock_t, shard_t *);
 
 // Fit two packets with metadata into one 4k page.
 // 2k seems like more than enough with typical MTU of
 // 1500, and we don't want to cause IP fragmentation.
-#define MAX_PACKET_SIZE (2048 - 2 * sizeof(uint32_t))
+#define MAX_PACKET_SIZE (2048 - sizeof(uint32_t) - 2 * sizeof(uint8_t))
 
 // Metadata and initial packet bytes are adjacent,
 // for cache locality esp. with short packets.
+// buf is aligned such that the end of the Ethernet
+// header and beginning of the IP header will align
+// to a 32 bit boundary, such that reading/writing
+// IP addresses and other 32 bit header fields is
+// properly aligned.
 struct batch_packet {
-	uint32_t ip;
 	uint32_t len;
+	uint8_t unused[2];
 	uint8_t buf[MAX_PACKET_SIZE];
 };
 
+static_assert((offsetof(struct batch_packet, buf) + sizeof(struct ether_header)) % sizeof(uint32_t) == 0,
+	      "buf is aligned such that IP header is 32-bit aligned");
+
 typedef struct {
 	struct batch_packet *packets;
 	uint16_t len;