[PATCH 0/3] BOOTP/DHCPv4 enhancements

[PATCH 0/3] BOOTP/DHCPv4 enhancements

[seanedmond]

From: Sean Edmond <seanedmond@microsoft.com>

In our datacenter application, a single DHCP server is servicing 36000+ clients.
Improvements are required to the DHCPv4 retransmission behavior to align with
RFC and ensure less pressure is exerted on the server:
- retransmission backoff interval maximum is configurable 
  (environment variable bootpretransmitperiodmax)
- initial retransmission backoff interval is configurable 
  (environment variable bootpretransmitperiodinit)
- transaction ID is kept the same for each BOOTP/DHCPv4 request 
  (not recreated on each retry)

For our application we'll use:
- bootpretransmitperiodmax=16000
- bootpretransmitperiodinit=2000

A new configuration BOOTP_RANDOM_XID has been added to enable a randomized
BOOTP/DHCPv4 transaction ID.

Add functionality for DHCPv4 sending/parsing option 209 (PXE config file).
Enabled with Kconfig BOOTP_PXE_DHCP_OPTION.  Note, this patch was
submitted previously but this latest version has been enhanced to
avoid a possible double free().

Sean Edmond (3):
  net: Get pxe config file from dhcp option 209
  net: bootp: BOOTP/DHCPv4 retransmission improvements
  net: bootp: add config option BOOTP_RANDOM_XID

 cmd/Kconfig | 11 +++++++
 cmd/pxe.c   | 10 +++++++
 net/bootp.c | 85 +++++++++++++++++++++++++++++++++++++++++++----------
 3 files changed, 91 insertions(+), 15 deletions(-)

-- 
2.40.0

[PATCH 1/3] net: Get pxe config file from dhcp option 209

[seanedmond]

From: Sean Edmond <seanedmond@microsoft.com>

Allow dhcp server pass pxe config file full path by using option 209

Signed-off-by: Sean Edmond <seanedmond@microsoft.com>
---
 cmd/Kconfig |  4 ++++
 cmd/pxe.c   | 10 ++++++++++
 net/bootp.c | 21 +++++++++++++++++++++
 3 files changed, 35 insertions(+)

diff --git a/cmd/Kconfig b/cmd/Kconfig
index 43ca10f69c..25c1efc41e 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -1817,6 +1817,10 @@ config BOOTP_PXE_CLIENTARCH
 	default 0x15 if ARM
 	default 0 if X86
 
+config BOOTP_PXE_DHCP_OPTION
+	bool "Request & store 'pxe_configfile' from BOOTP/DHCP server"
+	depends on BOOTP_PXE
+
 config BOOTP_VCI_STRING
 	string
 	depends on CMD_BOOTP
diff --git a/cmd/pxe.c b/cmd/pxe.c
index 677142520b..83c4ed5411 100644
--- a/cmd/pxe.c
+++ b/cmd/pxe.c
@@ -65,6 +65,8 @@ static int pxe_dhcp_option_path(struct pxe_context *ctx, unsigned long pxefile_a
 	int ret = get_pxe_file(ctx, pxelinux_configfile, pxefile_addr_r);
 
 	free(pxelinux_configfile);
+	/* set to NULL to avoid double-free if DHCP is tried again */
+	pxelinux_configfile = NULL;
 
 	return ret;
 }
@@ -141,6 +143,14 @@ int pxe_get(ulong pxefile_addr_r, char **bootdirp, ulong *sizep, bool use_ipv6)
 			  env_get("bootfile"), use_ipv6))
 		return -ENOMEM;
 
+	if (IS_ENABLED(CONFIG_BOOTP_PXE_DHCP_OPTION) &&
+	    pxelinux_configfile && !use_ipv6) {
+		if (pxe_dhcp_option_path(&ctx, pxefile_addr_r) > 0)
+			goto done;
+
+		goto error_exit;
+	}
+
 	if (IS_ENABLED(CONFIG_DHCP6_PXE_DHCP_OPTION) &&
 	    pxelinux_configfile && use_ipv6) {
 		if (pxe_dhcp_option_path(&ctx, pxefile_addr_r) > 0)
diff --git a/net/bootp.c b/net/bootp.c
index 8b1a4ae2ef..013d54c7ed 100644
--- a/net/bootp.c
+++ b/net/bootp.c
@@ -26,6 +26,7 @@
 #ifdef CONFIG_BOOTP_RANDOM_DELAY
 #include "net_rand.h"
 #endif
+#include <malloc.h>
 
 #define BOOTP_VENDOR_MAGIC	0x63825363	/* RFC1048 Magic Cookie */
 
@@ -604,6 +605,10 @@ static int dhcp_extended(u8 *e, int message_type, struct in_addr server_ip,
 	*e++  = 42;
 	*cnt += 1;
 #endif
+	if (IS_ENABLED(CONFIG_BOOTP_PXE_DHCP_OPTION)) {
+		*e++ = 209;	/* PXELINUX Config File */
+		*cnt += 1;
+	}
 	/* no options, so back up to avoid sending an empty request list */
 	if (*cnt == 0)
 		e -= 2;
@@ -912,6 +917,22 @@ static void dhcp_process_options(uchar *popt, uchar *end)
 				net_boot_file_name[size] = 0;
 			}
 			break;
+		case 209:	/* PXELINUX Config File */
+			if (IS_ENABLED(CONFIG_BOOTP_PXE_DHCP_OPTION)) {
+				/* In case it has already been allocated when get DHCP Offer packet,
+				 * free first to avoid memory leak.
+				 */
+				if (pxelinux_configfile)
+					free(pxelinux_configfile);
+
+				pxelinux_configfile = (char *)malloc((oplen + 1) * sizeof(char));
+
+				if (pxelinux_configfile)
+					strlcpy(pxelinux_configfile, popt + 2, oplen + 1);
+				else
+					printf("Error: Failed to allocate pxelinux_configfile\n");
+			}
+			break;
 		default:
 #if defined(CONFIG_BOOTP_VENDOREX)
 			if (dhcp_vendorex_proc(popt))
-- 
2.40.0

[PATCH 2/3] net: bootp: BOOTP/DHCPv4 retransmission improvements

[seanedmond]

From: Sean Edmond <seanedmond@microsoft.com>

This patch introduces 3 improvements to align with RFC 951:
- retransmission backoff interval maximum is configurable
- initial retranmission backoff interval is configurable
- transaction ID is kept the same for each BOOTP/DHCPv4 request

In applications where thousands of nodes are serviced by a single DHCP
server, maximizing the retransmission backoff interval at 2 seconds (the
current u-boot default) exerts high pressure on the DHCP server and
network layer.

RFC 951 “7.2. Client Retransmission Strategy” states that the
retransmission backoff interval should maximize at 60 seconds.  This
patch allows the interval to be configurable using the environment
variable "bootpretransmitperiodmax"

The initial retranmission backoff period defaults to 250ms, which is
also too small for these scenarios with many clients.  This patch makes
the initial retransmission interval to be configurable using the
environment variable "bootpretransmitperiodinit".

Also, on a retransmission it is not expected for the transaction ID to
change (only the 'secs' field should be updated). Let's save the
transaction ID and use the same transaction ID for each BOOTP/DHCPv4
exchange.

Signed-off-by: Sean Edmond <seanedmond@microsoft.com>
---
 net/bootp.c | 63 +++++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 47 insertions(+), 16 deletions(-)

diff --git a/net/bootp.c b/net/bootp.c
index 013d54c7ed..7248536cc4 100644
--- a/net/bootp.c
+++ b/net/bootp.c
@@ -42,6 +42,17 @@
  */
 #define TIMEOUT_MS	((3 + (CONFIG_NET_RETRY_COUNT * 5)) * 1000)
 
+/*
+ * According to rfc951 : 7.2. Client Retransmission Strategy
+ * "After the 'average' backoff reaches about 60 seconds, it should be
+ * increased no further, but still randomized."
+ *
+ * U-Boot has saturated this backoff at 2 seconds for a long time.
+ * To modify, set the environment variable "bootpretransmitperiodmax"
+ */
+#define RETRANSMIT_PERIOD_MAX_MS	2000
+#define RETRANSMIT_PERIOD_INIT_MS	250
+
 #define PORT_BOOTPS	67		/* BOOTP server UDP port */
 #define PORT_BOOTPC	68		/* BOOTP client UDP port */
 
@@ -56,6 +67,7 @@
 u32		bootp_ids[CFG_BOOTP_ID_CACHE_SIZE];
 unsigned int	bootp_num_ids;
 int		bootp_try;
+u32		bootp_id;
 ulong		bootp_start;
 ulong		bootp_timeout;
 char net_nis_domain[32] = {0,}; /* Our NIS domain */
@@ -63,6 +75,7 @@ char net_hostname[32] = {0,}; /* Our hostname */
 char net_root_path[CONFIG_BOOTP_MAX_ROOT_PATH_LEN] = {0,}; /* Our bootpath */
 
 static ulong time_taken_max;
+static u32   retransmit_period_max_ms;
 
 #if defined(CONFIG_CMD_DHCP)
 static dhcp_state_t dhcp_state = INIT;
@@ -417,8 +430,8 @@ static void bootp_timeout_handler(void)
 		}
 	} else {
 		bootp_timeout *= 2;
-		if (bootp_timeout > 2000)
-			bootp_timeout = 2000;
+		if (bootp_timeout > retransmit_period_max_ms)
+			bootp_timeout = retransmit_period_max_ms;
 		net_set_timeout_handler(bootp_timeout, bootp_timeout_handler);
 		bootp_request();
 	}
@@ -714,10 +727,18 @@ static int bootp_extended(u8 *e)
 
 void bootp_reset(void)
 {
+	char *ep;  /* Environment pointer */
+
 	bootp_num_ids = 0;
 	bootp_try = 0;
 	bootp_start = get_timer(0);
-	bootp_timeout = 250;
+
+	ep = env_get("bootpretransmitperiodinit");
+	if (ep)
+		bootp_timeout = dectoul(ep, NULL);
+	else
+		bootp_timeout = RETRANSMIT_PERIOD_INIT_MS;
+
 }
 
 void bootp_request(void)
@@ -729,7 +750,6 @@ void bootp_request(void)
 #ifdef CONFIG_BOOTP_RANDOM_DELAY
 	ulong rand_ms;
 #endif
-	u32 bootp_id;
 	struct in_addr zero_ip;
 	struct in_addr bcast_ip;
 	char *ep;  /* Environment pointer */
@@ -745,6 +765,12 @@ void bootp_request(void)
 	else
 		time_taken_max = TIMEOUT_MS;
 
+	ep = env_get("bootpretransmitperiodmax");
+	if (ep)
+		retransmit_period_max_ms = dectoul(ep, NULL);
+	else
+		retransmit_period_max_ms = RETRANSMIT_PERIOD_MAX_MS;
+
 #ifdef CONFIG_BOOTP_RANDOM_DELAY		/* Random BOOTP delay */
 	if (bootp_try == 0)
 		srand_mac();
@@ -804,18 +830,23 @@ void bootp_request(void)
 	extlen = bootp_extended((u8 *)bp->bp_vend);
 #endif
 
-	/*
-	 *	Bootp ID is the lower 4 bytes of our ethernet address
-	 *	plus the current time in ms.
-	 */
-	bootp_id = ((u32)net_ethaddr[2] << 24)
-		| ((u32)net_ethaddr[3] << 16)
-		| ((u32)net_ethaddr[4] << 8)
-		| (u32)net_ethaddr[5];
-	bootp_id += get_timer(0);
-	bootp_id = htonl(bootp_id);
-	bootp_add_id(bootp_id);
-	net_copy_u32(&bp->bp_id, &bootp_id);
+	/* Only generate a new transaction ID for each new BOOTP request */
+	if (bootp_try == 1) {
+		/*
+		 *	Bootp ID is the lower 4 bytes of our ethernet address
+		 *	plus the current time in ms.
+		 */
+		bootp_id = ((u32)net_ethaddr[2] << 24)
+			| ((u32)net_ethaddr[3] << 16)
+			| ((u32)net_ethaddr[4] << 8)
+			| (u32)net_ethaddr[5];
+		bootp_id += get_timer(0);
+		bootp_id = htonl(bootp_id);
+		bootp_add_id(bootp_id);
+		net_copy_u32(&bp->bp_id, &bootp_id);
+	} else {
+		net_copy_u32(&bp->bp_id, &bootp_id);
+	}
 
 	/*
 	 * Calculate proper packet lengths taking into account the
-- 
2.40.0

Re: [PATCH 2/3] net: bootp: BOOTP/DHCPv4 retransmission improvements

[Lothar Waßmann]

Hi,

On Mon, 25 Sep 2023 13:29:34 -0700 seanedmond@linux.microsoft.com wrote:
> From: Sean Edmond <seanedmond@microsoft.com>
> 
> This patch introduces 3 improvements to align with RFC 951:
> - retransmission backoff interval maximum is configurable
> - initial retranmission backoff interval is configurable
> - transaction ID is kept the same for each BOOTP/DHCPv4 request
> 
> In applications where thousands of nodes are serviced by a single DHCP
> server, maximizing the retransmission backoff interval at 2 seconds (the
> current u-boot default) exerts high pressure on the DHCP server and
> network layer.
> 
> RFC 951 “7.2. Client Retransmission Strategy” states that the
> retransmission backoff interval should maximize at 60 seconds.  This
> patch allows the interval to be configurable using the environment
> variable "bootpretransmitperiodmax"
> 
> The initial retranmission backoff period defaults to 250ms, which is
> also too small for these scenarios with many clients.  This patch makes
> the initial retransmission interval to be configurable using the
> environment variable "bootpretransmitperiodinit".
> 
> Also, on a retransmission it is not expected for the transaction ID to
> change (only the 'secs' field should be updated). Let's save the
> transaction ID and use the same transaction ID for each BOOTP/DHCPv4
> exchange.
> 
> Signed-off-by: Sean Edmond <seanedmond@microsoft.com>
> ---
>  net/bootp.c | 63 +++++++++++++++++++++++++++++++++++++++--------------
>  1 file changed, 47 insertions(+), 16 deletions(-)
> 
> diff --git a/net/bootp.c b/net/bootp.c
> index 013d54c7ed..7248536cc4 100644
> --- a/net/bootp.c
> +++ b/net/bootp.c
> @@ -42,6 +42,17 @@
>   */
>  #define TIMEOUT_MS	((3 + (CONFIG_NET_RETRY_COUNT * 5)) * 1000)
>  
> +/*
> + * According to rfc951 : 7.2. Client Retransmission Strategy
> + * "After the 'average' backoff reaches about 60 seconds, it should be
> + * increased no further, but still randomized."
> + *
> + * U-Boot has saturated this backoff at 2 seconds for a long time.
> + * To modify, set the environment variable "bootpretransmitperiodmax"
> + */
> +#define RETRANSMIT_PERIOD_MAX_MS	2000
> +#define RETRANSMIT_PERIOD_INIT_MS	250
> +
>  #define PORT_BOOTPS	67		/* BOOTP server UDP port */
>  #define PORT_BOOTPC	68		/* BOOTP client UDP port */
>  
> @@ -56,6 +67,7 @@
>  u32		bootp_ids[CFG_BOOTP_ID_CACHE_SIZE];
>  unsigned int	bootp_num_ids;
>  int		bootp_try;
> +u32		bootp_id;
>  ulong		bootp_start;
>  ulong		bootp_timeout;
>  char net_nis_domain[32] = {0,}; /* Our NIS domain */
> @@ -63,6 +75,7 @@ char net_hostname[32] = {0,}; /* Our hostname */
>  char net_root_path[CONFIG_BOOTP_MAX_ROOT_PATH_LEN] = {0,}; /* Our bootpath */
>  
>  static ulong time_taken_max;
> +static u32   retransmit_period_max_ms;
>  
>  #if defined(CONFIG_CMD_DHCP)
>  static dhcp_state_t dhcp_state = INIT;
> @@ -417,8 +430,8 @@ static void bootp_timeout_handler(void)
>  		}
>  	} else {
>  		bootp_timeout *= 2;
> -		if (bootp_timeout > 2000)
> -			bootp_timeout = 2000;
> +		if (bootp_timeout > retransmit_period_max_ms)
> +			bootp_timeout = retransmit_period_max_ms;
>  		net_set_timeout_handler(bootp_timeout, bootp_timeout_handler);
>  		bootp_request();
>  	}
> @@ -714,10 +727,18 @@ static int bootp_extended(u8 *e)
>  
>  void bootp_reset(void)
>  {
> +	char *ep;  /* Environment pointer */
> +
>  	bootp_num_ids = 0;
>  	bootp_try = 0;
>  	bootp_start = get_timer(0);
> -	bootp_timeout = 250;
> +
> +	ep = env_get("bootpretransmitperiodinit");
> +	if (ep)
> +		bootp_timeout = dectoul(ep, NULL);
> +	else
> +		bootp_timeout = RETRANSMIT_PERIOD_INIT_MS;
> +
bootp_timeout = env_get_ulong("bootpretransmitperiodinit", 0, RETRANSMIT_PERIOD_INIT_MS);
does the same...

>  }
>  
>  void bootp_request(void)
> @@ -729,7 +750,6 @@ void bootp_request(void)
>  #ifdef CONFIG_BOOTP_RANDOM_DELAY
>  	ulong rand_ms;
>  #endif
> -	u32 bootp_id;
>  	struct in_addr zero_ip;
>  	struct in_addr bcast_ip;
>  	char *ep;  /* Environment pointer */
> @@ -745,6 +765,12 @@ void bootp_request(void)
>  	else
>  		time_taken_max = TIMEOUT_MS;
>  
> +	ep = env_get("bootpretransmitperiodmax");
> +	if (ep)
> +		retransmit_period_max_ms = dectoul(ep, NULL);
> +	else
> +		retransmit_period_max_ms = RETRANSMIT_PERIOD_MAX_MS;
> +
see above


Lothar Waßmann

Re: [PATCH 2/3] net: bootp: BOOTP/DHCPv4 retransmission improvements

[Sean Edmond]

On 2023-09-26 9:11 p.m., Lothar Waßmann wrote:
> Hi,
>
> On Mon, 25 Sep 2023 13:29:34 -0700 seanedmond@linux.microsoft.com wrote:
>> From: Sean Edmond <seanedmond@microsoft.com>
>>
>> This patch introduces 3 improvements to align with RFC 951:
>> - retransmission backoff interval maximum is configurable
>> - initial retranmission backoff interval is configurable
>> - transaction ID is kept the same for each BOOTP/DHCPv4 request
>>
>> In applications where thousands of nodes are serviced by a single DHCP
>> server, maximizing the retransmission backoff interval at 2 seconds (the
>> current u-boot default) exerts high pressure on the DHCP server and
>> network layer.
>>
>> RFC 951 “7.2. Client Retransmission Strategy” states that the
>> retransmission backoff interval should maximize at 60 seconds.  This
>> patch allows the interval to be configurable using the environment
>> variable "bootpretransmitperiodmax"
>>
>> The initial retranmission backoff period defaults to 250ms, which is
>> also too small for these scenarios with many clients.  This patch makes
>> the initial retransmission interval to be configurable using the
>> environment variable "bootpretransmitperiodinit".
>>
>> Also, on a retransmission it is not expected for the transaction ID to
>> change (only the 'secs' field should be updated). Let's save the
>> transaction ID and use the same transaction ID for each BOOTP/DHCPv4
>> exchange.
>>
>> Signed-off-by: Sean Edmond <seanedmond@microsoft.com>
>> ---
>>   net/bootp.c | 63 +++++++++++++++++++++++++++++++++++++++--------------
>>   1 file changed, 47 insertions(+), 16 deletions(-)
>>
>> diff --git a/net/bootp.c b/net/bootp.c
>> index 013d54c7ed..7248536cc4 100644
>> --- a/net/bootp.c
>> +++ b/net/bootp.c
>> @@ -42,6 +42,17 @@
>>    */
>>   #define TIMEOUT_MS	((3 + (CONFIG_NET_RETRY_COUNT * 5)) * 1000)
>>   
>> +/*
>> + * According to rfc951 : 7.2. Client Retransmission Strategy
>> + * "After the 'average' backoff reaches about 60 seconds, it should be
>> + * increased no further, but still randomized."
>> + *
>> + * U-Boot has saturated this backoff at 2 seconds for a long time.
>> + * To modify, set the environment variable "bootpretransmitperiodmax"
>> + */
>> +#define RETRANSMIT_PERIOD_MAX_MS	2000
>> +#define RETRANSMIT_PERIOD_INIT_MS	250
>> +
>>   #define PORT_BOOTPS	67		/* BOOTP server UDP port */
>>   #define PORT_BOOTPC	68		/* BOOTP client UDP port */
>>   
>> @@ -56,6 +67,7 @@
>>   u32		bootp_ids[CFG_BOOTP_ID_CACHE_SIZE];
>>   unsigned int	bootp_num_ids;
>>   int		bootp_try;
>> +u32		bootp_id;
>>   ulong		bootp_start;
>>   ulong		bootp_timeout;
>>   char net_nis_domain[32] = {0,}; /* Our NIS domain */
>> @@ -63,6 +75,7 @@ char net_hostname[32] = {0,}; /* Our hostname */
>>   char net_root_path[CONFIG_BOOTP_MAX_ROOT_PATH_LEN] = {0,}; /* Our bootpath */
>>   
>>   static ulong time_taken_max;
>> +static u32   retransmit_period_max_ms;
>>   
>>   #if defined(CONFIG_CMD_DHCP)
>>   static dhcp_state_t dhcp_state = INIT;
>> @@ -417,8 +430,8 @@ static void bootp_timeout_handler(void)
>>   		}
>>   	} else {
>>   		bootp_timeout *= 2;
>> -		if (bootp_timeout > 2000)
>> -			bootp_timeout = 2000;
>> +		if (bootp_timeout > retransmit_period_max_ms)
>> +			bootp_timeout = retransmit_period_max_ms;
>>   		net_set_timeout_handler(bootp_timeout, bootp_timeout_handler);
>>   		bootp_request();
>>   	}
>> @@ -714,10 +727,18 @@ static int bootp_extended(u8 *e)
>>   
>>   void bootp_reset(void)
>>   {
>> +	char *ep;  /* Environment pointer */
>> +
>>   	bootp_num_ids = 0;
>>   	bootp_try = 0;
>>   	bootp_start = get_timer(0);
>> -	bootp_timeout = 250;
>> +
>> +	ep = env_get("bootpretransmitperiodinit");
>> +	if (ep)
>> +		bootp_timeout = dectoul(ep, NULL);
>> +	else
>> +		bootp_timeout = RETRANSMIT_PERIOD_INIT_MS;
>> +
> bootp_timeout = env_get_ulong("bootpretransmitperiodinit", 0, RETRANSMIT_PERIOD_INIT_MS);
> does the same...
Thanks for the suggestion, will fix in v2.
>>   }
>>   
>>   void bootp_request(void)
>> @@ -729,7 +750,6 @@ void bootp_request(void)
>>   #ifdef CONFIG_BOOTP_RANDOM_DELAY
>>   	ulong rand_ms;
>>   #endif
>> -	u32 bootp_id;
>>   	struct in_addr zero_ip;
>>   	struct in_addr bcast_ip;
>>   	char *ep;  /* Environment pointer */
>> @@ -745,6 +765,12 @@ void bootp_request(void)
>>   	else
>>   		time_taken_max = TIMEOUT_MS;
>>   
>> +	ep = env_get("bootpretransmitperiodmax");
>> +	if (ep)
>> +		retransmit_period_max_ms = dectoul(ep, NULL);
>> +	else
>> +		retransmit_period_max_ms = RETRANSMIT_PERIOD_MAX_MS;
>> +
> see above
>
>
> Lothar Waßmann

[PATCH 3/3] net: bootp: add config option BOOTP_RANDOM_XID

[seanedmond]

From: Sean Edmond <seanedmond@microsoft.com>

The new config option BOOTP_RANDOM_XID will randomize the transaction ID
for each new BOOT/DHCPv4 exchange.

Signed-off-by: Sean Edmond <seanedmond@microsoft.com>
---
 cmd/Kconfig |  7 +++++++
 net/bootp.c | 31 +++++++++++++++++--------------
 2 files changed, 24 insertions(+), 14 deletions(-)

diff --git a/cmd/Kconfig b/cmd/Kconfig
index 25c1efc41e..4be5be8724 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -1829,6 +1829,13 @@ config BOOTP_VCI_STRING
 	default "U-Boot.arm" if ARM
 	default "U-Boot"
 
+config BOOTP_RANDOM_XID
+	bool "Send random transaction ID to BOOTP/DHCP server"
+	depends on CMD_BOOTP
+	help
+	  Selecting this will allow for a random transaction ID to get
+	  selected for each BOOTP/DHCPv4 exchange.
+
 if CMD_DHCP6
 
 config DHCP6_PXE_CLIENTARCH
diff --git a/net/bootp.c b/net/bootp.c
index 7248536cc4..5053a1b870 100644
--- a/net/bootp.c
+++ b/net/bootp.c
@@ -832,22 +832,25 @@ void bootp_request(void)
 
 	/* Only generate a new transaction ID for each new BOOTP request */
 	if (bootp_try == 1) {
-		/*
-		 *	Bootp ID is the lower 4 bytes of our ethernet address
-		 *	plus the current time in ms.
-		 */
-		bootp_id = ((u32)net_ethaddr[2] << 24)
-			| ((u32)net_ethaddr[3] << 16)
-			| ((u32)net_ethaddr[4] << 8)
-			| (u32)net_ethaddr[5];
-		bootp_id += get_timer(0);
-		bootp_id = htonl(bootp_id);
-		bootp_add_id(bootp_id);
-		net_copy_u32(&bp->bp_id, &bootp_id);
-	} else {
-		net_copy_u32(&bp->bp_id, &bootp_id);
+		if (IS_ENABLED(CONFIG_BOOTP_RANDOM_XID)) {
+			srand(get_ticks() + rand());
+			bootp_id = rand();
+		} else {
+			/*
+			 *	Bootp ID is the lower 4 bytes of our ethernet address
+			 *	plus the current time in ms.
+			 */
+			bootp_id = ((u32)net_ethaddr[2] << 24)
+				| ((u32)net_ethaddr[3] << 16)
+				| ((u32)net_ethaddr[4] << 8)
+				| (u32)net_ethaddr[5];
+			bootp_id += get_timer(0);
+			bootp_id = htonl(bootp_id);
+		}
 	}
 
+	bootp_add_id(bootp_id);
+	net_copy_u32(&bp->bp_id, &bootp_id);
 	/*
 	 * Calculate proper packet lengths taking into account the
 	 * variable size of the options field
-- 
2.40.0

Re: [PATCH 0/3] BOOTP/DHCPv4 enhancements

[Peter Robinson]

Hi Sean,

> In our datacenter application, a single DHCP server is servicing 36000+ clients.
> Improvements are required to the DHCPv4 retransmission behavior to align with
> RFC and ensure less pressure is exerted on the server:
> - retransmission backoff interval maximum is configurable
>   (environment variable bootpretransmitperiodmax)
> - initial retransmission backoff interval is configurable
>   (environment variable bootpretransmitperiodinit)
> - transaction ID is kept the same for each BOOTP/DHCPv4 request
>   (not recreated on each retry)

Might be also worth looking at the series adding LWIP support [1] and
see what impact that may have on this too.

Peter

[1] https://lists.denx.de/pipermail/u-boot/2023-September/531716.html

> For our application we'll use:
> - bootpretransmitperiodmax=16000
> - bootpretransmitperiodinit=2000
>
> A new configuration BOOTP_RANDOM_XID has been added to enable a randomized
> BOOTP/DHCPv4 transaction ID.
>
> Add functionality for DHCPv4 sending/parsing option 209 (PXE config file).
> Enabled with Kconfig BOOTP_PXE_DHCP_OPTION.  Note, this patch was
> submitted previously but this latest version has been enhanced to
> avoid a possible double free().
>
> Sean Edmond (3):
>   net: Get pxe config file from dhcp option 209
>   net: bootp: BOOTP/DHCPv4 retransmission improvements
>   net: bootp: add config option BOOTP_RANDOM_XID
>
>  cmd/Kconfig | 11 +++++++
>  cmd/pxe.c   | 10 +++++++
>  net/bootp.c | 85 +++++++++++++++++++++++++++++++++++++++++++----------
>  3 files changed, 91 insertions(+), 15 deletions(-)
>
> --
> 2.40.0
>

Re: [PATCH 0/3] BOOTP/DHCPv4 enhancements

[Sean Edmond]

On 2023-09-26 9:45 a.m., Peter Robinson wrote:
> Hi Sean,
>
>> In our datacenter application, a single DHCP server is servicing 36000+ clients.
>> Improvements are required to the DHCPv4 retransmission behavior to align with
>> RFC and ensure less pressure is exerted on the server:
>> - retransmission backoff interval maximum is configurable
>>    (environment variable bootpretransmitperiodmax)
>> - initial retransmission backoff interval is configurable
>>    (environment variable bootpretransmitperiodinit)
>> - transaction ID is kept the same for each BOOTP/DHCPv4 request
>>    (not recreated on each retry)
> Might be also worth looking at the series adding LWIP support [1] and
> see what impact that may have on this too.
>
> Peter
>
> [1]https://lists.denx.de/pipermail/u-boot/2023-September/531716.html

I'm aware of the LWIP addition but haven't made any attempt to 
characterize the retransmission behavior.

My understanding is that LWIP doesn't support DHCPv6 or TFTP with IPv6 
yet.  Our preference would be to stick with the u-boot networking stack 
for now until LWIP adds full support for IPv6.

Given the importance of the retransmission behavior is for our use-case 
(36000+ clients pers server), we would have to qualify/validate LWIP 
before transitioning.



>> For our application we'll use:
>> - bootpretransmitperiodmax=16000
>> - bootpretransmitperiodinit=2000
>>
>> A new configuration BOOTP_RANDOM_XID has been added to enable a randomized
>> BOOTP/DHCPv4 transaction ID.
>>
>> Add functionality for DHCPv4 sending/parsing option 209 (PXE config file).
>> Enabled with Kconfig BOOTP_PXE_DHCP_OPTION.  Note, this patch was
>> submitted previously but this latest version has been enhanced to
>> avoid a possible double free().
>>
>> Sean Edmond (3):
>>    net: Get pxe config file from dhcp option 209
>>    net: bootp: BOOTP/DHCPv4 retransmission improvements
>>    net: bootp: add config option BOOTP_RANDOM_XID
>>
>>   cmd/Kconfig | 11 +++++++
>>   cmd/pxe.c   | 10 +++++++
>>   net/bootp.c | 85 +++++++++++++++++++++++++++++++++++++++++++----------
>>   3 files changed, 91 insertions(+), 15 deletions(-)
>>
>> --
>> 2.40.0
>>