The maximum send length for UDP is the maximum size of a UDP datagram.

For UDP over IPv4, this is the maximum IPv4 packet size (65535) minus
the size of the IPv4 and UDP headers, arriving at 65507.

In theory for a system implementing IPv6 jumbogram support, there is
no maximum packet size for UDP.  In practice we've observed with
CentOS 5 a limitation of 65535 - 8, which is dictated by the size
field in the UDP header (it has a maximum value of 65535, but needs
to count both payload and header bytes, thus subtracting off the 8
bytes for the UDP header).

We take the most conservative approach and use the 65507 value
for UDP / IPv4.

This is (I believe) the last part of issue #212.

src/iperf.h

@@ -291,6 +291,8 @@ struct iperf_test
 #define MB (1024 * 1024)
 #define MAX_TCP_BUFFER (512 * MB)
 #define MAX_BLOCKSIZE MB
+/* Maximum size UDP send is (64K - 1) - IP and UDP header sizes */
+#define MAX_UDP_BLOCKSIZE (65535 - 8 - 20)
 #define MIN_INTERVAL 0.1
 #define MAX_INTERVAL 60.0
 #define MAX_TIME 86400

src/iperf_api.c

@@ -913,6 +913,11 @@ iperf_parse_arguments(struct iperf_test *test, int argc, char **argv)
 	i_errno = IEBLOCKSIZE;
 	return -1;
     }
+    if (test->protocol->id == Pudp &&
+	blksize > MAX_UDP_BLOCKSIZE) {
+	i_errno = IEUDPBLOCKSIZE;
+	return -1;
+    }
     test->settings->blksize = blksize;
 
     if (!rate_flag)

src/iperf_api.h

@@ -281,6 +281,7 @@ enum {
     IELOGFILE = 17,	    // Can't open log file
     IENOSCTP = 18,	    // No SCTP support available
     IEBIND = 19,			// Local port specified with no local bind option
+    IEUDPBLOCKSIZE = 20,    // Block size too large. Maximum value = %dMAX_UDP_BLOCKSIZE
     /* Test errors */
     IENEWTEST = 100,        // Unable to create a new test (check perror)
     IEINITTEST = 101,       // Test initialization failed (check perror)

src/iperf_error.c

@@ -124,6 +124,9 @@ iperf_strerror(int i_errno)
         case IEBIND:
             snprintf(errstr, len, "--bind must be specified to use --cport");
             break;
+        case IEUDPBLOCKSIZE:
+            snprintf(errstr, len, "block size too large (maximum = %d bytes)", MAX_UDP_BLOCKSIZE);
+            break;
         case IEMSS:
             snprintf(errstr, len, "TCP MSS too large (maximum = %d bytes)", MAX_MSS);
             break;