Date: Wed, 14 Mar 2001 09:15:49 -0800 From: Lars Eggert <larse@ISI.EDU> To: David Malone <dwmalone@maths.tcd.ie> Cc: freebsd-net@freebsd.org Subject: Re: UDP datagram max size. Message-ID: <3AAFA745.AA3EC6B6@isi.edu> References: <200103141703.aa78458@salmon.maths.tcd.ie>
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This is a cryptographically signed message in MIME format. --------------ms0617D6FE6914F636D4A0402D Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit David Malone wrote: > > I'm trying to figure out what #define I should use for the largest > UDP datagram. The header files don't seem to define a constant for > this. The correct size would seem to be 65535 'cos there are two > bytes in the UDP header for the size. > > IP_MAXPACKET and IPV6_MAXPACKET are available and have the right > values, but these don't really seem to be the correct thing to use > 'cos they don't take headers or the possibility Jumbo payload into > account. To support jumbograms, I don't think you'll get around dynamic memory allocation. (There is no reasonable upper bound for the buffer size.) However, RFC2675 says: The Jumbo Payload option is relevant only for IPv6 nodes that may be attached to links with a link MTU greater than 65,575 octets (that is, 65,535 + 40, where 40 octets is the size of the IPv6 header). The Jumbo Payload option need not be implemented or understood by IPv6 nodes that do not support attachment to links with MTU greater than 65,575. So it may be okay to punt on jumbograms for now, and use a 64K static buffer like the patch in the PR does. Even if you do implement support for jumbograms, I think keeping the 64K static buffer around as a "fast-path" for the common case makes sense. > I wanted to commit something for: > > http://www.FreeBSD.org/cgi/query-pr.cgi?pr=25050 > > but I'm not convinced that the patch is spot on. I could determine > the data size and malloc memory dynamically I guess. -- Lars Eggert <larse@isi.edu> Information Sciences Institute http://www.isi.edu/larse/ University of Southern California --------------ms0617D6FE6914F636D4A0402D Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="smime.p7s" Content-Description: S/MIME Cryptographic Signature MIIIIwYJKoZIhvcNAQcCoIIIFDCCCBACAQExCzAJBgUrDgMCGgUAMAsGCSqGSIb3DQEHAaCC BfQwggLYMIICQaADAgECAgMDIwUwDQYJKoZIhvcNAQEEBQAwgZQxCzAJBgNVBAYTAlpBMRUw EwYDVQQIEwxXZXN0ZXJuIENhcGUxFDASBgNVBAcTC0R1cmJhbnZpbGxlMQ8wDQYDVQQKEwZU aGF3dGUxHTAbBgNVBAsTFENlcnRpZmljYXRlIFNlcnZpY2VzMSgwJgYDVQQDEx9QZXJzb25h bCBGcmVlbWFpbCBSU0EgMTk5OS45LjE2MB4XDTAwMDgyNDIwMzAwOFoXDTAxMDgyNDIwMzAw OFowVDEPMA0GA1UEBBMGRWdnZXJ0MQ0wCwYDVQQqEwRMYXJzMRQwEgYDVQQDEwtMYXJzIEVn Z2VydDEcMBoGCSqGSIb3DQEJARYNbGFyc2VAaXNpLmVkdTCBnzANBgkqhkiG9w0BAQEFAAOB jQAwgYkCgYEAz1yfcNs53rvhuw8gSDvr2+/snP8GduYY7x7WkJdyvcwb4oipNpWYIkMGP214 Zv1KrgvntGaG+jeugAGQt0n64VusgcIzQ6QDRtnMgdQDTAkVSQ2eLRSQka+nAPx6SFKJg79W EEHmgKQBMtZdMBYtYv/mTOcpm7jTJVg+7W6n04UCAwEAAaN3MHUwKgYFK2UBBAEEITAfAgEA MBowGAIBBAQTTDJ1TXlmZkJOVWJOSkpjZFoyczAYBgNVHREEETAPgQ1sYXJzZUBpc2kuZWR1 MAwGA1UdEwEB/wQCMAAwHwYDVR0jBBgwFoAUiKvxYINmVfTkWMdGHcBhvSPXw4wwDQYJKoZI hvcNAQEEBQADgYEAi65fM/jSCaPhRoA9JW5X2FktSFhE5zkIpFVPpv33GWPPNrncsK13HfZm s0B1rNy2vU7UhFI/vsJQgBJyffkLFgMCjp3uRZvBBjGD1q4yjDO5yfMMjquqBpZtRp5op3lT d01faA58ZCB5sxCb0ORSxvXR8tc9DJO0JIpQILa6vIAwggMUMIICfaADAgECAgELMA0GCSqG SIb3DQEBBAUAMIHRMQswCQYDVQQGEwJaQTEVMBMGA1UECBMMV2VzdGVybiBDYXBlMRIwEAYD VQQHEwlDYXBlIFRvd24xGjAYBgNVBAoTEVRoYXd0ZSBDb25zdWx0aW5nMSgwJgYDVQQLEx9D ZXJ0aWZpY2F0aW9uIFNlcnZpY2VzIERpdmlzaW9uMSQwIgYDVQQDExtUaGF3dGUgUGVyc29u YWwgRnJlZW1haWwgQ0ExKzApBgkqhkiG9w0BCQEWHHBlcnNvbmFsLWZyZWVtYWlsQHRoYXd0 ZS5jb20wHhcNOTkwOTE2MTQwMTQwWhcNMDEwOTE1MTQwMTQwWjCBlDELMAkGA1UEBhMCWkEx FTATBgNVBAgTDFdlc3Rlcm4gQ2FwZTEUMBIGA1UEBxMLRHVyYmFudmlsbGUxDzANBgNVBAoT BlRoYXd0ZTEdMBsGA1UECxMUQ2VydGlmaWNhdGUgU2VydmljZXMxKDAmBgNVBAMTH1BlcnNv bmFsIEZyZWVtYWlsIFJTQSAxOTk5LjkuMTYwgZ8wDQYJKoZIhvcNAQEBBQADgY0AMIGJAoGB ALNpWpfU0BYLerXFXekhnCNyzRJMS/d+z8f7ynIk9EJSrFeV43theheE5/1yOTiUtOrtZaeS Bl694GX2GbuUeXZMPrlocHWEHPQRdAC8BSxPCQMXMcz0QdRyxqZd4ohEsIsuxE3x8NaFPmzz lZR4kX5A6ZzRjRVXjsJz5TDeRvVPAgMBAAGjNzA1MBIGA1UdEwEB/wQIMAYBAf8CAQAwHwYD VR0jBBgwFoAUcknCczTGVfQLdnKBfnf0h+fGsg4wDQYJKoZIhvcNAQEEBQADgYEAa8ZZ6TH6 6bbssQPY33Jy/pFgSOrGVd178GeOxmFw523CpTfYnbcXKFYFi91cdW/GkZDGbGZxE9AQfGuR b4bgITYtwdfqsgmtzy1txoNSm/u7/pyHnfy36XSS5FyXrvx+rMoNb3J6Zyxrc/WG+Z31AG70 HQfOnZ6CYynvkwl+Vd4xggH3MIIB8wIBATCBnDCBlDELMAkGA1UEBhMCWkExFTATBgNVBAgT DFdlc3Rlcm4gQ2FwZTEUMBIGA1UEBxMLRHVyYmFudmlsbGUxDzANBgNVBAoTBlRoYXd0ZTEd MBsGA1UECxMUQ2VydGlmaWNhdGUgU2VydmljZXMxKDAmBgNVBAMTH1BlcnNvbmFsIEZyZWVt YWlsIFJTQSAxOTk5LjkuMTYCAwMjBTAJBgUrDgMCGgUAoIGxMBgGCSqGSIb3DQEJAzELBgkq hkiG9w0BBwEwHAYJKoZIhvcNAQkFMQ8XDTAxMDMxNDE3MTU0OVowIwYJKoZIhvcNAQkEMRYE FHLP6eoXC7D8ZrN7h4FFHMTEJLlOMFIGCSqGSIb3DQEJDzFFMEMwCgYIKoZIhvcNAwcwDgYI KoZIhvcNAwICAgCAMAcGBSsOAwIHMA0GCCqGSIb3DQMCAgFAMA0GCCqGSIb3DQMCAgEoMA0G CSqGSIb3DQEBAQUABIGAEGJv8+u4kuhea6i4SLQHsXOXBtFJ4/YA9xftFu/O7m8fOU9HDfmI nVP8Y6BIQ0Vaxuj4nIF9LfisAVtFUTcqbGVRV4KZ+w54RomXfNufgCjJzLsuzxN2xhXVbQcH UDgS7EWOsPUToN+EBt/N+aZ+xbfMsDjiS/WjHAxTohlMVF0= --------------ms0617D6FE6914F636D4A0402D-- To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
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