Re: [freenet-support] Modem lines MTU?
Ben Golding wrote: I think 576 is the recommendation for best performance whether on ADSL or dial-up, several sites seem to confirm this eg: http://www.jimschrempp.com/features/computer/mtuspeed.htm MTU = 1500 is normal for Ethernet LANs. How can I find out the MTU for my dial-up on a W2K machine? Doc ___ Support mailing list Support@freenetproject.org http://news.gmane.org/gmane.network.freenet.support Unsubscribe at http://dodo.freenetproject.org/cgi-bin/mailman/listinfo/support Or mailto:[EMAIL PROTECTED]
Re: [freenet-support] Modem lines MTU?
On Thu, 20 Jan 2005 11:18:47 +0200, Constantine Dokolas [EMAIL PROTECTED] wrote: Ben Golding wrote: I think 576 is the recommendation for best performance whether on ADSL or dial-up, several sites seem to confirm this eg: http://www.jimschrempp.com/features/computer/mtuspeed.htm MTU = 1500 is normal for Ethernet LANs. How can I find out the MTU for my dial-up on a W2K machine? (I'm assuming here you're familiar with the command line) First, get your gateway's IP address with ipconfig. Then, start pinging it with the dont-fragment bit set: ping -f -l 1500 your.gateway.example If you get this error message: Packet needs to be fragmented but DF set., decrease the packet size (1500 bytes), otherwise increase it. Start out with large increases/decreases and keep decreasing the amount you change the packet size. Eventually you'll reach a point where increasing the packet size by one byte results in the error message mentioned above. That is your MTU. ___ Support mailing list Support@freenetproject.org http://news.gmane.org/gmane.network.freenet.support Unsubscribe at http://dodo.freenetproject.org/cgi-bin/mailman/listinfo/support Or mailto:[EMAIL PROTECTED]
Re: [freenet-support] Modem lines MTU?
Mika Hirvonen wrote: On Thu, 20 Jan 2005 11:18:47 +0200, Constantine Dokolas [EMAIL PROTECTED] wrote: Ben Golding wrote: I think 576 is the recommendation for best performance whether on ADSL or dial-up, several sites seem to confirm this eg: http://www.jimschrempp.com/features/computer/mtuspeed.htm MTU = 1500 is normal for Ethernet LANs. How can I find out the MTU for my dial-up on a W2K machine? (I'm assuming here you're familiar with the command line) First, get your gateway's IP address with ipconfig. Then, start pinging it with the dont-fragment bit set: ping -f -l 1500 your.gateway.example If you get this error message: Packet needs to be fragmented but DF set., decrease the packet size (1500 bytes), otherwise increase it. Start out with large increases/decreases and keep decreasing the amount you change the packet size. Eventually you'll reach a point where increasing the packet size by one byte results in the error message mentioned above. That is your MTU. Hmm... I thought there was an easier way... whatever. I must remember old PPP connection logs (or was that some other protocol?). FYI, I tested this in the company LAN and the largest value that got through was 1472. Doc ___ Support mailing list Support@freenetproject.org http://news.gmane.org/gmane.network.freenet.support Unsubscribe at http://dodo.freenetproject.org/cgi-bin/mailman/listinfo/support Or mailto:[EMAIL PROTECTED]
Re: [freenet-support] Modem lines MTU?
On Thu, 20 Jan 2005 11:49:12 +0200, Constantine Dokolas [EMAIL PROTECTED] wrote: Hmm... I thought there was an easier way... whatever. I must remember old PPP connection logs (or was that some other protocol?). Yes, PPP is used to encapsulate TCP/IP over modem lines. PPP's derivates (PPPoE and PPPoA) are used on some ADSL networks. FYI, I tested this in the company LAN and the largest value that got through was 1472. Ethernet's MTU is 1500. IP uses 28 bytes, so that leaves 1472 bytes for data. UDP uses additional 8 bytes and TCP 20 bytes. -- Mika Hirvonen [EMAIL PROTECTED] ___ Support mailing list Support@freenetproject.org http://news.gmane.org/gmane.network.freenet.support Unsubscribe at http://dodo.freenetproject.org/cgi-bin/mailman/listinfo/support Or mailto:[EMAIL PROTECTED]
Re: [freenet-support] Modem lines MTU?
FYI, I tested this in the company LAN and the largest value that got through was 1472. Ethernet's MTU is 1500. IP uses 28 bytes, so that leaves 1472 bytes for data. UDP uses additional 8 bytes and TCP 20 bytes. Thanks Mika, in other words if you can ping with -l 1472 as the maximum, then the max MTU is in fact 28 bytes more (1500). I think it is time to kill this thread unless anyone has any freenet-specific issues with MTUs. Ben ___ Support mailing list Support@freenetproject.org http://news.gmane.org/gmane.network.freenet.support Unsubscribe at http://dodo.freenetproject.org/cgi-bin/mailman/listinfo/support Or mailto:[EMAIL PROTECTED]
Re: [freenet-support] Modem lines MTU?
Yuck! I'm skeptical... Could well be snake oil. Please find me an internet standard that mentions an MTU of 576 bytes - or even some cisco documentation. It seems pretty clear that bigger is better within the limits available... On Wed, Jan 19, 2005 at 04:32:02PM +, Ben Golding wrote: I think 576 is the recommendation for best performance whether on ADSL or dial-up, several sites seem to confirm this eg: http://www.jimschrempp.com/features/computer/mtuspeed.htm MTU = 1500 is normal for Ethernet LANs. Ben Golding -- Matthew J Toseland - [EMAIL PROTECTED] Freenet Project Official Codemonkey - http://freenetproject.org/ ICTHUS - Nothing is impossible. Our Boss says so. signature.asc Description: Digital signature ___ Support mailing list Support@freenetproject.org http://news.gmane.org/gmane.network.freenet.support Unsubscribe at http://dodo.freenetproject.org/cgi-bin/mailman/listinfo/support Or mailto:[EMAIL PROTECTED]
Re: [freenet-support] Modem lines MTU?
On Wed, Jan 19, 2005 at 04:36:11PM +, Toad wrote: Yuck! I'm skeptical... Could well be snake oil. Please find me an internet standard that mentions an MTU of 576 bytes - or even some cisco documentation. It seems pretty clear that bigger is better within the limits available... Bigger=Higher latency. It matters less on most modern ADSL and cable modems as they're high-bandwidth which is throttled, but there are older cable modems where it does give a marked latency decrease. -- Frank v Waveren Fingerprint: BDD7 D61E [EMAIL PROTECTED]|stack.nl] ICQ#10074100 5D39 CF05 4BFC F57A Public key: hkp://wwwkeys.pgp.net/468D62C8 FA00 7D51 468D 62C8 signature.asc Description: Digital signature ___ Support mailing list Support@freenetproject.org http://news.gmane.org/gmane.network.freenet.support Unsubscribe at http://dodo.freenetproject.org/cgi-bin/mailman/listinfo/support Or mailto:[EMAIL PROTECTED]
Re: [freenet-support] Modem lines MTU?
Toad Please find me an internet standard that mentions an MTU of 576 bytes RFC879 HOSTS MUST NOT SEND DATAGRAMS LARGER THAN 576 OCTETS UNLESS THEY RFC879 HAVE SPECIFIC KNOWLEDGE THAT THE DESTINATION HOST IS PREPARED TO RFC879 ACCEPT LARGER DATAGRAMS. RFC879 RFC879 This is a long established rule. http://www.ietf.org/rfc/rfc0879.txt?number=879 I agree, the best MTU is the largest possible without fragmentation, which depends on your ISP and all other routers between yourself and the other host. For example, between my PC at work and www.mit.edu it is 1500. My answer to your original email was saying that a lot of dialup ISPs have a max MTU of 576 and maybe some DSL connections as well. Anyway, here is some interesting info about finding your personal max MTU: http://www.internetweekly.org/llarrow/mtumss.html http://members.tripod.com/~EasyMTU/easymtu/findmtu.html and some related tweaking info about Receive Window size for the curious among you. http://www.dslreports.com/tweaks/RWIN Ben ___ Support mailing list Support@freenetproject.org http://news.gmane.org/gmane.network.freenet.support Unsubscribe at http://dodo.freenetproject.org/cgi-bin/mailman/listinfo/support Or mailto:[EMAIL PROTECTED]
Re: [freenet-support] Modem lines MTU?
Are you saying that hosts are required to support MTUs of at least 576 bytes? People have said that some dialup connections use 256 byte MTUs... On Wed, Jan 19, 2005 at 06:04:25PM +, Ben Golding wrote: Toad Please find me an internet standard that mentions an MTU of 576 bytes RFC879 HOSTS MUST NOT SEND DATAGRAMS LARGER THAN 576 OCTETS UNLESS THEY RFC879 HAVE SPECIFIC KNOWLEDGE THAT THE DESTINATION HOST IS PREPARED TO RFC879 ACCEPT LARGER DATAGRAMS. RFC879 RFC879 This is a long established rule. http://www.ietf.org/rfc/rfc0879.txt?number=879 I agree, the best MTU is the largest possible without fragmentation, which depends on your ISP and all other routers between yourself and the other host. For example, between my PC at work and www.mit.edu it is 1500. My answer to your original email was saying that a lot of dialup ISPs have a max MTU of 576 and maybe some DSL connections as well. Anyway, here is some interesting info about finding your personal max MTU: http://www.internetweekly.org/llarrow/mtumss.html http://members.tripod.com/~EasyMTU/easymtu/findmtu.html and some related tweaking info about Receive Window size for the curious among you. http://www.dslreports.com/tweaks/RWIN Ben -- Matthew J Toseland - [EMAIL PROTECTED] Freenet Project Official Codemonkey - http://freenetproject.org/ ICTHUS - Nothing is impossible. Our Boss says so. signature.asc Description: Digital signature ___ Support mailing list Support@freenetproject.org http://news.gmane.org/gmane.network.freenet.support Unsubscribe at http://dodo.freenetproject.org/cgi-bin/mailman/listinfo/support Or mailto:[EMAIL PROTECTED]
Re: [freenet-support] Modem lines MTU?
On Wed, 19 Jan 2005 19:16:44 +, Toad [EMAIL PROTECTED] wrote: Are you saying that hosts are required to support MTUs of at least 576 bytes? People have said that some dialup connections use 256 byte MTUs... Hrm. Dialup. The MTU includes the PPP header is max. 30 bytes, IP header can be a maximum of 60 bytes and UDP is a further 8 bytes.. That's 98 bytes of header, leaving 158 bytes of data. So the header is 38% of the packet? That sounds absurd... Of course, PPP can use header compression on the PPP and IP headers, leaving the PPP header at ~4 bytes and IP at ~20, leading to a 38 byte header (14%), but it's still a small packet, considering that an uncompressed header set over an ethernet (1500) MTU is 6%. On Windows the lowest possible MTU is apparently (http://techrepublic.com.com/5100-6268-1061241.html) 68 bytes, but that's absurd. Since you're supposed to send 576 byte packets anyway if PMTU discovery doesn't work then I'd go for that figure. If things start dropping, or more likely the client's ISP starts sending must-fragment ICMP packets, then throttle back. Of course, if the computer you're trying to connect from has a stupidly low MTU, AND a stupid firewall that blocks incoming ICMP then the user really deserves what they're getting. I've been known to be particularly unpleasent to individuals who think blocking an essential control protcol is a good idea. -- Phillip Hutchings http://www.sitharus.com/ [EMAIL PROTECTED] / [EMAIL PROTECTED] ___ Support mailing list Support@freenetproject.org http://news.gmane.org/gmane.network.freenet.support Unsubscribe at http://dodo.freenetproject.org/cgi-bin/mailman/listinfo/support Or mailto:[EMAIL PROTECTED]
Re: [freenet-support] Modem lines MTU?
On Wed, 19 Jan 2005, Toad wrote: Are you saying that hosts are required to support MTUs of at least 576 bytes? People have said that some dialup connections use 256 byte MTUs... RFC879 HOSTS MUST NOT SEND DATAGRAMS LARGER THAN 576 OCTETS UNLESS Isn't MTU something which is negotiated nowadays? I suspect the 256-MTU ISPs would support higher MTUs like everyone else if you forced PPP to do it. Magnus ___ Support mailing list Support@freenetproject.org http://news.gmane.org/gmane.network.freenet.support Unsubscribe at http://dodo.freenetproject.org/cgi-bin/mailman/listinfo/support Or mailto:[EMAIL PROTECTED]
Re: [freenet-support] Modem lines MTU?
On Wed, 19 Jan 2005 18:04:25 +, Ben Golding [EMAIL PROTECTED] wrote: Anyway, here is some interesting info about finding your personal max MTU: http://www.internetweekly.org/llarrow/mtumss.html http://members.tripod.com/~EasyMTU/easymtu/findmtu.html Nifty. I'm getting somewhere between 1460 and 1470 on my SBC ADSL. -todd ___ Support mailing list Support@freenetproject.org http://news.gmane.org/gmane.network.freenet.support Unsubscribe at http://dodo.freenetproject.org/cgi-bin/mailman/listinfo/support Or mailto:[EMAIL PROTECTED]
