Re: setting the other end's TCP segment size
1) create a static ARP entry, this will create an entry to the routing table i.e. arp -S IPADDR MACADDR 2) modify the mtu for that destination i.e. route change IPADDR -mtu MTU Seems to work fine :) One problem with this approach is that a hard-coded MAC address would break if the destination's MAC address changed :( but this can be scripted around by pinging the destination (to ensure that it's up, and get an arp entry the usual way), then reading the MAC address from the arp table. d=192.168.200.3 ping -c 1 $d \ arp -S $d ` arp -n $d | sed -e 's/^.* at //' -e 's/ on .*$//' ` \ route change $d -mtu 640 ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: setting the other end's TCP segment size
On Monday 04 August 2008 00:16:54 [EMAIL PROTECTED] wrote: Is there a simple way for a FreeBSD system to cause its peer to use a transmit segment size of, say, 640 bytes -- so that the peer will never try to send a packet larger than that? I'm trying to get around a network packet-size problem. In case it matters, the other end is SunOS 4.1.1 on a sun3, and I've been unable to find a way to limit its packet size directly. ... Each tcp conversation can have it's own size set along with a bunch of other params. Good point. The TCP_MAXSEG can reduce the maximum segment size for a single TCP connection to something smaller than the interface MTU :) That would be OK, provided I could somehow arrange for it to apply to all conversations with this particular destination (which is what the next item seems to do :) Just adding that MTU can be set per destination with the help of route(8) and the -mtu modifier. That would be better than setting the local mtu -- which has been causing other problems although it takes care of the original -- and it is a better match to the physical situation. (The culprit is neither the Sun nor the FreeBSD system, but the physical link between the Sun and the hub.) What I haven't been able to come up with is a way of making such a setting permanent. If I've communicated with the Sun recently enough, netstat -r -W reports a line like this (some spaces removed, for length, and I've no longer got xl0's mtu set low) Destination Gateway Flags Refs Use Mtu Netif Expire 192.168.200.3 08:00:20:00:a7:a6 UHLW 1 34 1500 xl0 1184 Now if I do # route change 192.168.200.3 -lock -mtu 640 the mtu column changes to 640 and it works fine, but only until the routing entry expires. Adding -static makes no difference -- the entry still expires and loses the mtu specification. I've been unable to come up with a route command that will *create* an entry like that (vs modifying an existing one), nor that will transform a transient entry into a permanent one. Yes, it's the interaction of ARP and the routing subsystem. I am sure there is a shorter way for doing this, but it escapes my knowledge: 1) create a static ARP entry, this will create an entry to the routing table i.e. arp -S IPADDR MACADDR 2) modify the mtu for that destination i.e. route change IPADDR -mtu MTU HTH, Nikos ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: setting the other end's TCP segment size
Is there a simple way for a FreeBSD system to cause its peer to use a transmit segment size of, say, 640 bytes -- so that the peer will never try to send a packet larger than that? I'm trying to get around a network packet-size problem. In case it matters, the other end is SunOS 4.1.1 on a sun3, and I've been unable to find a way to limit its packet size directly. ... Each tcp conversation can have it's own size set along with a bunch of other params. Good point. The TCP_MAXSEG can reduce the maximum segment size for a single TCP connection to something smaller than the interface MTU :) That would be OK, provided I could somehow arrange for it to apply to all conversations with this particular destination (which is what the next item seems to do :) Just adding that MTU can be set per destination with the help of route(8) and the -mtu modifier. That would be better than setting the local mtu -- which has been causing other problems although it takes care of the original -- and it is a better match to the physical situation. (The culprit is neither the Sun nor the FreeBSD system, but the physical link between the Sun and the hub.) What I haven't been able to come up with is a way of making such a setting permanent. If I've communicated with the Sun recently enough, netstat -r -W reports a line like this (some spaces removed, for length, and I've no longer got xl0's mtu set low) Destination Gateway Flags Refs Use Mtu Netif Expire 192.168.200.3 08:00:20:00:a7:a6 UHLW 1 34 1500 xl0 1184 Now if I do # route change 192.168.200.3 -lock -mtu 640 the mtu column changes to 640 and it works fine, but only until the routing entry expires. Adding -static makes no difference -- the entry still expires and loses the mtu specification. I've been unable to come up with a route command that will *create* an entry like that (vs modifying an existing one), nor that will transform a transient entry into a permanent one. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: setting the other end's TCP segment size
On Thursday 31 July 2008 01:21:25 Giorgos Keramidas wrote: On Wed, 30 Jul 2008 16:20:06 -0500, Derek Ragona [EMAIL PROTECTED] wrote: At 11:04 PM 7/29/2008, [EMAIL PROTECTED] wrote: [TCP] splits traffic to 'segments' using its own logic ... Is there a simple way for a FreeBSD system to cause its peer to use a transmit segment size of, say, 640 bytes -- so that the peer will never try to send a packet larger than that? I'm trying to get around a network packet-size problem. In case it matters, the other end is SunOS 4.1.1 on a sun3, and I've been unable to find a way to limit its packet size directly. Just as an FYI, you might want to do: man setsockopt ro man getsockopt Each tcp conversation can have it's own size set along with a bunch of other params. Good point. The TCP_MAXSEG can reduce the maximum segment size for a single TCP connection to something smaller than the interface MTU :) Just adding that MTU can be set per destination with the help of route(8) and the -mtu modifier. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: setting the other end's TCP segment size
You can edit `/etc/hostname.foo0' in the Sun too, and add something like: 192.168.1.10/24 mtu 640 [getting OT for FreeBSD] Are you sure that works as far back as SunOS 4.1.1? /etc/hostname.le0 currently consists of the single word pluto and it looks as if this causes /etc/rc.boot to do ifconfig le0 pluto netmask + -trailers up (where the name pluto resolves to 192.168.200.1 via /etc/hosts). If I were to change /etc/hostname.le0 to pluto mtu 640 I think the ifconfig command would become ifconfig le0 pluto mtu 640 netmask + -trailers up and it doesn't look as if ifconfig recognizes mtu as a keyword (at least while running -- granted I haven't tried actually editing /etc/hostname.le0 and rebooting): # ifconfig le0 pluto mtu 640 ifconfig: mtu: bad address ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: setting the other end's TCP segment size
On Thu, 31 Jul 2008 01:43:11 -0700, [EMAIL PROTECTED] wrote: You can edit `/etc/hostname.foo0' in the Sun too, and add something like: 192.168.1.10/24 mtu 640 [getting OT for FreeBSD] Are you sure that works as far back as SunOS 4.1.1? Ah! That will not work, you are right. When I saw 'Sun' I assumed a relatively recent Solaris version. I didn't know you had SunOS 4.1.1 still around! :) ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: setting the other end's TCP segment size
Is there a simple way for a FreeBSD system to cause its peer to use a transmit segment size of, say, 640 bytes -- so that the peer will never try to send a packet larger than that? I'm trying to get around a network packet-size problem. In case it matters, the other end is SunOS 4.1.1 on a sun3, and I've been unable to find a way to limit its packet size directly. Setting the interface MTU should do it, i.e.: ifconfig re0 mtu 640 Not all interfaces support setting the MTU and some may have range restrictions though. In particular, this seems to work with my wlan0 interface, but not with my re0 interface ... That's certainly simple enough, and xl0 apparently supports the reduced mtu setting. It seems to be working just fine. Thanks! I'd thought of trying to set the sun's MTU, but hadn't been able to find a way to do it. It had never occurred to me that setting the *recipient's* MTU would limit the *sender's* packet size. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: setting the other end's TCP segment size
On Wed, 30 Jul 2008 00:09:45 -0700, [EMAIL PROTECTED] wrote: Is there a simple way for a FreeBSD system to cause its peer to use a transmit segment size of, say, 640 bytes -- so that the peer will never try to send a packet larger than that? I'm trying to get around a network packet-size problem. In case it matters, the other end is SunOS 4.1.1 on a sun3, and I've been unable to find a way to limit its packet size directly. Setting the interface MTU should do it, i.e.: ifconfig re0 mtu 640 Not all interfaces support setting the MTU and some may have range restrictions though. In particular, this seems to work with my wlan0 interface, but not with my re0 interface ... That's certainly simple enough, and xl0 apparently supports the reduced mtu setting. It seems to be working just fine. Thanks! I'd thought of trying to set the sun's MTU, but hadn't been able to find a way to do it. It had never occurred to me that setting the *recipient's* MTU would limit the *sender's* packet size. You can edit `/etc/hostname.foo0' in the Sun too, and add something like: 192.168.1.10/24 mtu 640 but since now you are happy with the new setup, that's fine :) ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: setting the other end's TCP segment size
At 11:04 PM 7/29/2008, [EMAIL PROTECTED] wrote: [TCP] splits traffic to 'segments' using its own logic ... Is there a simple way for a FreeBSD system to cause its peer to use a transmit segment size of, say, 640 bytes -- so that the peer will never try to send a packet larger than that? I'm trying to get around a network packet-size problem. In case it matters, the other end is SunOS 4.1.1 on a sun3, and I've been unable to find a way to limit its packet size directly. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED] -- Just as an FYI, you might want to do: man setsockopt ro man getsockopt Each tcp conversation can have it's own size set along with a bunch of other params. -Derek -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: setting the other end's TCP segment size
On Wed, 30 Jul 2008 16:20:06 -0500, Derek Ragona [EMAIL PROTECTED] wrote: At 11:04 PM 7/29/2008, [EMAIL PROTECTED] wrote: [TCP] splits traffic to 'segments' using its own logic ... Is there a simple way for a FreeBSD system to cause its peer to use a transmit segment size of, say, 640 bytes -- so that the peer will never try to send a packet larger than that? I'm trying to get around a network packet-size problem. In case it matters, the other end is SunOS 4.1.1 on a sun3, and I've been unable to find a way to limit its packet size directly. Just as an FYI, you might want to do: man setsockopt ro man getsockopt Each tcp conversation can have it's own size set along with a bunch of other params. Good point. The TCP_MAXSEG can reduce the maximum segment size for a single TCP connection to something smaller than the interface MTU :) ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
setting the other end's TCP segment size
[TCP] splits traffic to 'segments' using its own logic ... Is there a simple way for a FreeBSD system to cause its peer to use a transmit segment size of, say, 640 bytes -- so that the peer will never try to send a packet larger than that? I'm trying to get around a network packet-size problem. In case it matters, the other end is SunOS 4.1.1 on a sun3, and I've been unable to find a way to limit its packet size directly. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: setting the other end's TCP segment size
On Wed, 30 Jul 2008 07:36:34 +0300, Giorgos Keramidas [EMAIL PROTECTED] wrote: On Tue, 29 Jul 2008 21:04:53 -0700, [EMAIL PROTECTED] wrote: [TCP] splits traffic to 'segments' using its own logic ... Is there a simple way for a FreeBSD system to cause its peer to use a transmit segment size of, say, 640 bytes -- so that the peer will never try to send a packet larger than that? I'm trying to get around a network packet-size problem. In case it matters, the other end is SunOS 4.1.1 on a sun3, and I've been unable to find a way to limit its packet size directly. Setting the interface MTU should do it, i.e.: ifconfig re0 mtu 640 Not all interfaces support setting the MTU and some may have range restrictions though. In particular, this seems to work with my wlan0 interface, but not with my re0 interface. The wlan0 interface correctly limits the maximum TCP segment size to 500 bytes when I set the MTU: # ifconfig wlan0 | fgrep mtu wlan0: flags=8843UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST metric 0 mtu 1500 # ifconfig wlan0 down; ifconfig wlan0 mtu 50 up Then a tcpdump to save SSH traffic to a particular host, and a dump of the resulting pcap shows: # tcpdump -s 2000 -l -vvv -w save.pcap 'host a.b.c.d port 22' Got 42^C # echo ` tcpdump -n -l -vvv -r save.pcap 2/dev/null | \ sed -e 's/.* length //' -e 's/).*//' ` | fmt 60 60 52 91 52 91 500 500 340 356 52 52 76 204 196 500 260 52 68 52 100 100 116 116 500 132 52 500 84 52 500 196 52 84 116 100 164 436 52 100 132 52 This should work for *both* sides of the connection because of the initial maximum segment size negotiation between the two TCP hosts. See for example the two first packets of the capture I mentioned above, and look for the 'mss' option: 07:38:19.554338 IP (tos 0x0, ttl 64, id 44805, offset 0, flags [DF], proto TCP (6), length 60) 192.168.1.???.53468 X.Y.Z.W.22: S, cksum 0x20d6 (correct), 4195632487:4195632487(0) win 65535 mss 460,nop,wscale 3,sackOK,timestamp 62534308 0 07:38:19.591065 IP (tos 0x0, ttl 54, id 39804, offset 0, flags [DF], proto TCP (6), length 60) X.Y.Z.W.22 192.168.1.???.53468: S, cksum 0x7f2f (correct), 901580944:901580944(0) ack 4195632488 win 65535 mss 460,nop,wscale 3,sackOK,timestamp 3188303166 62534308 The MSS advertised is less than 500 to leave some space for the IP and TCP headers, but the full IP datagram _length_ that I displayed in the fmt(1) output above shows that the full MTU is used some times for the IP datagrams sent or received. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: setting the other end's TCP segment size
On Tue, 29 Jul 2008 21:04:53 -0700, [EMAIL PROTECTED] wrote: [TCP] splits traffic to 'segments' using its own logic ... Is there a simple way for a FreeBSD system to cause its peer to use a transmit segment size of, say, 640 bytes -- so that the peer will never try to send a packet larger than that? I'm trying to get around a network packet-size problem. In case it matters, the other end is SunOS 4.1.1 on a sun3, and I've been unable to find a way to limit its packet size directly. Setting the interface MTU should do it, i.e.: ifconfig re0 mtu 640 Not all interfaces support setting the MTU and some may have range restrictions though. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
