I have been having trouble with anoncvs (over ssh) to
anoncvs.netbsd.org.  Looking at traces, it seemed that cvs operations
that did not cause my machine to send MTU-sized segments succeeded,
and those that did failed.  I experimented to find the critical value.
MTU 1476 works, and 1477 loses.  example losing/winning tcpdumps
follow.  I have also seen behavior where the large segment is
continually retransmitted, with no resets received.


letrec.ir.bbn.com is a normal dell pc running 1.5.3-RC (anoncvs from
20020510).  Given the round-trip times implied by the resets below,
they seem to be coming from something close to anoncvs.netbsd.org.  I
can't swear that nothing is broken in my local environment, but I
don't have any reason to suspect any (relevant) breakage.

With '-mtu 1480' on a route:
08:47:02.186513 letrec.ir.BBN.com.65512 > nbanoncvs2.isc.org.ssh: S 3963873951:3963873951(0) win 16384 <mss 1460,nop,wscale 0,nop,nop,timestamp 180681 0>
08:47:02.267166 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65512: S 792266061:792266061(0) ack 3963873952 win 32768 <mss 1460,nop,wscale 0,nop,nop,timestamp 604097 180681>
08:47:02.267193 letrec.ir.BBN.com.65512 > nbanoncvs2.isc.org.ssh: . ack 1 win 17520 <nop,nop,timestamp 180681 604097>
08:47:02.355788 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65512: P 1:53(52) ack 1 win 33580 <nop,nop,timestamp 604097 0>
08:47:02.356026 letrec.ir.BBN.com.65512 > nbanoncvs2.isc.org.ssh: P 1:52(51) ack 53 win 17520 <nop,nop,timestamp 180681 604097>
08:47:02.453939 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65512: P 53:693(640) ack 52 win 33580 <nop,nop,timestamp 604097 180681>
08:47:02.453984 letrec.ir.BBN.com.65512 > nbanoncvs2.isc.org.ssh: P 52:684(632) ack 693 win 16880 <nop,nop,timestamp 180681 604097>
08:47:02.539291 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65512: . ack 684 win 33580 <nop,nop,timestamp 604097 180681>
08:47:02.539313 letrec.ir.BBN.com.65512 > nbanoncvs2.isc.org.ssh: P 684:708(24) ack 693 win 17520 <nop,nop,timestamp 180682 604097>
08:47:02.670882 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65512: P 693:1117(424) ack 708 win 33580 <nop,nop,timestamp 604098 180682>
08:47:02.820028 letrec.ir.BBN.com.65512 > nbanoncvs2.isc.org.ssh: . ack 1117 win 17520 <nop,nop,timestamp 180682 604098>
08:47:02.957935 letrec.ir.BBN.com.65512 > nbanoncvs2.isc.org.ssh: P 708:1124(416) ack 1117 win 17520 <nop,nop,timestamp 180682 604098>
08:47:03.136499 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65512: . ack 1124 win 33164 <nop,nop,timestamp 604098 180682>
08:47:03.881611 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65512: P 1117:1853(736) ack 1124 win 33580 <nop,nop,timestamp 604100 180682>
08:47:04.020040 letrec.ir.BBN.com.65512 > nbanoncvs2.isc.org.ssh: . ack 1853 win 17520 <nop,nop,timestamp 180685 604100>
08:47:04.164032 letrec.ir.BBN.com.65512 > nbanoncvs2.isc.org.ssh: P 1124:1140(16) ack 1853 win 17520 <nop,nop,timestamp 180685 604100>
08:47:04.332935 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65512: . ack 1140 win 33580 <nop,nop,timestamp 604101 180685>
08:47:04.332972 letrec.ir.BBN.com.65512 > nbanoncvs2.isc.org.ssh: P 1140:1188(48) ack 1853 win 17520 <nop,nop,timestamp 180685 604100>
08:47:04.412865 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65512: P 1853:1901(48) ack 1188 win 33580 <nop,nop,timestamp 604101 180685>
08:47:04.413346 letrec.ir.BBN.com.65512 > nbanoncvs2.isc.org.ssh: P 1188:1252(64) ack 1901 win 17520 <nop,nop,timestamp 180685 604101>
08:47:04.504764 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65512: P 1901:1933(32) ack 1252 win 33580 <nop,nop,timestamp 604101 180685>
08:47:04.504996 letrec.ir.BBN.com.65512 > nbanoncvs2.isc.org.ssh: P 1252:1316(64) ack 1933 win 17520 <nop,nop,timestamp 180685 604101>
08:47:04.585122 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65512: P 1933:1981(48) ack 1316 win 33580 <nop,nop,timestamp 604101 180685>
08:47:04.585292 letrec.ir.BBN.com.65512 > nbanoncvs2.isc.org.ssh: P 1316:1380(64) ack 1981 win 17520 <nop,nop,timestamp 180686 604101> [tos 0x8]
08:47:04.669281 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65512: P 1981:2029(48) ack 1380 win 33580 <nop,nop,timestamp 604102 180686> [tos 0x8]
08:47:04.669428 letrec.ir.BBN.com.65512 > nbanoncvs2.isc.org.ssh: P 1380:1796(416) ack 2029 win 17520 <nop,nop,timestamp 180686 604102> [tos 0x8]
08:47:04.751942 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65512: P 2029:2573(544) ack 1796 win 33580 <nop,nop,timestamp 604102 180686> [tos 0x8]
08:47:04.755698 letrec.ir.BBN.com.65512 > nbanoncvs2.isc.org.ssh: . 1796:3224(1428) ack 2573 win 17520 <nop,nop,timestamp 180686 604102> [tos 0x8]
08:47:04.838952 nbanoncvs2.isc.org.23858 > letrec.ir.BBN.com.36421: R 0:0(0) ack 0 win 0 [tos 0x8]
08:47:05.665996 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65512: P 2029:2573(544) ack 1796 win 33580 <nop,nop,timestamp 604103 180686> [tos 0x8]
08:47:05.666024 letrec.ir.BBN.com.65512 > nbanoncvs2.isc.org.ssh: P 3224:4212(988) ack 2573 win 17520 <nop,nop,timestamp 180688 604102> [tos 0x8]
08:47:05.748242 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65512: . ack 1796 win 33580 <nop,nop,timestamp 604104 180686> [tos 0x8]
08:47:06.020020 letrec.ir.BBN.com.65512 > nbanoncvs2.isc.org.ssh: . 1796:3224(1428) ack 2573 win 17520 <nop,nop,timestamp 180688 604102> [tos 0x8]
08:47:06.102203 nbanoncvs2.isc.org.23858 > letrec.ir.BBN.com.36421: R 0:0(0) ack 1 win 0 [tos 0x8]
08:47:09.020025 letrec.ir.BBN.com.65512 > nbanoncvs2.isc.org.ssh: . 1796:3224(1428) ack 2573 win 17520 <nop,nop,timestamp 180694 604102> [tos 0x8]
08:47:09.103018 nbanoncvs2.isc.org.23858 > letrec.ir.BBN.com.36421: R 0:0(0) ack 1 win 0 [tos 0x8]
08:47:15.020027 letrec.ir.BBN.com.65512 > nbanoncvs2.isc.org.ssh: . 1796:3224(1428) ack 2573 win 17520 <nop,nop,timestamp 180706 604102> [tos 0x8]
08:47:15.102435 nbanoncvs2.isc.org.23858 > letrec.ir.BBN.com.36421: R 0:0(0) ack 1 win 0 [tos 0x8]

With '-mtu 1460':

08:48:13.357794 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65511: S 3272139089:3272139089(0) ack 2075305622 win 32768 <mss 1460,nop,wscale 0,nop,nop,timestamp 604239 180823>
08:48:13.357832 letrec.ir.BBN.com.65511 > nbanoncvs2.isc.org.ssh: . ack 1 win 17520 <nop,nop,timestamp 180823 604239>
08:48:13.442599 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65511: P 1:53(52) ack 1 win 33580 <nop,nop,timestamp 604239 0>
08:48:13.442850 letrec.ir.BBN.com.65511 > nbanoncvs2.isc.org.ssh: P 1:52(51) ack 53 win 17520 <nop,nop,timestamp 180823 604239>
08:48:13.526378 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65511: P 53:693(640) ack 52 win 33580 <nop,nop,timestamp 604239 180823>
08:48:13.526414 letrec.ir.BBN.com.65511 > nbanoncvs2.isc.org.ssh: P 52:684(632) ack 693 win 16880 <nop,nop,timestamp 180824 604239>
08:48:13.656539 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65511: . ack 684 win 33580 <nop,nop,timestamp 604239 180824>
08:48:13.656559 letrec.ir.BBN.com.65511 > nbanoncvs2.isc.org.ssh: P 684:708(24) ack 693 win 17520 <nop,nop,timestamp 180824 604239>
08:48:13.770248 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65511: P 693:1117(424) ack 708 win 33580 <nop,nop,timestamp 604240 180824>
08:48:13.820025 letrec.ir.BBN.com.65511 > nbanoncvs2.isc.org.ssh: . ack 1117 win 17520 <nop,nop,timestamp 180824 604240>
08:48:14.051560 letrec.ir.BBN.com.65511 > nbanoncvs2.isc.org.ssh: P 708:1124(416) ack 1117 win 17520 <nop,nop,timestamp 180825 604240>
08:48:14.253954 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65511: . ack 1124 win 33164 <nop,nop,timestamp 604241 180825>
08:48:15.865571 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65511: P 1117:1853(736) ack 1124 win 33580 <nop,nop,timestamp 604244 180825>
08:48:16.020046 letrec.ir.BBN.com.65511 > nbanoncvs2.isc.org.ssh: . ack 1853 win 17520 <nop,nop,timestamp 180829 604244>
08:48:16.148733 letrec.ir.BBN.com.65511 > nbanoncvs2.isc.org.ssh: P 1124:1140(16) ack 1853 win 17520 <nop,nop,timestamp 180829 604244>
08:48:16.246035 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65511: . ack 1140 win 33580 <nop,nop,timestamp 604245 180829>
08:48:16.246077 letrec.ir.BBN.com.65511 > nbanoncvs2.isc.org.ssh: P 1140:1188(48) ack 1853 win 17520 <nop,nop,timestamp 180829 604244>
? anoncvs
cvs server: Updating .
08:48:16.352759 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65511: P 1853:1901(48) ack 1188 win 33580 <nop,nop,timestamp 604245 180829>
08:48:16.353362 letrec.ir.BBN.com.65511 > nbanoncvs2.isc.org.ssh: P 1188:1252(64) ack 1901 win 17520 <nop,nop,timestamp 180829 604245>
08:48:16.446479 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65511: . ack 1252 win 33580 <nop,nop,timestamp 604245 180829>
08:48:16.506821 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65511: P 1901:1933(32) ack 1252 win 33580 <nop,nop,timestamp 604245 180829>
08:48:16.507066 letrec.ir.BBN.com.65511 > nbanoncvs2.isc.org.ssh: P 1252:1316(64) ack 1933 win 17520 <nop,nop,timestamp 180829 604245>
08:48:16.587482 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65511: P 1933:1981(48) ack 1316 win 33580 <nop,nop,timestamp 604245 180829>
08:48:16.587640 letrec.ir.BBN.com.65511 > nbanoncvs2.isc.org.ssh: P 1316:1380(64) ack 1981 win 17520 <nop,nop,timestamp 180830 604245> [tos 0x8]
08:48:16.671216 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65511: P 1981:2029(48) ack 1380 win 33580 <nop,nop,timestamp 604246 180830> [tos 0x8]
08:48:16.671358 letrec.ir.BBN.com.65511 > nbanoncvs2.isc.org.ssh: P 1380:1796(416) ack 2029 win 17520 <nop,nop,timestamp 180830 604246> [tos 0x8]
08:48:16.773448 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65511: P 2029:2573(544) ack 1796 win 33580 <nop,nop,timestamp 604246 180830> [tos 0x8]
08:48:16.777201 letrec.ir.BBN.com.65511 > nbanoncvs2.isc.org.ssh: . 1796:3204(1408) ack 2573 win 17520 <nop,nop,timestamp 180830 604246> [tos 0x8]
08:48:17.042949 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65511: . ack 3204 win 33580 <nop,nop,timestamp 604246 180830> [tos 0x8]
08:48:17.042975 letrec.ir.BBN.com.65511 > nbanoncvs2.isc.org.ssh: P 3204:4212(1008) ack 2573 win 17520 <nop,nop,timestamp 180831 604246> [tos 0x8]
08:48:17.134357 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65511: P 2573:2621(48) ack 4212 win 33580 <nop,nop,timestamp 604246 180831> [tos 0x8]
08:48:17.220025 letrec.ir.BBN.com.65511 > nbanoncvs2.isc.org.ssh: . ack 2621 win 17520 <nop,nop,timestamp 180831 604246> [tos 0x8]
08:48:17.299511 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65511: P 2621:2685(64) ack 4212 win 33580 <nop,nop,timestamp 604247 180831> [tos 0x8]
cvs server: Updating bulk
08:48:17.420020 letrec.ir.BBN.com.65511 > nbanoncvs2.isc.org.ssh: . ack 2685 win 17520 <nop,nop,timestamp 180831 604247> [tos 0x8]
08:48:17.916926 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65511: P 2685:2749(64) ack 4212 win 33580 <nop,nop,timestamp 604248 180831> [tos 0x8]
08:48:18.020025 letrec.ir.BBN.com.65511 > nbanoncvs2.isc.org.ssh: . ack 2749 win 17520 <nop,nop,timestamp 180833 604248> [tos 0x8]
cvs server: Updating install
letrec gdt 58 /usr/pkgsrc/mk > 08:48:18.519990 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65511: P 2749:2829(80) ack 4212 win 33580 <nop,nop,timestamp 604249 180831> [tos 0x8]
08:48:18.620015 letrec.ir.BBN.com.65511 > nbanoncvs2.isc.org.ssh: . ack 2829 win 17520 <nop,nop,timestamp 180834 604249> [tos 0x8]
08:48:18.735314 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65511: P 2829:2877(48) ack 4212 win 33580 <nop,nop,timestamp 604250 180831> [tos 0x8]
08:48:18.735985 letrec.ir.BBN.com.65511 > nbanoncvs2.isc.org.ssh: P 4212:4244(32) ack 2877 win 17520 <nop,nop,timestamp 180834 604250> [tos 0x8]
08:48:18.820911 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65511: P 2877:3005(128) ack 4244 win 33580 <nop,nop,timestamp 604250 180834> [tos 0x8]
08:48:18.821114 letrec.ir.BBN.com.65511 > nbanoncvs2.isc.org.ssh: P 4244:4276(32) ack 3005 win 17520 <nop,nop,timestamp 180834 604250> [tos 0x8]
08:48:18.821221 letrec.ir.BBN.com.65511 > nbanoncvs2.isc.org.ssh: F 4276:4276(0) ack 3005 win 17520 <nop,nop,timestamp 180834 604250> [tos 0x8]
08:48:18.902012 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65511: . ack 4277 win 33580 <nop,nop,timestamp 604250 180834> [tos 0x8]
08:48:18.902022 nbanoncvs2.isc.org.ssh > letrec.ir.BBN.com.65511: F 3005:3005(0) ack 4277 win 33580 <nop,nop,timestamp 604250 180834> [tos 0x8]
08:48:18.902077 letrec.ir.BBN.com.65511 > nbanoncvs2.isc.org.ssh: . ack 3006 win 17519 <nop,nop,timestamp 180834 604250> [tos 0x8]

traceroute to anoncvs.netbsd.org

traceroute to anoncvs.netbsd.org (204.152.184.161), 30 hops max, 40 byte packets
 1  CAM-EXTERNAL.BBN.com (192.1.100.1)  0.923 ms  0.480 ms  0.432 ms
 2  192.1.101.82 (192.1.101.82)  0.523 ms  0.437 ms  0.483 ms
 3  s9-1-1.cambridge1-cr18.bbnplanet.net (4.1.138.37)  0.902 ms  0.642 ms  0.573 ms
 4  p1-1.cambridge1-nbr1.bbnplanet.net (4.0.5.73)  1.421 ms  0.642 ms  0.592 ms
 5  p3-0.cambridge1-nbr2.bbnplanet.net (4.0.5.18)  0.777 ms  0.603 ms  0.698 ms
 6  so-4-2-0.bstnma1-nbr2.bbnplanet.net (4.0.2.249)  1.941 ms  1.382 ms  1.126 ms
 7  p9-0.nycmny1-nbr2.bbnplanet.net (4.24.6.50)  7.662 ms  7.474 ms  7.299 ms
 8  p15-0.nycmny1-nbr1.bbnplanet.net (4.24.10.209)  7.607 ms  7.628 ms  7.512 ms
 9  p1-0.nycmny1-cr11.bbnplanet.net (4.24.10.77)  7.475 ms  7.325 ms  7.311 ms
10  if-1-6.core1.NewYork.Teleglobe.net (207.45.196.145)  26.496 ms  24.921 ms  24.517 ms
11  if-2-0.core1.PaloAlto.Teleglobe.net (64.86.83.201)  74.743 ms  74.783 ms  75.054 ms
12  207.45.196.66 (207.45.196.66)  79.294 ms  78.660 ms  78.879 ms
13  so-1-0-0.orpa8.pf.isc.org (192.5.4.231)  78.868 ms  78.862 ms  78.803 ms
14  tun0.orrc5.pf.isc.org (192.5.4.165)  79.169 ms  78.721 ms  79.269 ms
15  nbanoncvs.isc.org (204.152.186.167)  79.323 ms  79.611 ms  79.737 ms