Снял дамп соединения с роутера, смотрящего в инет (к нему подключен пппое-сервер, к которому подключена кошка):
x.x.x.x - кошка
y.y.y.y - пппое-сервер
12:53:32.225367 00:15:17:ab:6a:7e > 00:1f:12:14:e6:36, ethertype IPv4 (0x0800), length 66: x.x.x.x.60863 > 195.82.146.114.80: S 2784157706:2784157706(0) win 5840 <mss 1452,nop,nop,sackOK,nop,wscale 6>
12:53:32.354814 00:1f:12:14:e6:36 > 00:15:17:ab:6a:7e, ethertype IPv4 (0x0800), length 60: 195.82.146.114.80 > x.x.x.x.60863: S 264825784:264825784(0) ack 2784157707 win 5840 <mss 1460>
12:53:32.356508 00:15:17:ab:6a:7e > 00:1f:12:14:e6:36, ethertype IPv4 (0x0800), length 54: x.x.x.x.60863 > 195.82.146.114.80: . ack 1 win 5840
12:53:32.357101 00:15:17:ab:6a:7e > 00:1f:12:14:e6:36, ethertype IPv4 (0x0800), length 212: x.x.x.x.60863 > 195.82.146.114.80: P 1:159(158) ack 1 win 5840
12:53:32.486757 00:1f:12:14:e6:36 > 00:15:17:ab:6a:7e, ethertype IPv4 (0x0800), length 60: 195.82.146.114.80 > x.x.x.x.60863: . ack 159 win 6432
12:53:32.487048 00:1f:12:14:e6:36 > 00:15:17:ab:6a:7e, ethertype IPv4 (0x0800), length 833: 195.82.146.114.80 > x.x.x.x.60863: P 1:780(779) ack 159 win 6432
12:53:32.489188 00:15:17:ab:6a:7e > 00:1f:12:14:e6:36, ethertype IPv4 (0x0800), length 54: x.x.x.x.60863 > 195.82.146.114.80: . ack 780 win 7011
12:53:33.490568 00:15:17:ab:6a:7e > 00:1f:12:14:e6:36, ethertype IPv4 (0x0800), length 259: x.x.x.x.60863 > 195.82.146.114.80: P 159:364(205) ack 780 win 7011
12:53:33.623224 00:1f:12:14:e6:36 > 00:15:17:ab:6a:7e, ethertype IPv4 (0x0800), length 1506: 195.82.146.114.80 > x.x.x.x.60863: . 780:2232(1452) ack 364 win 7504
12:53:33.623268 00:1f:12:14:e6:36 > 00:15:17:ab:6a:7e, ethertype IPv4 (0x0800), length 1506: 195.82.146.114.80 > x.x.x.x.60863: . 2232:3684(1452) ack 364 win 7504
12:53:33.623854 00:15:17:ab:6a:7e > 00:1f:12:14:e6:36, ethertype IPv4 (0x0800), length 590: y.y.y.y > 195.82.146.114: ICMP x.x.x.x unreachable - need to frag (mtu 1480), length 556
12:53:33.623860 00:15:17:ab:6a:7e > 00:1f:12:14:e6:36, ethertype IPv4 (0x0800), length 590: y.y.y.y > 195.82.146.114: ICMP x.x.x.x unreachable - need to frag (mtu 1480), length 556
12:53:33.884220 00:15:17:ab:6a:7e > 00:1f:12:14:e6:36, ethertype IPv4 (0x0800), length 259: x.x.x.x.60863 > 195.82.146.114.80: P 159:364(205) ack 780 win 7011
12:53:34.013850 00:1f:12:14:e6:36 > 00:15:17:ab:6a:7e, ethertype IPv4 (0x0800), length 60: 195.82.146.114.80 > x.x.x.x.60863: . ack 364 win 7504
12:53:34.018615 00:1f:12:14:e6:36 > 00:15:17:ab:6a:7e, ethertype IPv4 (0x0800), length 1506: 195.82.146.114.80 > x.x.x.x.60863: . 780:2232(1452) ack 364 win 7504
12:53:34.019080 00:15:17:ab:6a:7e > 00:1f:12:14:e6:36, ethertype IPv4 (0x0800), length 590: y.y.y.y > 195.82.146.114: ICMP x.x.x.x unreachable - need to frag (mtu 1480), length 556
12:53:34.810497 00:1f:12:14:e6:36 > 00:15:17:ab:6a:7e, ethertype IPv4 (0x0800), length 1506: 195.82.146.114.80 > x.x.x.x.60863: . 780:2232(1452) ack 364 win 7504
12:53:34.810919 00:15:17:ab:6a:7e > 00:1f:12:14:e6:36, ethertype IPv4 (0x0800), length 590: y.y.y.y > 195.82.146.114: ICMP x.x.x.x unreachable - need to frag (mtu 1480), length 556
почему они упорно шлют размер 1506, хотя запрашиваем 1480?