Поменял прошивку на 
http://ftp.dlink.ru/pub/Router/DIR-825/ ... Beta06.bin . MTU  пробовал разные значения 1300,1280, сейчас стоит 1100. Отключил SPI, в разделе QoS Engine снял галочку напротив пункта Automatic Uplink Speed. Через несколько секунд пропадает ping между компьютером и роутером, а токже ping с интернетом.
Dec 13 14:31:55	 info	  read /etc/hosts - 1 addresses
Dec 13 14:31:55	 info	  using nameserver 192.168.2.20#53
Dec 13 14:31:55	 info	  using nameserver 192.168.2.90#53
Dec 13 14:31:55	 info	  reading /etc/resolv.conf
Dec 13 14:31:55	 info	  compile time options: IPv6 GNU-getopt no-ISC-leasefile no-DBus no-I18N no-TFTP
Dec 13 14:31:55	 info	  started, version 2.41 cachesize 150
Dec 13 14:31:53	 info	  exiting on receipt of SIGTERM
Dec 13 14:31:52	 notice	  pppd sent restart signal to rc 
Dec 13 14:31:52	 notice	  pppd check for rc to be idle ? 
Dec 13 14:31:52	 notice	  ipcp_up: remote PPP IP address 172.16.0.1
Dec 13 14:31:52	 notice	  ipcp_up: local PPP IP address 62.140.234.39
Dec 13 14:31:52	 notice	  ipcp_up: Open /var/tmp/pptp_server_ip.txt (l2tp_server_ip.txt) fail or Using PPPoE
Dec 13 14:31:52	 info	  CHAP authentication succeeded
Dec 13 14:31:51	 notice	  Connect: ppp0 '--' /dev/pts/0
Dec 13 14:31:51	 info	  Using interface ppp0
Dec 13 14:31:51	 notice	  pppd 2.4.3 started by root, uid 0
Dec 13 14:31:34	 info	  using nameserver 192.168.2.20#53
Dec 13 14:31:34	 info	  using nameserver 192.168.2.90#53
Dec 13 14:31:34	 info	  reading /etc/resolv.conf
Dec 13 14:28:04	 info	  Die Exit.
Dec 13 14:28:04	 notice	  ppp auth: Connection terminated.
Dec 13 14:28:04	 info	  Sent 46434 bytes, received 271479 bytes.
Dec 13 14:28:04	 info	  Connect time 4.7 minutes.
Dec 13 14:28:04	 info	  Terminating on signal 15
Dec 13 14:23:26	 info	  read /etc/hosts - 1 addresses
Dec 13 14:23:26	 info	  using nameserver 192.168.2.20#53
Dec 13 14:23:26	 info	  using nameserver 192.168.2.90#53
Dec 13 14:23:26	 info	  reading /etc/resolv.conf
Dec 13 14:23:26	 info	  compile time options: IPv6 GNU-getopt no-ISC-leasefile no-DBus no-I18N no-TFTP
Dec 13 14:23:26	 info	  started, version 2.41 cachesize 150
Dec 13 14:23:26	 info	  UDHCPD sending OFFER of 192.168.0.100
Dec 13 14:23:25	 info	  exiting on receipt of SIGTERM
Dec 13 14:23:24	 notice	  pppd sent restart signal to rc 
Dec 13 14:23:24	 notice	  pppd check for rc to be idle ? 
Dec 13 14:23:24	 notice	  ipcp_up: remote PPP IP address 172.16.0.1
Dec 13 14:23:24	 notice	  ipcp_up: local PPP IP address 62.140.234.39
Dec 13 14:23:24	 notice	  ipcp_up: Open /var/tmp/pptp_server_ip.txt (l2tp_server_ip.txt) fail or Using PPPoE
Dec 13 14:23:24	 info	  CHAP authentication succeeded
Dec 13 14:23:23	 notice	  Connect: ppp0 '--' /dev/pts/0
Dec 13 14:23:23	 info	  Using interface ppp0
Dec 13 14:23:23	 notice	  pppd 2.4.3 started by root, uid 0
Dec 13 14:23:21	 info	  using nameserver 192.168.2.20#53
Dec 13 14:23:21	 info	  using nameserver 192.168.2.90#53
Dec 13 14:23:21	 info	  reading /etc/resolv.conf
Dec 13 14:23:16	 info	  read /etc/hosts - 1 addresses
Dec 13 14:23:16	 info	  using nameserver 192.168.2.20#53
Dec 13 14:23:16	 info	  using nameserver 192.168.2.90#53
Dec 13 14:23:16	 info	  reading /etc/resolv.conf
Dec 13 14:23:16	 info	  compile time options: IPv6 GNU-getopt no-ISC-leasefile no-DBus no-I18N no-TFTP
Dec 13 14:23:16	 info	  started, version 2.41 cachesize 150
Dec 13 14:23:07	 info	  device_lan_ip=192.168.0.1 , device_lan_subnet_mask=255.255.255.0
Dec 13 14:23:07	 info	  DHCP server start.
Dec 13 14:23:01	 info	  [Initialized, firmware version: 2.05WW ]  
Dec 13 14:23:00	 notice	  0x00660000-0x00670000 :  caldata 
Dec 13 14:23:00	 notice	  0x00000000-0x00040000 :  uboot 
Dec 13 14:23:00	 notice	  klogd started: BusyBox v1.01 (2011.12.13-06:27+0000)