The MTU parameter problem can not access the external network website

Publication Date:  2012-11-27 Views:  178 Downloads:  0
Issue Description
Customers use our products USG2120, it connected with 10MBPS network of BSNL (broadband carrier in India) through ADSL interface, after it configured the Dialer, NAT, VLANIF, DNS information, PC can ping www.yahoo.com www.yahoo.com in network, but it can not open the web site page.
Alarm Information
NULL
Handling Process
It recommends that customers change every VLANIF interface MTU of 1400, as follows:
#
interface Vlanif1
mtu 1400
ip address 192.168.120.1 255.255.255.0
#
interface Vlanif2
mtu 1400
ip address 192.168.121.1 255.255.255.0
#
interface Vlanif3
mtu 1400
ip address 192.168.122.1 255.255.255.0
#
interface Vlanif4
mtu 1400
ip address 192.168.123.1 255.255.255.0
#
interface Vlanif5
mtu 1400
ip address 192.168.124.1 255.255.255.0
#
interface Vlanif6
mtu 1400
ip address 192.168.125.1 255.255.255.0
#
interface Vlanif7
mtu 1400
ip address 192.168.126.1 255.255.255.0
#
interface Vlanif8
mtu 1400
ip address 192.168.127.1 255.255.255.0
#
Root Cause
By analysis of customer provides configuration script file, the basic configuration is correct, no problem Dialer, NAT, the VLANIF, DNS, and routing information, and validated within the network, a PC can ping the external network, but can not open the page. our equipment replaced peer vendor  Wireless N-Router, after Model No WRX150 router, customers intranet PC can access external sites. In this case, under normal circumstances, need to check both ends of the link's configuration parameters. Therefore customers provide WRX150 configuration information, as follows:
PPPOE advance setting of MTU Setting as 1400 and DNS
218.248.255.212
218.248.255.139

Thus, we doubt that the MTU parameter is problematic, because our equipment each interface MTU default parameters is 1500 bytes. Both ends (USG212O the BSNL devices) MTU parameters are inconsistent, leading to both link negotiation can not complete the normal connection. Furthermore, ADSL using PPPoE slightly less than this value, typically 1492. The customers need to use the MTU is 1400 bytes.
Suggestions
It comes to this kind of problem, priority check whether equipment is configured DNS information, and then check the link interconnection configuration information; validation testing with other equipment replacement, is also a good choice, conducive to the problem of rapid finding.

END