Zyxel MTU

ZyXEL routers. How do I change its MTU?

On Newer Zyxel Routers
Telnet to the Router by doing this:

Go to Start/Run…
type telnet 192.168.0.1
click OK button
Now enter your password… (the original is 1234). You will get a menu.

Go to menu 24.8 (type 24 Enter 8 Enter). This brings command line interface.
At command prompt type the following command followed by Enter:

ip adj wanif0 1300

This will lower the current MTU limit to 1300.

On Older Zyxel Routers :

telnet 192.168.0.1
Now enter your password

At the command Prompt :

eg. for MTU=1452
!
ras> ip ifconfig wanif0 xxx.xxx.xxx.xxx mtu 1400
ras> ip ifconfig enif0 xxx.xxx.xxx.xxx mtu 1400

where xxx.xxx.xxx.xxx is your current ip address which is the ‘inet’ field when you type

ras> ip ifconfig wanif0
ras> ip ifconfig enif0

This will lower the current MTU limit to 1400.
You can also add the above command into sys file in order to save settings on reboot of router :
!
sys edit autoexec.net
!
wan atm vc webRedirDis 1
sys errctl 0
ip ifconfig enif0 192.168.1.1 mtu 1400
sys trcl level 5
sys trcl type 1180
sys trcp cr 64 96
sys trcl sw off
sys trcp sw off
ip tcp mss 512
ip tcp limit 2
ip tcp irtt 65000
ip tcp window 2
ip tcp ceiling 6000
ip rip activate
ip rip merge on
ppp ipcp compress off
sys wdog sw on
ip icmp discovery enif0 off
bridge mode 1
sys quick enable
ether driver qroute 2
wan adsl rateadap on
wan adsl targetnoise 0x06
wan adsl driver dnmaxbits 10
EOF