Opened 3 years ago

#18121 new defect

Cannot set mtu to 1500 for a 3g-stick pppd connection

Reported by: Vittorio G (VittGam) <openwrt@…> Owned by: developers
Priority: normal Milestone: Barrier Breaker 14.07
Component: packages Version: Barrier Breaker 14.07
Keywords: pppd, comgt Cc:



I'm using Barrier Breaker r42853.

With a Huawei internet key and this config:

config interface 'wwan'
        option proto '3g'
        option device '/dev/ttyUSB0'
        option service 'umts_only'
        option pincode '1234'
        option apn 'my.apn'
        option defaultroute '1'
        option peerdns '0'
        option dns ''
        option mtu '1500'
        option ipv6 '0'
        option metric '2'

The mtu on 3g-wwan is stuck at 1440.

A workaround is this script (with the exec bit set):

root@router12:~# cat /etc/ppp/ip-up.d/fix-mtu-1500
[ "$IFNAME" = "3g-wwan" ] && ifconfig "$IFNAME" mtu 1500

The interface is then able to use 1500-byte packets correctly.

Vittorio G

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