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I'm using a RUTX09 and RUTX11 and i'm looking to configure them in bridge mode.

It seems that when enabling bridge mode, the RUTX is adjusting the MTU value for the LTE interface. NAT mode does not adjust the MTU.

This results in weird things that must be corrected on other devices (like a firewall) when configuring RUTX in bridge mode.

Can someone explain why MTU is changed from 1500 to 1460 when bridge mode is enabled?

Mon Mar 16 10:51:45 2020 daemon.notice netifd: Interface 'mob1s1a1' is setting up now
Mon Mar 16 10:51:45 2020 daemon.notice netifd: mob1s1a1 (9965): wwan[9965] Using proto:GobiNet device:wwan0 iface:wwan0 desc:Quectel EG06
Mon Mar 16 10:51:50 2020 daemon.notice netifd: mob1s1a1 (9965): Quering active sim position
Mon Mar 16 10:51:50 2020 daemon.notice netifd: mob1s1a1 (9965): OK
Mon Mar 16 10:51:50 2020 daemon.notice netifd: mob1s1a1 (9965): Checking modem status
Mon Mar 16 10:51:50 2020 daemon.notice netifd: mob1s1a1 (9965): PIN is verified or PIN verification is disabled
Mon Mar 16 10:51:50 2020 daemon.notice netifd: mob1s1a1 (9965): Setting up
Mon Mar 16 10:51:50 2020 daemon.notice netifd: mob1s1a1 (9965): Clearing pdp context
Mon Mar 16 10:51:50 2020 daemon.notice netifd: mob1s1a1 (9965): OK
Mon Mar 16 10:51:50 2020 daemon.notice netifd: mob1s1a1 (9965): Starting connection manager
Mon Mar 16 10:51:50 2020 daemon.notice netifd: mob1s1a1 (10583): [03-16_10:51:50:509] WCDMA&LTE_QConnectManager_Linux&Android_V1.1.38
Mon Mar 16 10:51:51 2020 daemon.notice netifd: mob1s1a1 (10583): [03-16_10:51:50:509] /usr/sbin/quectel-CM profile[1] = (null)/(null)/(null)/0, pincode = (null), config = mob1s1a1
Mon Mar 16 10:51:51 2020 daemon.notice netifd: mob1s1a1 (10583): [03-16_10:51:50:512] Find /sys/bus/usb/devices/3-1 idVendor=2c7c idProduct=0306
Mon Mar 16 10:51:51 2020 daemon.notice netifd: mob1s1a1 (10583): [03-16_10:51:50:513] Find /sys/bus/usb/devices/3-1:1.4/net/wwan0
Mon Mar 16 10:51:51 2020 daemon.notice netifd: mob1s1a1 (10583): [03-16_10:51:50:513] Find usbnet_adapter = wwan0
Mon Mar 16 10:51:51 2020 daemon.notice netifd: mob1s1a1 (10583): [03-16_10:51:50:513] Find /sys/bus/usb/devices/3-1:1.4/GobiQMI/qcqmi0
Mon Mar 16 10:51:51 2020 daemon.notice netifd: mob1s1a1 (10583): [03-16_10:51:50:513] Find qmichannel = /dev/qcqmi0
Mon Mar 16 10:51:51 2020 daemon.notice netifd: mob1s1a1 (10583): [03-16_10:51:50:514] Find qmapnet_adapter = wwan0.1
Mon Mar 16 10:51:51 2020 daemon.notice netifd: mob1s1a1 (10583): [03-16_10:51:50:520] Get clientWDS = 7
Mon Mar 16 10:51:51 2020 daemon.notice netifd: mob1s1a1 (10583): [03-16_10:51:50:584] Get clientDMS = 8
Mon Mar 16 10:51:51 2020 daemon.notice netifd: mob1s1a1 (10583): [03-16_10:51:50:648] Get clientNAS = 9
Mon Mar 16 10:51:51 2020 daemon.notice netifd: mob1s1a1 (10583): [03-16_10:51:50:712] Get clientUIM = 10
Mon Mar 16 10:51:51 2020 daemon.notice netifd: mob1s1a1 (10583): [03-16_10:51:50:776] requestBaseBandVersion EG06ELAR03A05M4G
Mon Mar 16 10:51:51 2020 daemon.notice netifd: mob1s1a1 (10583): [03-16_10:51:50:968] requestGetSIMStatus SIMStatus: SIM_READY
Mon Mar 16 10:51:51 2020 daemon.notice netifd: mob1s1a1 (10583): [03-16_10:51:51:032] requestGetProfile[1] ///0
Mon Mar 16 10:51:51 2020 daemon.notice netifd: mob1s1a1 (10583): [03-16_10:51:51:096] requestRegistrationState2 MCC: 204, MNC: 16, PS: Attached, DataCap: LTE
Mon Mar 16 10:51:51 2020 daemon.notice netifd: mob1s1a1 (10583): [03-16_10:51:51:160] requestQueryDataCall IPv4ConnectionStatus: DISCONNECTED
Mon Mar 16 10:51:51 2020 daemon.notice netifd: mob1s1a1 (10583): [03-16_10:51:51:288] requestRegistrationState2 MCC: 204, MNC: 16, PS: Attached, DataCap: LTE
Mon Mar 16 10:51:51 2020 daemon.notice netifd: mob1s1a1 (10583): [03-16_10:51:51:352] requestSetupDataCall WdsConnectionIPv4Handle: 0xc4c5d600
Mon Mar 16 10:51:51 2020 daemon.notice netifd: Interface 'mob1s1a1' is now up
Mon Mar 16 10:51:51 2020 daemon.info ledman: Interface `mob1s1a1` state changed to up
Mon Mar 16 10:51:52 2020 daemon.notice netifd: mob1s1a1 (10583): [03-16_10:51:51:480] requestQueryDataCall IPv4ConnectionStatus: CONNECTED
Mon Mar 16 10:51:52 2020 daemon.notice netifd: mob1s1a1 (10583): [03-16_10:51:51:544] change mtu 1500 -> 1460
Mon Mar 16 10:51:52 2020 daemon.notice netifd: mob1s1a1 (10583): [03-16_10:51:51:545] /lib/netifd/mobile.script up wwan0.1 mob1s1a1

1 Answer

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Hello,

It could be that operator selects what MTU will be, can you please PM me with the troubleshoot file (System -> Administration -> Troubleshoot) when you set Bridge mode on RUTX11.

And could you please let us know what kind of issue does MTU changes aplly to your solution?

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i'm not sure if i understand your question. I assume you're asking what issues i'm seeing when this MTU change occurs?

Because of the MTU change, i have TLS handshake problems (websites using https do not work, so pretty much the internet) when browsing the web on a clientdevice behind the firewall that gets the public IP bridged by the RUTX. I needed to lower the MTU/MSS-clamping setting on my firewall to be able to browse the internet properly.

I do not have these problems when using NAT mode.