Here is what my Network looks like,
LTE Modem -> Switch -> [VLAN #2] -> lte-vlan interface
Wifi AP ----------^ -> [VLAN #1] -> 2f-switch interface
Switch tags the traffic with VLAN Tags.
The LTE modem is, Huawei 5G CPE Pro and I am using Airtel LTE.
I have confirmed with `ping -M do -c 1330 <ip>` and from the LTE interface stats on my phone that Airtel is using 1358 as the MTU value.
I have configured 1500 L3 MTU on lte-vlan interface & 1594(4 bytes for vlan tag) L2 MTU.
The issue I am seeing is, HTTP Requests to some sites like Google work fine but requests to any other sites get stuck at `SYN_SENT` stage in the TCP handshake. ICMP is working perfectly fine.
I have already checked nearly a dozen threads in the forum where people have had similar issues and I asked on Mikrotik IRC, Everything seems to be pointing to a MTU issue.
Someone on IRC suggested I try clamping the MTU to MSS and I also found that exact suggestion in pretty much all the threads here so I added a rule like,
but I haven't _really_ had success with it. Traffic is still getting stuck at SYN_SENT stage. I am not sure what else to try to debug/fix this problem and I have not found any other suggestions either so, Any help here is much appreciated.
Code: Select all
/ip firewall mangle add chain=forward action=change-mss new-mss=clamp-to-pmtu passthrough=yes tcp-flags=syn protocol=tcp out-interface=lte-vlan log=no log-prefix="change-mss"