NymVPN sets the MTU automatically per platform and mode, within a range of 1280 to 1500 bytes. There is nothing you need to configure: the values are chosen to avoid packet fragmentation while staying compatible with IPv6 and cellular networks.
What is the MTU and why does it matter?
The MTU (Maximum Transmission Unit) is the largest packet size a network connection can transmit without splitting it into fragments. If the MTU is set too high for the path your traffic takes, packets get fragmented or dropped, which shows up as slow speeds, stalling uploads, or sites that never finish loading. Set too low, and you waste capacity on overhead.
VPNs always need a lower MTU than a bare connection because each layer of encryption adds headers to every packet. NymVPN's Fast mode uses a 2-hop tunnel-in-a-tunnel WireGuard design, so the overhead of both tunnels has to fit inside every packet. See How does NymVPN implement WireGuard? for how that design works.
MTU values in Fast mode
- Mobile (Android and iOS): 1280 bytes. This is the IPv6 minimum, chosen for maximum compatibility with cellular networks after subtracting the overhead of both encryption layers.
- Desktop (Windows, macOS, Linux): 1340 bytes. Desktop network paths tolerate slightly larger packets, so the MTU is raised while still accounting for the doubled headers.
MTU values in Anonymous mode
- Mobile: 1280 bytes, for the same compatibility reasons as Fast mode.
- Desktop: 1500 bytes, the standard Ethernet maximum, for best throughput on the mixnet.
Related questions
Can I change the MTU myself?
The NymVPN apps manage the MTU automatically and do not expose a setting for it. The values above are tuned per platform so manual adjustment is not needed.
Could the MTU explain my slow connection?
Usually not, since the values are conservative by design. Slow connections are more often related to server selection, network conditions, or mode choice. See Why do I experience slow speeds on NymVPN? and How do I test the VPN speed and performance?
Why is mobile lower than desktop?
Cellular networks and IPv6 transit are stricter about packet sizes. 1280 bytes is the minimum MTU every IPv6 link must support, which makes it the safest choice on mobile.