# I can ping through the tunnel, but any real work causes it to lock up. Is this an MTU problem?

Probably. It's best to change the `mssfix` parameter rather than directly changing the MTU of the TUN/TAP adapter. For example:

```
mssfix 1200
```

You could also combine this with:

```
fragment 1200
```

Note however that `fragment` will exact a performance penalty.

Common values to try for `mssfix`/`fragment`: 1200, 1300, or 1400.

Note that while `mssfix` only needs to be specified on one side of the connection, `fragment` should be specified on both.