# Determine ideal MTU without ping?

## grant123

I'm currently connecting to the internet by tethering to my cell phone.  I'd like to determine my ideal MTU but from what I understand this is done via pings and I get 100% packet loss when pinging so my ISP must be dropping them.  Is there anything else I can do to figure this out?

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## PaulBredbury

You didn't mention who you're trying to ping. Try e.g.:

```
ping -s 1464 -M do www.dslreports.com
```

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## Hu

With the right configuration, PMTUD should handle this for you.  Have you disabled PMTUD?

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## grant123

PaulBredbury, I lose all of those pings unfortunately.

Hu, how is PMTUD enabled/disabled on Gentoo?

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## massimo

 *grant123 wrote:*   

> PaulBredbury, I lose all of those pings unfortunately.
> 
> Hu, how is PMTUD enabled/disabled on Gentoo?

 

disable pmtu discovery

```
sysctl -w ip_no_pmtu_disc=1
```

enable pmtu discovery

```
sysctl -w ip_no_pmtu_disc=0
```

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## grant123

Thank you!

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