compiz: missing key 1F87540B4A729399

W: GPG-Fehler: stretch InRelease: Die folgenden Signaturen konnten nicht überprüft werden, weil ihr öffentlicher Schlüssel nicht verfügbar ist: NO_PUBKEY 1F87540B4A729399

gpg --import ./
gpg --export 1F87540B4A729399 | apt-key add -
apt-get update

analyze packet loss with wireshark

Lost packets can extremely slow down a network and even completely bring down at high load.

Poorly laid cables, network segments that are too long (above but also below 100 meters) but also too many switches can cause the network to become out of sync.

With Wireshark you can easily test your own connection for lost packet segments and retransmissions:

  • tcp.analysis.lost_segment – Indicates we’ve seen a gap in sequence numbers in the capture. Packet loss can lead to duplicate ACKs, which leads to retransmissions.
  • tcp.analysis.retransmission – Displays all retransmissions in the capture. A few retransmissions are OK, excessive retransmissions are bad. This usually shows up as slow application performance and/or packet loss to the user.

some lost segments to web destinations are ok, but massive lost packets on connections to a local server are bad.