By EnisK
I have encountered network issues (documents are printing multiple time by chance) while cups printing from a Digitalocean server (CentOS) to a external printer. Doing a network analysis with Wireshark I saw that by chance packages are retransmitted to the print server and so documents are printed 2 or 3 times.
I have a server at an other cloud provider and with that I don’t have that problems.
A netstat -s for the digital ocean server shows:
netstat -s | grep retr
650374 segments retransmited
1 times recovered from packet loss due to fast retransmit
1 timeouts after reno fast retransmit
44015 fast retransmits
5833 forward retransmits
4373 retransmits in slow start
1 classic Reno fast retransmits failed
1428 SACK retransmits failed
For the other cloud provider it shows
netstat -s | grep retr
8389033 segments retransmited
73 times recovered from packet loss due to fast retransmit
16 timeouts after reno fast retransmit
54023 fast retransmits
3285 forward retransmits
8724 retransmits in slow start
37 classic Reno fast retransmits failed
1732 SACK retransmits failed
The number of retransmissions on the digitalocean server is significant higher than on the other cloud server from a other cloud provider - although the other cloud server has much more load and much more network traffic.
Does anyone have an idea what could be the reason for that?
Thanks for any help.
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Hi there,
The high number of TCP retransmissions could be due to a number of reasons, ranging from network congestion, packet loss, or even an issue with the TCP/IP stack configuration on your DigitalOcean server. Here are a few steps you could take to further diagnose and possibly resolve the issue:
-
Check for network congestion: Network congestion could be causing the retransmissions. You could use network monitoring tools like
iftop,nload, ornetstatto check for high network usage. Additionally, check if there’s any pattern to the retransmissions - do they occur at specific times of the day or when specific tasks are running? -
Packet loss: Packet loss could be another cause. You could use
mtr,ping, ortracerouteto check for packet loss between your DigitalOcean server and the printer. -
Check TCP/IP stack configuration: Check the TCP/IP stack configuration on your DigitalOcean server. Use the
sysctlcommand to check for settings that might be causing the issue. For example, you could checknet.ipv4.tcp_retries2, which controls the number of times TCP will attempt to retransmit a packet before giving up. -
Check server resources: Check if your DigitalOcean server has sufficient CPU and memory resources. High server load could cause delays in processing network packets, leading to retransmissions.
-
Firewall or security groups: Check the firewall or security group rules on your DigitalOcean server. Misconfigured rules could be interfering with TCP traffic.
-
Contact DigitalOcean support: If you’re unable to diagnose the issue yourself, consider reaching out to DigitalOcean support. They might have insight into whether there’s an issue with the underlying network infrastructure.
Another option that you could consider is using a CDN like CloudFlare, they also offer free DDoS protection so that any suspicious requests will be filtered out before they reach your server.
Best,
Bobby
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