Re: Cable modem packet loss?

[Alex <mysqlstudent@xxxxxxxxx>]

Hi,

Doing a bit more searching, I've located this from nearly 10 years ago that describes my problem exactly:

https://hardforum.com/threads/linux-network-bridge-dropping-rx-packets.1788469/

I've confirmed that ipv6 isn't disabled:

sysctl -a|grep ipv6|grep disable
net.ipv6.conf.all.disable_ipv6 = 0
net.ipv6.conf.all.disable_policy = 0
net.ipv6.conf.br0.disable_ipv6 = 0
net.ipv6.conf.br0.disable_policy = 0
net.ipv6.conf.default.disable_ipv6 = 0
net.ipv6.conf.default.disable_policy = 0
net.ipv6.conf.enp4s0.disable_ipv6 = 0
net.ipv6.conf.enp4s0.disable_policy = 0
net.ipv6.conf.eth0.disable_ipv6 = 0
net.ipv6.conf.eth0.disable_policy = 0
net.ipv6.conf.lo.disable_ipv6 = 0
net.ipv6.conf.lo.disable_policy = 0

Equally interesting is that this problem doesn't happen when tcpdump is running. I've also disabled my iptables packet filter and it still happens.

Any ideas greatly appreciated.

On Sat, Jun 3, 2023 at 9:46 AM Alex <mysqlstudent@xxxxxxxxx> wrote:

Hi,

I have an E3-1240 fedora37 postfix system using SSDs connected to a cable modem that's having problems with dropped packets. There is one other fedora37 server (E5-1650) directly connected to the cable modem that is not having the same problem, although it's just routing packets, not really doing much processing of data. The server with the problem is using libreswan to create a VPN between itself and an i7-7700K with fedora37 managed at OVH, thinking it would be more resilient than the cable connection itself. The problem also happens without the VPN, but perhaps not to the same degree.

I think the server is certainly powerful enough to process the amount of DNS queries, but there's also a lot of timeouts.

How do I troubleshoot this? It's the bridge experiencing the dropped packets, not the interface itself, it seems?

They're not packet errors - just dropped packets. Perhaps the processor can't handle the traffic? 

Do you have a server connected to a cable modem? Is there something about it being a cable connection that could be causing this?

There's about 27k dropped packets in about 12 hours of uptime.

br0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 68.195.111.45  netmask 255.255.255.248  broadcast 68.195.111.47
        ether ae:64:2c:25:b5:44  txqueuelen 1000  (Ethernet)
        RX packets 11355786  bytes 21634260431 (20.1 GiB)
        RX errors 0  dropped 26349  overruns 0  frame 0
        TX packets 7374430  bytes 993860294 (947.8 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        ether 14:da:e9:97:ab:72  txqueuelen 1000  (Ethernet)
        RX packets 16224042  bytes 22179550934 (20.6 GiB)
        RX errors 0  dropped 165  overruns 0  frame 0
        TX packets 7493927  bytes 1031987928 (984.1 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
        device interrupt 17  memory 0xdf100000-df120000  

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