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Old 03-01-2018, 05:04 PM   #1
Registered: Oct 2005
Location: localhost.localdomain
Distribution: CentOS
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Centos7 NIC packet drop


I have a very strange problem I can't find a solution for.

The story is like this. I had an Amazon ec2 instance that I needed to migrate to a guest VPS running on Hyper-V server. So save time I simply performed a raw copy of the whole filesystem from the ec2 instance to the Hyper-V VPS. So then I updated the networking, fstab and kernel config so it boots properly.

Now after doing so I found that the network interface shows constant packet drops. I have installed munin and netdata and it shows 1-2 packets/s being dropped.

Below is output from ifconfig:
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet  netmask  broadcast
        ether 00:15:5d:00:1b:18  txqueuelen 1000  (Ethernet)
        RX packets 262  bytes 27971 (27.3 KiB)
        RX errors 0  dropped 168  overruns 0  frame 0
        TX packets 87  bytes 12146 (11.8 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
So this increases constantly without stopping. Now I checked a lot of things, routing, packet buffer stuff and nothing helped to solve the problem.

Further more I have added a second NIC to the VPS and when started it drops packets right away without even having a valid IP assigned with connection to internet.

Can anyone please help me find a solution to this problem? What can be causing the constant packet drop?

Many thanks in advance.
Old 03-03-2018, 10:38 AM   #2
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Have you verified the Hypervisor's NIC itself is not what is dropping packets? It seems unlikely a virtual's NIC itself would do that.

I can say that RHEL7 (and therefore CentOS7) run under MS HyperV for me without dropping packets. In general any networking issues I've seen on Linux guests under Hyper-V turned out to be issues with the physical server itself (e.g. failing NIC or loose NIC cable - sometimes just recrimping the latter helps).

What you did though doesn't sound valid to me. The guest OS is built for the platform it lives on so just copying files from Amazon EC2 to Hyper-V wouldn't be appropriate. In fact I found this links that shows you can export a VHD for Hyper-V from Amazon. (Note I've not done this myself.)

If the issue isn't the Hypervisor's networking and you can't do the steps in above links what you might want to try doing is a new Linux guest install on the Hyper-V (not a copy) then copy in relevant files from your other guest to that but specifically excluding "system" files. i.e. Just copy over the applications you need.

Last edited by MensaWater; 03-03-2018 at 10:39 AM.


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