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Old 09-11-2014, 03:35 PM   #1
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Registered: Sep 2014
Posts: 2

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Corrupted MAC on input error while logged on an Open Swan VPN

Hello, this is my first post here so apologies in advance if there's lack of data or formatting, i'll do my best.

So the issue is the following: I have several Ubuntu servers running on a AWS environment and i have installed one with Open Swan so other users may login into them via VPN (using ssh from their laptops, most of them are Airbooks)

One issue i have noted is that while they are logged via VPN and run a command that has a lot of output (like a find /), the screen will eventually show:

Corrupted MAC on input.
Disconnecting: Packet corrupt
And then it will drop the ssh connection. This is not totally preventing them to do their jobs, but it is fairly annoying. As an additional data, i have logged in into the servers through an external/elastic IP instead of the VPN and i'm able to see all the output of all commands (also, the connection/response seems faster at this way).

I have checked a few forums in which they have talked about Checksum Offloading but i'm not sure if it will apply in this case. Please let me know if you need further information to help me on this matter.


Last edited by nbriozzo; 09-11-2014 at 03:37 PM.
Old 09-11-2014, 08:39 PM   #2
Registered: Mar 2008
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Thought I was right. checksum offload in nic causes a bogus mac. While checksum offload is great for reducing cpu load it also causes an oddity. It forces a mac to the host since all the work was really done in nic. Wireshark will also show this oddity.
Old 09-12-2014, 12:11 PM   #3
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Registered: Sep 2014
Posts: 2

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root@server$ethtool --show-offload eth0
Offload parameters for eth0:
rx-checksumming: off
tx-checksumming: off
scatter-gather: off
tcp-segmentation-offload: off
udp-fragmentation-offload: off
generic-segmentation-offload: off
generic-receive-offload: off
large-receive-offload: off
rx-vlan-offload: off
tx-vlan-offload: off
ntuple-filters: off
receive-hashing: off

This is the VPN server where i get the IP. I've run commands to disable checksum, but i still get the "Corrupted MAC on input, Disconnecting: Packet corrupt" error.


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