Packet loss when connecting via IPv6

David Woodhouse dwmw2 at
Wed Jan 27 17:04:24 PST 2016

On Thu, 2016-01-28 at 02:02 +0100, Johannes Brechtmann wrote:
> When connecting to a vpn server via IPv6, I get only small packets (I
> guess), so ping works fine, http redirects work but http 200 responses
> get lost. With ssh I can log into a server and use basic commands like
> uptime but e.g. top doesn't work.
> If I connect to the server via IPv4 everything works fine.
> If I connect to the same server with the Cisco AnyConnect client (no
> matter if IPv6 or IPv4), everything works fine, too. 
> I'm using openconnect v7.06 on Debian testing and openconnect for
> android v1.11.
> I'm wondering if this is a problem of openconnect or the server I try
> to connect to.
> Can anyone confirm or deny this behaviour with any vpn server?

What MTU does the AnyConnect client set for the IPv6 link. And what MTU
does OpenConnect set?

David Woodhouse                            Open Source Technology Centre
David.Woodhouse at                              Intel Corporation

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