>I don't have any authoritative thoughts on why TCP would work when UDP
doesn't, but one thing that comes to mind is MTU size. If the MTU size was
too large, UDP will simply fail. TCP *should* [but may not always] get a
fragmentation notification telling the sender to fragment the packets down
to fit through a smaller than expected MTU in the connection.
Make sense.
Try to add following options to both sides:
mssfix 1200 ##### tell up-level tcp to not send a packet larger
than 1200,this only works for tcpfragment 1200 ##### fragment a
packet if it is larger than 1200,this works for udp/icmp(also works
for tcp if 'mssfix' is not set,but not as efficient as 'mssfix')
On Mon, Sep 4, 2017 at 9:13 AM, Gregory Sloop <gr...@sloop.net> wrote:
> Top Posting:
>
> UDP is preferred vs TCP because of TCP inside TCP issues - e.g. TCP
> sliding window ACK inside another TCP sliding window ACK. As packet loss
> increases, this becomes a huge problem. Essentailly, you have TCP stream
> inside the OVPN tunnel, and it's being ferried to the remote site/client.
> And the outside tunnel is also a TCP connection. All the "benefits" of TCP
> connections, essentially can become problems with having a TCP inside TCP
> conntection.
>
> Rather than rehash it all - here's a decent link that describes some of
> the problems:
> http://sites.inka.de/bigred/devel/tcp-tcp.html
>
> I don't have any authoritative thoughts on why TCP would work when UDP
> doesn't, but one thing that comes to mind is MTU size. If the MTU size was
> too large, UDP will simply fail. TCP *should* [but may not always] get a
> fragmentation notification telling the sender to fragment the packets down
> to fit through a smaller than expected MTU in the connection.
>
> Do some searches on MTU/MSS and see if you can determine if your pathway
> has a smaller than expected MTU. PPPoE is one specific case where MTU's are
> smaller because of the PPPoE overhead.
>
> Some good reading re: MTU/MSS. [Not carefully vetted, just quick perusal
> seems to indicate they might be useful reading.]
> https://supportforums.cisco.com/t5/lan-switching-and-
> routing/mtu-mss-and-tcp-window-size/td-p/2966099
> https://learningnetwork.cisco.com/thread/91863
>
> -Greg
>
>
>
> We’ve just tried TCP and the issue has gone away.
>
> Can anyone tell me why this happens? Also, what’s the reason for UDP being
> preferred over TCP?
>
> Thanks.
>
> -Stuart
>
> [SNIP]
>
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