TCP connection issues with SIMH VAX on Docker

[OrB]

I'm running a simulated VAXServer 3900 using SIMH, with an OpenVMS operating system.
Incoming communication works when running "natively" on a linux server, but doesn't work when running inside a Docker container.

I've managed to successfully configure networking in the OS using TCPWARE - when running "natively" on a linux server.
When running the same inside a Docker container, incoming communication (telnet, ftp) doesn't work (of course, I've re-configured TCPWARE).

To be more specific, I see packets coming in and identified as IP packets (when running netcu debug /ip), but it seems like they are not identified as TCP/UDP packets (when running netcu debug /tcp, nothing is shown).

Outgoing connections seem to work - I can connect to other servers using telnet.
When running netcu debug /ip, I see that the packets are identified with "pro=TCP".

I've tried to compare the packets (using Wireshark) for the working setup (natively on linux) and for the failing setup (in Docker), but they don't differ much.

I don't have TCPIP installed, I'm using TCPWARE V4.1-2 (Patch level V4.1-2A).

SIMH Version Info

MicroVAX 3900 simulator V4.0-0 Current        git commit id: 34a133ce
MicroVAX 3900 simulator V4.0-0 Current
    Simulator Framework Capabilities:
        64b data
        64b addresses
        Threaded Ethernet Packet transports:PCAP:TAP:NAT:UDP
        Idle/Throttling support is available
        Virtual Hard Disk (VHD) support
        RAW disk and CD/DVD ROM support
        Asynchronous I/O support (Lock free asynchronous event queue)
        Asynchronous Clock support
        FrontPanel API Version 12
    Host Platform:
        Compiler: GCC 4.8.5 20150623 (Red Hat 4.8.5-28)
        Simulator Compiled as C arch: x64 (Release Build) on Nov 11 2019 at 16:08:01
        Memory Access: Little Endian
        Memory Pointer Size: 64 bits
        Large File (>2GB) support
        SDL Video support: No Video Support
        PCRE RegEx (Version 8.32 2012-11-30) support for EXPECT commands
        OS clock resolution: 1ms
        Time taken by msleep(1): 1ms
        OS: Linux my-server 3.10.0-1062.9.1.el7.x86_64 #1 SMP Mon Dec 2 08:31:54 EST 2019 x86_64 x86_64 x86_64 GNU/Linux
        git commit id: 34a133ce
        git commit time: 2019-10-29T08:07:58-0700

SIMH configuration file (snippet)

set xq mac=<eth1 mac address>
attach xq0 eth1