Docker compose and out-of-order TCP packets

Question

There are two Docker containers with the following configuration:

version: '2'

services:

  host:
    ports:
      - 8081:8081
    build:
      context: .
      dockerfile: Dockerfile
      args:
        PROJECT_DIR: Host
        PROJECT_NAME: Host
        WAIT_FOR_HOST: 0
    restart: on-failure

  client:
    depends_on:
      - host
    ports:
      - 8082:8082
    build:
      context: .
      dockerfile: Dockerfile
      args:
        PROJECT_DIR: Client
        PROJECT_NAME: Client
        WAIT_FOR_HOST: 1
    restart: on-failure

  tcpdump:
    image: kaazing/tcpdump
    network_mode: "host"
    volumes:
      - ./tcpdump:/tcpdump

Applications started on both of them communicate over TCP/IP.

Here is the network configuration:

[
    {
        "Name": "akkaremotetest_default",
        "Id": "4995d7e340e09e4babcca7dc02ddf4f68f70761746c1246d66eaf7ee40ccec89",
        "Created": "2018-07-21T07:55:39.3534215Z",
        "Scope": "local",
        "Driver": "bridge",
        "EnableIPv6": false,
        "IPAM": {
            "Driver": "default",
            "Options": null,
            "Config": [
                {
                    "Subnet": "172.19.0.0/16",
                    "Gateway": "172.19.0.1"
                }
            ]
        },
        "Internal": false,
        "Attachable": false,
        "Ingress": false,
        "ConfigFrom": {
            "Network": ""
        },
        "ConfigOnly": false,
        "Containers": {
            "6040c260c5195d2fe350bf3c89b5f9ede8a65d44da6adb48817fbef266a99e07": {
                "Name": "akkaremotetest_host_1",
                "EndpointID": "a6220a6fee071a29b83e30f9aeb9b9e7ec5008f04f593ff3fb2464477a7e54aa",
                "MacAddress": "02:42:ac:13:00:02",
                "IPv4Address": "172.19.0.2/16",
                "IPv6Address": ""
            },
            "a97078c28c7d221c2c9af948fe36b72590251be69e06d0e66eafd2c74f416037": {
                "Name": "akkaremotetest_client_1",
                "EndpointID": "39bcb8b1047ad666d9c568ee968602b3a93edb4ac2151ba9c3f3c02359ef84f2",
                "MacAddress": "02:42:ac:13:00:03",
                "IPv4Address": "172.19.0.3/16",
                "IPv6Address": ""
            }
        },
        "Options": {},
        "Labels": {}
    }
]

When I analyse network communication in Wireshark, I can see multiple out-of-order TCP packets.

Do you have any suggestions why that happens and how to fix it? This could be a possible solution to my other problem described here.

Answer 1

Can you look at the MAC addresses of the packets? If you look closely packet 77 and packet 78 have similar payloads. There is a possibility, the containers are sending out the packets with the MAC address of the bridge and the bridge is routing the packet.

ip route inside the containers can confirm if the communication between the packets is happening via routing or bridging.