LAN reconfig on Ubuntu Server post install

[Ethan Evans]

Someone asked for the complete results of ifcong, so here they are:
  Lo: flags=73<UP, LOOPBACK, RUNNING> mtu 65536
    inet 127.0.0.0  netmask 255.0.0.0
    inet6 ::1  prefixlen 128  scopeid 0x10<host>
    loop txqueuelen 1000 (Local Loopback)
    RX packets 905  bytes 249324
    RX errors 0 dropped 0 overruns 0 frame 0
    TX packets 905 bytes  249324
    TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

Additionally, someone asked if the name of the NIC changed. Short answer is
I don't know. The NIC before and after the motherboard swap was/is whatever
is built-into the motherboard. So if the 'name' of the NIC is something
like how drives may be given an dev/sda# assignment, then it still may or
may not have changed. If the name of the NIC is more like how drives have a
UUID, then it very likely changed. I've also included the results of "lshw
-class network" here, bellow:
  *- network DISABLED
    descriptoin: Ethernet interface
    product: RTL8111/8168/8411 PCI Express Gigabith Ethernet Controller
    vendor: Realtek Semiconductor Co, Ltd.
    physical id: 0
    bus info: pci at 0000:01:00.0
    logical name: enp1so
    version: 06
    serial: 70:85:c2:8c:4b:52
    size: 100Mbit/s
    capacity: 1Gbit/s
    width: 64 bits
    clock 33MHz
    capabilities: pm msi pciexpress msix vpd bus_master cap_list ethernet
physical tp mii 10bt 10bt-fd 1-bt 100bt-fd 1000bt 1000-bt-fd autonegotiation
    configuration: autonegotiation=on broadcast=yes drivers=r8169
driverversion=2.3LK-NAPI duplex=full latency=0 link=no multicast=yes
prot=MII speed=100Mbit/s
    resources: irq:22 ioport:e000(size=256) memmory:9d104000=9d104fff
memory:9d100000=9df103fff

On Sun, Dec 16, 2018 at 11:54 PM Ethan Evans <eevansnm2.0 at gmail.com> wrote:

> So in August I set up a basic Ubuntu server on a spare-parts PC because I
> wanted to run a Plex Media Server as a little project. However, being my
> spare-parts PC, it had a Haswell i5 in it that I thought was more than
> necessary for its task. I had also promised my brother my spare parts for
> an entry-level gaming rig once he settled into his own apartment. My older
> brother has just settled into an apartment (after being away for a few
> months to do training for work) and in preparation to hand over my
> spare-parts PC, I replaced the motherboard in the Plex server with an
> ASRock J3355M embedded-CPU motherboard. The CPU is not powerful, but is
> very power-efficient and I only use Plex for music streaming, so I believed
> it would be powerful enough for what I use it for. But now the system will
> not/cannot connect to the internet.
>
> When I first installed and setup the server, I gave it a static IP address
> on the LAN and setup port-forwarding to it. But our home network has a
> dynamic IP address, so as long as I logged into the plex.tv website, I
> could get the IP address of the home network and SSH into the server. After
> installing the new motherboard, I booted the server and discovered the Plex
> app on my phone could not find the server. I then began trying to
> trouble-shoot on the server itself. I first tried to ping 1.1.1.1 and
> 8.8.8.8 (DNS servers) and those failed completely with the message:
> "connect: Network is unreachable." I then tried to ping 192.168.0.1 (the
> LAN router IP address) and it failed with the same results. Using the
> command ifconfig, I get the following (partial results): "inet 127.0.0.1
> netmask: 255.0.0.0" I think expected results would've been something like:
> "inet 192.168.0.xxx netmask: 255.255.255.0" My guess is that the new LAN
> chipset or whatever on the new MoBo has reset the LAN settings for the
> server, but now I don't know how to set them again or if I might need to
> try and install different drivers for it to work. Short of reinstalling the
> entire Server OS, I don't know what to do. I could do that, but I'm hoping
> it's unnecessary and am asking for your help.
>
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