Guest machine can't see the network

Issues related to configuring your network
Iucharbius
Posts: 8
Joined: 2022/11/02 14:33:48

Re: Guest machine can't see the network

Post by Iucharbius » 2022/11/20 17:59:10

That's the "pretty obvious" thing that I seem to have missed. I was planning on putting a nic on each subnet but hadn't gotten around to it. I wasn't aware that it would have a deleterious impact so I didn't clean this up earlier. I have disconnected the rest of the network connections and pointed the bridge to the one surviving NIC. It didn't fix the issue, but I do have a cleaner routing table now:

[iucharbius@kawadomek ~]$ ip r
default via 192.168.5.1 dev br0 proto dhcp src 192.168.5.31 metric 425
172.17.0.0/16 dev docker0 proto kernel scope link src 172.17.0.1
192.168.5.0/24 dev br0 proto kernel scope link src 192.168.5.31 metric 425
192.168.122.0/24 dev virbr0 proto kernel scope link src 192.168.122.1 linkdown


The bridge looks to be picking up the IP address as expected:

[iucharbius@kawadomek ~]$ ifconfig
br0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.5.31 netmask 255.255.255.0 broadcast 192.168.5.255
inet6 fe80::66fc:420c:b58a:2921 prefixlen 64 scopeid 0x20<link>
ether 14:02:ec:8a:64:21 txqueuelen 1000 (Ethernet)
RX packets 79432 bytes 47475135 (45.2 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 77343 bytes 267904155 (255.4 MiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

eno50: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether 14:02:ec:8a:64:21 txqueuelen 1000 (Ethernet)
RX packets 92289 bytes 49583251 (47.2 MiB)
RX errors 0 dropped 221 overruns 0 frame 0
TX packets 239811 bytes 276687606 (263.8 MiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0


The bridge has the right interfaces too:

[iucharbius@kawadomek ~]$ brctl show
bridge name bridge id STP enabled interfaces
br0 8000.1402ec8a6421 no eno50
vnet0
docker0 8000.024296befe72 no vethe9ac898
virbr0 8000.525400d0ca01 yes

It looks to be a lot less of a mess, but I'm still not getting an IP on the guest. I bet there's some other obvious thing that I'm missing.

I appreciate the help - I banged my head on this for days before posting. I didn't want to be "that guy" posting without doing any research. I also don't want to be the other "that guy" who fails to express gratitude for the help.

Cheers

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jlehtone
Posts: 4203
Joined: 2007/12/11 08:17:33
Location: Finland

Re: Guest machine can't see the network

Post by jlehtone » 2022/11/20 19:18:49

Do you have any (or plan to have) guests on the network "default" (192.168.122.0/24, that shows as "virbr0")?
If you don't then that too can be removed. It should not have any effect, but why have unnecessary things?

virsh net-list --all
should show all "networks" defined by libvirt. It should now have only one entry, the "default",
and if you have no need for it, then you can disable autostart for it.


How does the guest configure its network? With DHCP? If yes, then tcpdump on host should show activity on
the br0 when the guest boots and attempts to connect to the DHCP server.

Iucharbius
Posts: 8
Joined: 2022/11/02 14:33:48

Re: Guest machine can't see the network

Post by Iucharbius » 2022/11/23 00:10:27

I am down to the connections that I absolutely need - thanks for that tip. As suspected, it did not fix this issue, but will probably stave off future problems.

I tried a tcpdump on br0 but it was coming in too fast to parse out. I will have to figure out how to better filter it or perhaps dump it into a file that I can go through afterward. I was getting a page or two per second.

Thank you again for the help.

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TrevorH
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Location: Brighton, UK

Re: Guest machine can't see the network

Post by TrevorH » 2022/11/23 03:40:46

If you tcpdump the same connection that you use to ssh to the machine then you need to exclude port 22 from the tcpdump or it will loop dumping the packets that show the packets....
CentOS 8 died a premature death at the end of 2021 - migrate to Rocky/Alma/OEL/Springdale ASAP.
Info for USB installs on http://wiki.centos.org/HowTos/InstallFromUSBkey
CentOS 5 and 6 are dead, do not use them.
Use the FAQ Luke

Iucharbius
Posts: 8
Joined: 2022/11/02 14:33:48

Re: Guest machine can't see the network

Post by Iucharbius » 2022/12/04 21:54:23

I blocked port 3389 as I'm using XRDP. I saw a lot of traffic from my HomeAssistant server (ARP calls looking for the MAC address of the server I'm troubleshooting) and the answers back. What I'm not seeing is any activity over br0 from the guest machine when it boots up.

If I make a change to the network interfaces in the guest machine (it's TrueNAS Scale), I get an IP address (but no activity on my tcpdump) that is in the right subnet. I can even see the TrueNAS server on that IP address in my router. It seems like it should be working, and I can ping that IP from the host (but not anywhere else on the network).

Half a step forwards, it would seem.

EDIT: I can ping the host from the guest and ping the guest from the host, but I can't even ping the gateway -192.168.5.1 - from the guest (but I can from the host).

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