I have two subnets and am experiencing some pretty weird (to me) behaviour - could you help me understand what's going on?
Scenario 1
PC: 192.168.11.101/24
Server: 192.168.10.102/24, 192.168.11.102/24
From my PC I can connect to .11.102, but not to .10.102:
ping -c 10 192.168.11.102 # works fine
ping -c 10 192.168.10.102 # 100% packet loss
Scenario 2
Now, if I disable .11.102 on the server (ip link set <dev> down
) so that it only has an ip on the .10 subnet, the previously failing ping works fine.
PC: 192.168.11.101/24
Server: 192.168.10.102/24
From my PC:
ping -c 10 192.168.10.102 # now works fine
This is baffling to me... any idea why it might be?
Here's some additional information:
-
The two subnets are on different vlans (.10/24 is untagged and .11/24 is tagged 11).
-
The PC and Server are connected to the same managed switch, which however does nothing "strange" (it just leaves tags as they are on all ports).
-
The router is connected to the aformentioned switch and set to forward packets between the two subnets (I'm pretty sure how I've configured it so, plus IIUC the second scenario ping wouldn't work without forwarding).
-
The router also has the same vlan setup, and I can ping both .10.1 and .11.1 with no issue in both scenarios 1 and 2.
-
In case it may matter, machine 1 has the following routes, setup by networkmanager from dhcp:
default via 192.168.11.1 dev eth1 proto dhcp src 192.168.11.101 metric 410
192.168.11.0/24 dev eth1 proto kernel scope link src 192.168.11.101 metric 410
- In case it may matter, Machine 2 uses systemd-networkd and the routes generated from DHCP are slightly different (after dropping the .11.102 address for scenario 2, of course the relevant routes disappear):
default via 192.168.10.1 dev eth0 proto dhcp src 192.168.10.102 metric 100
192.168.10.0/24 dev eth0 proto kernel scope link src 192.168.10.102 metric 100
192.168.10.1 dev eth0 proto dhcp scope link src 192.168.10.102 metric 100
default via 192.168.11.1 dev eth1 proto dhcp src 192.168.11.102 metric 101
192.168.11.0/24 dev eth1 proto kernel scope link src 192.168.11.102 metric 101
192.168.11.1 dev eth1 proto dhcp scope link src 192.168.11.102 metric 101
I don't think I quite explained the situation well enough: my server only has 1 ethernet port (same as my PC), otherwise I wouldn't have bothered with vlans (well, I would still have bothered, since my house still only has one "backbone" cable running through it, but I would have configured it on the switches only).
Anyway... a few of the things you say/imply go against my understanding of networking, so one of us would better go back RTFM as you suggest :) (just kidding - most probably I just don't understand what you mean)