Since I upgraded my Synology 918+ NAS’s OS to DSM 6.2.3-25426 a few weeks ago my firewall logs have been filled with IP Spoofing errors which have originated at a port for the Plex server. I discussed this with Synology’s support and they identified the Plex server as the problem. When I shut down the Plex server the problem goes away.
My NAS is connected to my network over LAN1. LAN2 is not connected. The IP spoofing error has an IP address of the last assigned address for LAN2 although the signal is coming from LAN1. This is the reason my firewall identifies it as an IP spoofing error.
Prior to upgrading the NAS’s OS I did not have this problem and Plex works fine otherwise. ie When it is on I can connect from my various players and use it. This is more of an annoyance as my firewall is sending me logs every half hour since its logs are filling up with this error very frequently.
Is there anyway to fix this?
Thanks in advance.
Server Version#: 1.19.4.2902-69560ce1e
Player Version#:
What are the defined IP addresses for LAN1 and LAN2 ?
If both are on the same subnet, DSM itself causes the spoofing, contrary to what Synology tech support says. It’s because of how their internal router works. Such ‘spooling’ can easily be demonstrated by examining the MAC addresses when communicating with the two different adapters on the same LAN segment.
ChuckPa I’m only using LAN1. LAN2 is really only there for increasing bandwidth and I don’t have a switch which can map two ethernet cables to one IP address. So for now LAN2 is disconnected. The problem as you say is that the Firewall is seeing a different IP address for the same MAC address it already assigned an IP address for hence the IP Spoofing error. BigWheel’s solution worked for me.
Problem is back and the solution no longer works. I just upgraded my NAS OS to DSM 6.2.3-25426 Update 2. I also upgraded my Plex server to 1.19.5.3112-b23ab3896 at the same time. Preferred Network Interface is set to the correct LAN rather than Any but this has no effect anymore. I rebooted the NAS but the problem still occurs.
I am not using two Ethernet connections. I am only using one. The other Ethernet port is disconnected. And the Preferred Network Interface worked until I upgraded the NAS OS again. Now it no longer works.
The issue is that my Firewall log is filling up with IP spoofing errors as the Plex server appears to be broadcasting with the IP address of LAN2 which is not connected to anything on LAN1 so the Firewall identifies the MAC address of LAN1 but the incorrect IP address and identifies this as an IP spoofing error. I am not an IT expert so I have no clue how it is able to do this but I understand the problem for the firewall. Anyways the result is my e-mail box fills up with firewall logs which makes it a lot harder for me to spot legitimate problems. Otherwise as you say Plex seems to function fine. However I have to turn off the Plex server as this is a problem for my Firewall.
Well that is not really helpful to blame my firewall which is doing its job correctly. I do not wish to switch off IP spoofing checks as I work from home so this is also my office as well as home network and I need some level of security. How was it that Plex had no problems dealing with this for many years and is only now having difficulty with it since the last two upgrades of DSM? Perhaps the only solution is to get a switch which can bind the two ethernet connections or do the other thing you suggested but I still don’t see why Plex can’t handle a single ethernet connection. In the meantime Plex will stay off till I can find a workaround.
I did take up the issue with Synology and they told me it was a Plex issue which is why I came here. Don’t worry I’ve experienced this before in work where two software need to work together and don’t and both blame the other. This doesn’t help the end user.
Regardless thanks for your help. I will try to find a workaround at some point in the future by using both ethernet ports.
