How do mods work in multiplayer?

So I plan on getting the mod that gives me slots specifically for my armor and some quick time slots, and also a mod that allows me more things to plant. The former just seems like a good mod, I understand the way the game works is how these games usually are when it comes to equipment but I just like having the armor slots, and the latter I won't use outside of planting a single oak tree in the middle of my future build as I'd prefer that over using the console and will probably remove the mod immediately after planting it.

My question is, how is this going to work if I have these mods installed while my friend doesn't? I assume the planting one will be fine, but what about the other one? Is it still going to work when he doesn't have the mods, or is this going to create some problems?
2:13 pm, June 22, 2021
Beautiful Ham Sandwich 0 comments 0 likes

aelthing replied to How do mods work in multiplayer? June 22, 2021 @ 3:28:49 pm PDT

yes it will create problems all players have to be set up the same, same mods and same date with updates. you cant game with modded and unmodded players ive tried
2:13 am, June 23, 2021
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Ryzilynt replied to How do mods work in multiplayer? June 22, 2021 @ 3:59:23 pm PDT

You can certainly game with modded and unmodded players. Ive done it, maybe not with all mods.

Some mods are server side , most are player side.

*edit : my experience is on a privately owned dedicated server.
2:13 am, June 23, 2021
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Arcayon replied to How do mods work in multiplayer? June 22, 2021 @ 4:29:31 pm PDT

Originally posted by aelthing:
yes it will create problems all players have to be set up the same, same mods and same date with updates. you cant game with modded and unmodded players ive tried

This isn't true. As a server owner I can tell you 100% this is false.


Originally posted by Beautiful Ham Sandwich:
My question is, how is this going to work if I have these mods installed while my friend doesn't? I assume the planting one will be fine, but what about the other one? Is it still going to work when he doesn't have the mods, or is this going to create some problems?

The way servers work in Valheim is the server hands off calculations to a localized host. So lets say you have skyheim installed and your friend doesn't. As a localized host, your client does all the calculations for everyone around you in a specific zone on the server. Lets say you shoot a fireball at the person without mods. He will still take damage as the damage calculation was done on your client. He won't see the effect though as he has no files to reference the effect.

If the localized host doesn't have the mods installed, there is risk of a crash when another person uses a mod around them. This is as the client can't understand what the person with a mod is trying to do.

This hand off process is inherently really bad for security, network optimization, and mod enforcement. Some mods like Valheim Plus will enforce their mod on the users who connect, but other mods do not. Your best bet is to ensure client and server side mods match for all players.
2:13 am, June 23, 2021
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Beautiful Ham Sandwich replied to How do mods work in multiplayer? June 22, 2021 @ 5:18:12 pm PDT

Originally posted by Arcayon:
Originally posted by aelthing:
yes it will create problems all players have to be set up the same, same mods and same date with updates. you cant game with modded and unmodded players ive tried

This isn't true. As a server owner I can tell you 100% this is false.


Originally posted by Beautiful Ham Sandwich:
My question is, how is this going to work if I have these mods installed while my friend doesn't? I assume the planting one will be fine, but what about the other one? Is it still going to work when he doesn't have the mods, or is this going to create some problems?

The way servers work in Valheim is the server hands off calculations to a localized host. So lets say you have skyheim installed and your friend doesn't. As a localized host, your client does all the calculations for everyone around you in a specific zone on the server. Lets say you shoot a fireball at the person without mods. He will still take damage as the damage calculation was done on your client. He won't see the effect though as he has no files to reference the effect.

If the localized host doesn't have the mods installed, there is risk of a crash when another person uses a mod around them. This is as the client can't understand what the person with a mod is trying to do.

This hand off process is inherently really bad for security, network optimization, and mod enforcement. Some mods like Valheim Plus will enforce their mod on the users who connect, but other mods do not. Your best bet is to ensure client and server side mods match for all players.
Thanks, this is actually very helpful, seeing the first two answers completely contradict each other confused me a bit.

Thankfully, the only mod I now plan on using is Plant Everything for the single oak tree I mentioned, and it seems like even if the other person doesn't have it it's not like they can't already see oaks. I'll still see if they can install it themselves just in case I'm totally wrong about this not creating an issue.
2:13 am, June 23, 2021
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