You need to use a Netherrack block, as all other blocks burn up or won't catch on fire.
Nethererrack burns for ever.
gaming.stackexchange.com/users/7283/Ray Britton
Prior to the 1.3 patch, you could make an infinite fire by lighting a block of wood / log on fire so that only one side is burning, and it would stay infinitely burning.
However, that was fixed in 1.3, so now the only way of having a block infinitely lit on fire is to get Netherrack somehow (be it buying it from an in-game shop, mining Coal Ore with a Golden Pickaxe if your server has the Golden Nether mod, or simply going to the Nether if your server supports it) and lighting it.
gaming.stackexchange.com/users/18/Kevin Yap
There used to be a bug that allowed you to do infinite fire, however, it was removed.
Now the only way is to harvest Netherrack from the nether.
Then you can use flint and steel to light it once you have placed the netherrack down.
In SMP you would need a nether world or use the /give command.
gaming.stackexchange.com/users/8388/Ja5087
You could use a netherrack block.
Just mine it from the nether.
Alternatively, you could use /give
[user] 87 to get yourself a netherrack block.
This would be the only solution other than using a plugin.
Netherrack fires never burn out and if you want to read about them, check the Minecraft Wiki, Netherrack article.
gaming.stackexchange.com/users/38416/MerajA
/gamerule
doFireTick false will make all fires burn infinitely without spreading.
gaming.stackexchange.com/users/61294/user61294
You can harvest netherrack and use that, but unless you want a fireplace why get a never ending fire?
Also, light the netherrack with a fire charge/flint and steel.
gaming.stackexchange.com/users/42803/Tcr
You need Netherrack, a block that makes fires burn unlimitedly.
Netherrack Netherrack can be found in the Nether, a dimensions that can be accessed by a portal built by 4 by 5 obsidian blocks.
But keep the inner blocks empty.
Then light the obsidian with flint and steel and the portal should be active.
The Nether is full of Netherrack, so it's easy to collect.
Once Netherrack is lit, the fire burns forever.
gaming.stackexchange.com/users/127996/Jim Jones
yes infinite time fire is possible.
things you need: flint and steel (alternatively firecharge)
netherrack that is found in nether.
netherrack looks like this (the block below the fire) the nether rack is found in nether which looks like a hellish place.
look the screenshot below
gaming.stackexchange.com/users/90465/Fennekin
I was wondering, how can I make a never ending fire in Minecraft? (I want to use it in SMP)
How can I make an infinite fire?
gaming.stackexchange.com
<minecraft-java-edition>
gaming.stackexchange.com/questions/17693
gaming.stackexchange.com/users/7546/shawn5657
You need to use a netherrack block as it burns forever.  Infinite fire can be made by lighting a Netherrack block.
The community suggests that infinite fire can be made by using a certain type of material.