The Id for the nether portal block is 90 so doing /i 90 will give you this block. I have seen on some servers where there are "pools: of nether portal blocks placed by players in creative modes so i set out to do the same in my builds. However placing one next to another will delete both blocks. how are people able to place more than one nether portal block in the same area if it just deletes them?
Well I think you are wrong I was able to do a massive portal in a multiplayer world with my girlfriend. No mods were used and I know this because it was my server. I don't know why I can't place the portal blocks next to each other anymore.