There's many kinds of ramen. Pork is one of the most common. There's chicken ramen. There's salt ramen. There's soy sauce ramen. There's miso ramen. And there's every combination. Soy+Miso+Chicken, Chicken+Pork, Pork+Sardine+Miso, Salt+Shrimp+Pork, Tomato, Cheese :P
You will find it hard to know for sure if there's no pork though because even if it's labeled salt-ramen if you look at the details it might say made with pork as well.
You forgot the seafood based combinations! They have pure seafood bases too, though. My Japanese friend brought me to a shop in Tokyo that apparently specialised in a 100% seafood base/stock. It was light compared to the meat-based stock but equally good.
While it's not uncommon to mix in chicken, fish etc, virtually all ramen stock is pork based though. There are porkless variants, but you'd have to look pretty hard to find them.
You will find it hard to know for sure if there's no pork though because even if it's labeled salt-ramen if you look at the details it might say made with pork as well.