Is IPsec IND-CCA secure provided the used block cipher is a pseudorandom function? I am trying to solve the question whether
"IPsec is IND-CCA secure provided the used block cipher is a pseudorandom function" (with IPsec using a variant of Encrypt-then-MAC)

As a resource I am given the paper
Mihir Bellare &amp; Chanathip Namprempre (2000). Authenticate
andd Encryption: Relations among notions and analysis of the generic composition paradigm

where I should focus on Theorem 3.2, which is the following implication:
INT-CTXT $\wedge$ IND-CPA $\rightarrow$ IND-CCA

Accordingly, I am trying to verify that the antecedent of the implication holds when using a pseudorandom function as a block cipher. I am currently stuck with the part whether the property of IND-CPA security holds. If I understood it correctly, the IND-CPA security depends on the mode of operation in which the pseudorandom function is used. 
In our lecture it was mentioned that an encryption scheme using a pseudorandom function as block cipher is indeed CPA-secure if the CTR mode (with a randomly chosen initial ctr) or the CBC mode is used. However, as far as I know it does not hold for other modes. 

Therefore, I would like to know which mode of operation is used by IPsec and whether my approach makes sense.
I would like to know which mode of operation is used by IPsec 


That depends on what is negotiated; if we assume we're using AES as the block cipher, then the standard modes (that is, ones which have transform numbers assigned by IANA) are CBC, CTR and GCM.


  and whether my approach makes sense.


Sounds good to me.