Does Mikrtotek RB750GR3 router support DES? Any idea about which Mikrotek router with similar grade but support DES and MD5?
Why do you want to use obsolete algorithms? Both DES and MD5 are proven insecure, you should not be using them anywhere in your network.
I agree that using old algorithms is not advisable, please try using AES + SHA256.
If fore some reason you have to use them: RB750GR3 does support unaccelerated DES + MD5 and hardware accelerated 3DES+MD5.
Please look here: https://wiki.mikrotik.com/wiki/Manual:IP/IPsec#Hardware_acceleration