There are hundreds of different types of standardized bunkers, so called Regelbau. These are categorized by Heer (army), Luftwaffe (airforce) or Marine (navy), and by function.
In addition, there are a lot of Sonderkonstruktion (specialconstuction), which are made specially to, for instance, a coastalbattery. Some bunkers are also known as Vf's. Vf is abbreviation for Verstärkt feldmessig, which means field reinforced.
Later on, there will be some more information about the following bunker-types;
L401 - Emplacement for 8,8 cm Flak gun
L402 - Emplacement for 2 cm Flak gun
L403 - B II fire control post for heavy anti-aircraft battery
L404 - B I fire control post for heavy anti-aircraft battery
L405a - Radar bunker
L406a - Machinery bunker for generator and 150 cm searchlight
L407a - Ammunition bunker for heavy anti-aircraft battery
R501 - Group-shelter for a group of 10 men
R607 - Ammunition bunker II
R608 - Battalion & regimental headquarters
R622 - Twin group shelter for two groups of 10 men
R634 - 6-embrasured turret bunker
R667 - Small casemate for 5 cm KwK (Kampf Wagen Kanone)
R671 - Casemate for medium pivoting guns
R680 - Casemate for 7,5 cm Pak 40
Here is one of the two R671 at Varnes, with the original K332(f) canon.