from grm one of the folks there has a bud who has been there
The Embassy is located in the nation's capitol city. It contains the Ambassador.
A Consulate is a section responsible for issusing tourist and immigration visas for entry to the United States, and assisting American citizens living and traveling in that country. It is headed by a Consul General.
Generally there will be a Consulate in each major city within the country, each with it's own Consul General. In the capitol city, the Consulate will be a section within the Embassy. All Consulates within the country are subordinate to the Embassy, and the Ambassador. There is only one Ambassador, but there is a Consul General for every Consulate.
MSGs are responsible for safeguarding Classified and Sensitive Information. Since Consulates normally do not contain any of this, being focused on issuing visas and other simple administrative work, they often do not have any Marines assigned to them. Some do, most do not.
Personal protection for the Ambassador is not a direct responsibility for MSGs. Ambassadors have their own bodyguards for whom that is the sole job. MSGs will protect the Ambassador, and any US Government personnel, if necessary and they are able, but their focus is preventing compromise of national security.
Hope that helped to clarify.
Update: Got some word from a Foreign Service friend of mine. Everything is still very confused and foggy, but he was able to give me a little better context.
1) The consulate in Libya was pretty ghetto. It was a converted one-floor motel building. The only reason the consulate was located there was because that was one of the only areas the rebels had under their control back when we first established relations with them. The diplomats got on the ground, looked around, and the motel was the first suitable building they could find to set up shop.
Bottom line though is that it was NOT very defensible. Apart from a few modifications, it was still largely a civilian structure. So use your imagination to infer what that implies.
Once the old regime was toppled, and the new embassy was established in the capitol of Tripoli, it was expected that either the motel-consulate would be closed altogether, or a new building would be acquired or built, but no action had been taken yet.
2) The attack on the Beghazi consulate was not a protest-gone-wrong. It likely had nothing to do with this supposed offensive movie either. It was a direct, planned, coordinated assault. It was a firefight that lasted for hours and hours. The attackers had heavy weapons, including heavy machineguns, RPGs, bombs, and possibly mortars. People don't bring that stuff incidentally to a normal protest.
While the details are still unclear, what likely happened was that there WAS a peaceful protest by some salifists going on outside in connection with the video, but a number of attackers used the protest as cover to launch their assault. Which implies some element of manipulation by the attackers, stirring up the protest in the first place (translating the movie into arabic?).
3) The normal Libyans are horrified. Chris Stevens was well liked, well respected, and the American presence relatively popular. Literally just a couple months ago, Ambassador Stevens announced that we would begin issuing US visas to Libyans again. The Libyans are genuinely grateful for the non-intrusive support for their revolution. When the attack commenced, the local Libyan security guards who were protecting the Consulate fought hard to defend it. Many (at least 20, possibly all of them) died at their posts, defending it (remember too how ghetto the defenses were). When Ambassador Steven's vehicle was hit by an RPG, attempting to evacuate from the scene, it was normal Libyans who pulled him out, and who took him and the other casualties to other American workers located nearby, and accompanied him to the hospital. It is possible that the angry civilian presence at the scene drove the attackers off, preventing them from following up on their attack.
4) Chris Stevens is a *moderated for GRM* hero. He was present as part of a planned visit to cut the ribbon for the grand opening of a new American Center building, so the fact that he would be there at that time was publically known. When the attack commenced, the personnel inside the Consulate went to their assigned places, but then the building was set on fire by the attackers. Ambassador Stevens apparently went into the burning building to rescue his people, and ensure the all got out to safety. It is likely that his death was contributed to by smoke inhalation as a result.
Take all of the above with a grain of salt. It's fourth-hand info.
But it does paint a very interesting picture.
p.s. Confirmed there are no MSGs in EITHER Benghazi, or Tripoli. Though now the diplomats in Tripoli are BEGGING for them to be sent some. Can't speak regarding FAST team elements.