First of all you need to make here a solid distinction in terms of LU functionality between:
1) SEP Client on the machine that is assigned to be a GUP
2) let's call it GUP functionality on the same machine
...both those elements (hovewer bundled they are) in terms of liveupdate and definitions download are completely separate. Both those elements will have the definitions as well stored in different locations on the drive. An example:
Client A request definition set from GUP B -> GUP B request this definition from SEPM, downloads it, stores locally and provides it as requested to Client A. Does it mean that after GUP downloaded this particular set of definitions the Client B is already updated with it? No. They stay separate, if Client B wants to update this definition it needs as well to request it from GUP B - even if this is the same machine.
Taking the above into consideration answers to your questions:
Q: Do GUPs get and read the GUP list? Do they use the GUP list to download their updates like the clients do?
A: SEP Client itself (point 1) reads the GUP list and can take the update from GUP on the same machine or it may even happen that it contacts GUP on another machine. GUP (point 2) cannot get any updates from other GUPs.
Q: So, if GUPs can talk to and get their updates (deltas) from other GUPs, then why wouldn't we turn all machines in to GUPs?
A: No, this is only the SEP client talking to other GUPs. GUP feature itself talks only! to SEPM for updates - no exception to that.
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On the general note - having 800 GUPs in 1000 clients environment seems to be an overkill - not sure if you spare here any network bandwith in that configuration. Have you considered Explicit GUP configuration - its a new feature introduced in SEP 12.1 RU2 that allows the sep clients to roam outside the scope of their own subnet for GUP communication. In the end effect you set up clients from different subnets to connect to particular GUP in other subnet. Have a look at some docus:
Understanding "Explicit Group Update Providers (GUPs) for Roaming Clients" in Symantec Endpoint Protection (SEP) 12.1.2
Article:TECH198640 |
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Created: 2012-10-19 |
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Updated: 2012-11-15 |
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Article URL http://www.symantec.com/docs/TECH198640 |
SEP 12.1 RU2 And Explicit Group Update Providers
https://www-secure.symantec.com/connect/articles/sep-121ru2-and-explicit-group-update-provider
How To Save Time Entering Multiple Explicit Group Update Providers (GUPs)
https://www-secure.symantec.com/connect/forums/how-save-time-entering-multiple-explicit-group-update-providers-gups