Ing. Ondřej Ševeček | GOPAS a.s. | MCM: Directory Services | MVP: Enterprise Security | | |

Active Directory Client Interactions

Central Database  LDAP – Lightweight Directory Access Protocol  database query language, similar to SQL  TCP/UDP 389, SSL TCP 636  Global Catalog (GC) – TCP/UDP 3268, SSL TCP 3269  D/COM Dynamic TCP – Replication  Kerberos  UDP/TCP 88  Windows NT 4.0 SAM  SMB/CIFS TCP 445 (or NetBIOS)  password resets, SAM queries  SMB/DCOM Dynamic TCP  NTLM pass-through  Kerberos PAC validation

Design Considerations  Distributed system  DCs disconnected for very long times  several months  Multimaster replication  with some FSMO roles

Design Considerations  Example: Caribean cruises, DC/IS/Exchange on board with tens of workstations and users, some staff hired during journey. No or bad satelite connectivity only. DCs synced after ship is berthed at main office.  Challenge: Must work independently for long time periods. Different independent cruise- liners/DCs can accomodate changes to user accounts, addresses, Exchange settings. Cannot afford lost of any one.

Database  Microsoft JET engine  JET Blue  common with Microsoft Exchange  used by DHCP, WINS, COM+, WMI, CA, CS, RDS Broker  %WINDIR%\NTDS\NTDS.DIT  ESENTUTL  Opened by LSASS.EXE

Installed services LSASS Security Accounts Manager TCP 445 SMB + Named Pipes Kerberos Key Distribution Center UDP, TCP 88 Kerberos Active Directory Domain Services UDP, TCP 389,... LDAP NTDS.DIT D/COM Dynamic TCP

Network Interactions (DC Location) Any DC Client LDAP UDP SRV: Any DC List Get My Site DNS SRV: My Side DC My Site DC 2000+

Network Interactions (2008/Vista+ DC Location) Any DC Client Vista+ LDAP UDP SRV: Any DC List Get My Site DNS SRV: My Site DC Next Closest Site Close Site DC My Site DC SRV: Close Site

Network Interactions (Join Domain) DC Client Kerberos SMB TGT: User SAM Interface TGT: CIFS

Network Interactions (Local Logon) DC Client Kerberos LDAP SMB TGT: User GPO List GPO Download TGS: LDAP, CIFS

Network Interactions (Kerberos Network Logon) DC Client Kerberos Server App Traffic DC SMB D/COM TGT: User In-band TGS: Server Occasional PAC Validation TGS: Server D/COM Dynamic TCP

Network Interactions (NTLM Network Logon) DC Client Server App Traffic DC SMB D/COM In-band NTLM Pass-through NTLM D/COM Dynamic TCP

Network Interactions (Basic/RDP Logon) DC Client Server App Traffic DC In-band clear text Kerberos TGT: User

Active Directory Replication

Attribute Types  string, integer, datetime, boolean, binary  DN reference  multivalue  up to 5000 items  linked multivalue  unlimited, requires 2003 Forest Level  backlink  memberOf  computed  primaryGroupToken, tokenGroups, lastLogonTimestamp  write/only attributes  unicodePwd

Group membership Sales CN=Kamil,OU=London,DC=... CN=Judith,OU=Paris,DC=... CN=Victor,OU=London,DC=... CN=Stan,OU=London,DC=... member Judith CN=Sales,OU=Groups,DC=... CN=IS Access,OU=Groups,DC=... memberOf Link Backlink

(Not)replicated attributes  Not replicated  logonCount  badPasswordCount  badPasswordTime  lastLogon  lastLogoff  Replicated  pwdLastSet  lockoutTime  lastLogonTimestamp (since 2003)

Logon timestamps (2003 DFL) Client DC lastLogon11:38 lastLogon9:00 lastLogon- lastLogonTimestamp11:00 lastLogonTimestamp11:00 lastLogonTimestamp11:00

lastLogonTimestamp  Requires 2003 domain level  Updated only once per 14-random(5) days  DC=idtt,DC=local  msDS-LogonTimeSyncInterval  1+ – minimum without randomization  5+ – randomization starts  14 – the default ...

Password changes Password Change Immediate Replication password hash Normal replication DC PDC Client

Password changes Client DC PDC pwdLastSet

Authentication failures DC PDC pwd1 DC pwd1 Client

Authentication failures DC PDC pwd1 DC pwd2 Client pwd2

Authentication failures Client PDC pwd2 DC pwd2 DC pwd1

Authentication failures ClientDC badPasswordCount3 2 PDC badPasswordCount7 lockoutTime DC badPasswordCount2

Active Directory Client Interactions

Client Applications  Kerberos and NTLM authentication  Secure Channel  password changes, NTLM pass-through, Kerberos PAC validation  Group Policy client  DFS client  Certificate Autoenrollment client

Client Applications  NPS (IAS), RRAS, TMG (ISA), RD Gateway (TS Gateway)  group membership, Dial-In tab  RD Host (Terminal Server)  Remote Control tab etc., Licensing servers  DHCP Server  authorization  IIS  account and group membership for SSL certificate authentication  WDS  computer MAC addresses or GUIDs

Connection Properties  Bandwidth (Mbps)  forget about this  Latency (ms)  round-trip-time (RTT)  SMB, D/COM, SQL  Packet Loss (per sec., per Mb)  packet loss rate (PLR)  VPN such as PPTP, SSTP, IP-HTTPS

Timeouts  DNS  primary DNS = 1 sec.  secondary DNSs = 2 sec.   ARP  ms 1000 ms  LDAP UDP Site Location  600 ms  TCP  SYN = 21 sec. (3x retransmission)  PSH/ACK = 93 sec. (5x retransmission) 

Basic DC location  Know the DNS name of the domain  Query general DNS DC SRV records  _ldap._tcp.dc._msdcs.idtt.local  Ping DC  Windows  LDAP UDP (ping) DC  to get the client’s site/close site

DNS Domain Location  Makes use of DNS round robin  Site unaware lookup  NSLOOKUP  SET Q=SRV  _ldap._tcp.dc._msdcs.idtt.local  Site specific lookup  NSLOOKUP  SET Q=SRV  _ldap._tcp.Paris._sites.dc._msdcs.idtt.local

London x.x Site Example – Single Site DC1DC2DC3 Client DC4 DC5

Paris x.x London x.x Site Example – Multihomed DC (DNS Bitmask Ordering) DC1DC2DC3 Client DC4 DC5

Berlin x.x Paris x.x Roma x.x London x.x Site Awareness DC1DC2DC3 DC4 DC5 DC6 Client where I am?AnonymousLDAPUDP

General Operation  Use DNS to find generic DC list  Ping selected DC  Windows  Anonymous LDAP (UDP) to determine site  DC defines site from the request source IP address (NAT?)  Use DNS to find close DC in site  Ping or LDAP UDP to determine availability

DC Locator  NetLogon Service  nltest /sc_query:idtt  no network access  nltest /sc_verify:idtt  tries to authenticate with the DC  nltest /sc_reset:idtt  always performs new DNS lookup  nltest /dsgetsite  anonymous query against selected DC

DFS Client (MUP)  Multiple UNC provider (MUP) driver  Determines its own DFS server referrals  obtains the list of DFS root servers from AD using the default DC from Netlogon  SYSVOL may be accessed from a different DC  DFSUTIL /PKTINFO  Windows Server 2003/Windows XP  DFSUTIL CACHE REFERRAL  Windows Server 2008/Windows Vista

Paris x.x Cyprus x.x Roma x.x London x.x Site Example – Empty Site DC1DC2DC3 DC4DC5 DC6 DC7 Berlin x.x Client DC4DC5

Automatic Site Coverage  Each DC registers itself for its neighboring empty sites  HKLM\System\CurrentControlSet\Services\N etlogon  AutoSiteCoverage = DWORD = 1/0  GPO: Sites Covered by the DC Locator DNS SRV Records

Active Directory Troubleshooting

Paris x.x Cyprus x.x Roma x.x London x.x Site Example – Out of Site DC1DC2DC3 DC4DC5 DC6 DC7 Berlin x.x Client

Out-of-site clients

Limiting generic DC list  Limit creation of generic DC DNS records  GPO: Computer Configuration – Administrative Templates – System – Netlogon – DC Locator DNS Records  DC Locator DNS Records not Registered  Ldap, Kdc

DC Stickiness  When one close selected, client sticks to it  even when moved into a different site  must reset secure channel  Force rediscovery interval GPO  Vista+  hotfix for Windows XP  also registry value ForceRediscoveryInterval

Paris x.x Cyprus x.x Roma x.x London x.x Site Example – Moving Client DC1DC2DC3 DC4DC5 DC6 DC7 Berlin x.x Client DC4DC5 previously in Paris

Active Directory Troubleshooting

Berlin x.x Paris x.x Cyprus x.x Roma x.x London x.x Site Example – Failed DC DC1DC2DC3 DC4 DC5 DC6 DC7 Client

Non-close Site DC  Close site  client’s site  next closest site if enabled  If there is not DC available in the close site, rediscovery every 15 minutes  HKLM\System\CurrentControlSet\Services\Netlog on\Parameters  CloseSiteTimeout = REG_DWORD = x seconds

Paris x.x Cyprus x.x Roma x.x London x.x Site Example – Close Site DC1DC2DC3 DC4DC5 DC6 DC7 Berlin x.x Client

Try Next Closest Site  First get any DC name from DNS  Second query the DC for clients site name  returns the clients site  plus the closest site (determined by the DC)  Then query DNS for DCs in its current site and then tries to use the DCs  If none responds, the client queries DNS for its next closest site and tries to use the found DCs

Try Next Closest Site  Does not consider RODC sites by default  Can be change in registry  NextClosestSiteFilter  Windows cannot return the next closest site information  problem if the hit “any DC” is Windows  it is then going to be used regardless of its site

Client Rules Recap  Windows  In current site  In any site  Windows Vista+ with Next closest site  In current site  In the closest site  In any site  If the client is out of any site, find any dc  consider creating subnets for VPNs etc.

Active Directory Client Interactions

Site Link Design

Site Link Design (Better?) London Olomouc Roma Cyprus Paris Berlin

Site Link Design (Worse?) Olomouc Roma Cyprus Paris Berlin London

Active Directory Client Interactions

DNS Integration  Clients find DCs by domain/site name  DCs find replication partners according to their GUID  Netlogon de/registers locator records  DNS stores its data in  domain partition  DomainDnsZones application partition  ForestDnsZones application partition

Netlogon de/registration  Netlogon registers its own records at startup and deregisters them at shutdown  requires DNS registration enabled on at least one network adapter  %windir%\System32\Config\netlogon.dns  It does not touch others’ records  Autosite coverage  turned on by default

AD Integrated Zones  Offer Secure Dynamic Update  Timestamping  trimmed to whole hour  Aging and scavenging  records deleted by default between days of their age

DNS Application Partitions  Domain partition  CN=MicrosoftDNS,CN=System,DC=...  DomainDnsZones  replicated to all DNS Server which are also DCs for the domain  ForestDnsZones  replicated to all DNS Server which are also DCs for the forest

Secure Dynamic Update  Client side feature  DHCP Client on Windows  DNS Client on Windows Vista+  DNS Server must be on DC to authenticate clients with Kerberos  All Authenticated Users  can create new records  When a record is created, only the creator/owner can modify/update it

Secure Dynamic Update  Updates done regularly by clients  every hour by default  Default TTL is 20 minutes  Disable DHCP dynamic updates  insecure!

Dynamic Update Primary DNS Secondary DNS Client DNS SOA Update

Adjust A/PTR Record TTL

Dynamic Update and Replication DNS AD DNS 0 sec sec. 0-3 min. schedule

Dynamic Update and Replication

Dynamic DNS Update on RODC  Each writable DC returns itself as a primary DNS  RODC returns either (random) writable DC as the primary DNS

Dynamic DNS Update on RODC DNS ADRODC R/O DNS 0 sec. Client SOA Upd 1 2

Dynamic DNS Update on RODC DNS ADRODC R/O DNS 0 sec. 0-3 min. Client replicateSingleObject 0 sec.

Time stamping/Aging  Record Created  timestamp trimmed to whole hour  No-refresh period starts  by default 7 days  timestamp does not change if the record does not change  Refresh period follows  by default next 7 days  timestamp gets updated at the first update

Scavenging  Server wide configuration  Should be done by only one DNS Server as best practice  By default ocurres only once per 7 days

DNS Aging and Scavenging  per-zone setting  implemented by all DNS servers  timestamp updates only during the refresh interval  limits replication traffic

DNS Aging and Scavenging  per-server setting  should be done only by one of the DNS servers

DNS Aging and Scavenging

DNS Best Practice DC1 DNS DC2 DNS AD

DNS Waiting for AD

DNS Best-Practice Reasons  Faster boot time without errors and timeouts  Deregistration at shutdown is recorded in live DNS Server  would have problems replicate if sent into shutting-down DC

Client DNS balancing  Clients do not balance DNS servers  queries/updates  use the first one always if possible  DHCP server does not use round robin  Configuration must be done “manually”  manual on servers  more DHCP scopes for clients

Client DNS non-balancing  Always alternate DNS server IP addresses

Client DNS non-balancing DNS1 DNS2 Client1 DNS1 DNS2 Client2 DNS1 DNS2 Client3 DNS1 DNS2

DNS Client Settings  HKLM\System\CurrentControlSet\Services\Tc pip\Parameters  Timetouts  DNSQueryTimeouts  Disjoint namespace on multihomed machines  DisjointNameSpace  PrioritizeRecordData  GPO – DNS Suffix appending on Vista+

DNS Server UDP Pool  After applying KB , DNS Server reserves 2500 UDP ports  HKLM\System\CurrentControlSet\Services\D NS\Parameters  SocketPoolSize = DWORD = 2500  DNSCMD /Config /SocketPoolSize 2500

DNS Cache Pollution  server: idtt.com authoritative DNS server  question: test.idtt.com, type A  answer: no records  authority answer:  idtt.com SOA  idtt.com NS ns37.domaincontrol.com  ns37.domaincontrol.com A

Active Directory Troubleshooting

General Best Practice  Create and assign subnets for any possible client IP  Limit the general (site unaware) DNS registration of DCs  Enable Try next closest site and Force rediscovery options  Enable DNS Aging and Scavenging  Alter clients’ DNS settings to rotate the DNS server addresses

Ondřej Ševeček | GOPAS a.s. | MCM: Directory Services | MVP: Enterprise Security | | |