HP StorageWorks Storage Mirroring application notes Guidelines for networking and failover (T2558-96063, February 2008)

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NOTE: The sample scripts provided are only examples. Because no two environments or configurations
are exactly the same, you
MUST modify the sample scripts in order to make the solution work in your
environment.
SAMPLE_FAILOVER.BAT
The following sample failback script will return the SPNs back to the original configuration.
SAMPLE_FAILBACK.BAT
If the target server is a domain controller, any SPNs added to its computer account will be removed
periodically. This is a normal domain controller function and will not affect client access. However, since
there are no SPNs for the source name, it may be possible for clients to be inadvertently or maliciously
redirected and connected to another server while in a failover state.
Name caching
By default, Windows systems cache DNS and NetBIOS name resolutions in the DNS Resolver Cache and
NetBIOS Remote Cache Name Table respectively. This functionality does not impede the ability of clients to
access the source name after failover as long as the appropriate WINS and DNS changes are made. Even
in name-only failover scenarios (where the IP address is not failed over), clients will use WINS or DNS to
re-resolve the name if an attempt to initialize a session with the cached entry fails.
Although name caching does not present any issues if WINS and DNS are updated after failover,
information about the entries in the name cache may be useful in troubleshooting if difficulties are
experienced. The cached entries can quickly show whether the client has resolved the source name to the
correct IP address.
A system's NetBIOS Remote Cache Name Table can be viewed by using the
nbtstat -c command, and
the
ipconfig /displaydns command displays the DNS Resolver Cache. The NetBIOS and DNS name
caches can be purged with the
nbtstat -R (the -R is case-sensitive) and ipconfig /flushdns
commands respectively.
Microsoft Knowledge Base articles 120642, 245437, and 187709 contain information regarding the
configuration of timeout values for the NetBIOS and DNS name caches. However, keep in mind that the
name resolution cache settings do not need to be adjusted for successful failover. If WINS and DNS entries
are updated properly, previously-cached name resolutions will not impede the ability of clients to establish
SMB sessions with the target server.
Storage Mirroring failover and ARP
After TCP/IP has resolved the host name to an IP address, it passes the IP packet to ARP (Address
Resolution Protocol). ARP resolves the IP address to an adapter MAC (media access control) address and
then passes the packet to the data-link layer (Ethernet, Token Ring, ATM, etc.). ARP maintains a cache of IP
address-to-MAC address resolutions on each system. This cache must be updated at failover so that clients
with cached entries will not attempt to send packets to the source's MAC address.
NSISPN -D HOST/SOURCE.domain.com SOURCE
NSISPN -D HOST/SOURCE SOURCE
NSISPN -D SMTPSVC/SOURCE.domain.com SOURCE
NSISPN -D SMTPSVC/SOURCE SOURCE
NSISPN -A HOST/SOURCE.domain.com TARGET
NSISPN -A HOST/SOURCE TARGET
NSISPN -A SMTPSVC/SOURCE.domain.com TARGET
NSISPN -A SMTPSVC/SOURCE TARGET
NSISPN -D HOST/SOURCE.domain.com TARGET
NSISPN -D HOST/SOURCE TARGET
NSISPN -D SMTPSVC/SOURCE.domain.com TARGET
NSISPN -D SMTPSVC/SOURCE TARGET
NSISPN -A HOST/SOURCE.domain.com SOURCE
NSISPN -A HOST/SOURCE SOURCE
NSISPN -A SMTPSVC/SOURCE.domain.com SOURCE
NSISPN -A SMTPSVC/SOURCE SOURCE