Name Resolution under TCP/IP-32

[Mark Hadfield]

As part of an effort to understand the conditions which cause longish
"pauses" with WfWg + TCP/IP-32, I devised the following experiment which
others may like to try:

METHOD and RESULTS:

1. Set the Windows clock going where you can see it.

2. Open a DOS box and type "ping abcdefghijklmnop". There is be a
delay of a few seconds (the length depending on whether a DNS Server is
specified in SYSTEM.INI) during which the clock continues to count out the
seconds. The command then returns "Bad IP address abcdefghijklmnop." In
other words, behaviour is normal. (I am assuming that abcdefghijklmnop is not
a valid host name on your system.)

3. Now type "ping abcdefghijklmno". This time the delay is longer. The clock
counts out a few seconds then freezes for the final 21 seconds. While the
clock is frozen, the system does not respond to keyboard or mouse input.

4. Add the following entries to the [DNS] section of SYSTEM.INI and save the
file. (It appears that you do not have to restart Windows for this change to
have effect.)

LocalPriority=1
HostsPriority=2
DnsPriority=3

5. Repeat step 3. The clock does not freeze.

6. Add a further line to the [DNS] section of SYSTEM.INI

NetbtPriority=4

7. Repeat step 3. The clock freezes.

EXPLANATION:

The LocalPriority, etc, entries are described in Microsoft Knowledge Base
article Q119372. (To search the knowledge base, point your WWW browser at
www.microsoft.com.) They determine the priority for the four different ways in
which TCP/IP applications resolve host names to IP addresses, ie: local cache,
hosts file, DNS server and NetBIOS-over-TCP/IP (NBT) broadcasts on the subnet.
The default, if none of these entries is found, is allegedly equivalent to:

LocalPriority=1, HostsPriority=2, DnsPriority=3, NetbtPriority=4

Omitting any entry (but including others) causes that method of name
resolution to be bypassed.

INTERPRETATION of RESULTS:

1: The 21-second "freezes" only occurred when NBT name resolution was enabled
(initially by default, later by an explicit NetbtPriority entry).

2: NBT name resolution only caused the system to freeze when the host name
was less than 16 characters. (Further experimentation confirms this.)

CONCLUSIONS:

There is a bug in resolution of names < 16 characters using NBT with the final
release of TCP/IP-32.

Unless you really need it (ie you want your Winsock apps to be able to contact
local machines by name without calling on a DNS server and without an entry in
your hosts file) turn off NBT name resolution by adding the following lines to
the [DNS] section of SYSTEM.INI

LocalPriority=1
HostsPriority=2
DnsPriority=3

This does not disable the use of NBT by Windows networking.

SPECULATION:

I wonder if all this is of any relevance to people who have reported system
crashes (apparently related to DNS) with the final release of TCP/IP-32.

APPENDIX;

In case anybody's interested, below are relevant SYSTEM.INI settings on
the PC on which the above tests were done. Final release of TCP/IP-32 was used
over ODI drivers:

[MSTCP]
EnableRouting=0
Interfaces=NE20000
deadgwdetect=1
pmtudiscovery=1
DefaultRcvWindow=3072

[DNS]
HostName=hadfield
DNSServers=131.203.1.5
DomainName=greta.cri.nz
DNSDomains=greta.cri.nz,grace.cri.nz,kelburn.cri.nz

[NE20000]
DefaultGateway=131.203.56.254
IPMask=255.255.0.0
IPAddress=131.203.56.182
Description=NE2000 Compatible
Binding=NE2000

[NBT]
LANABASE=0
LmHostFile=C:\WINDOWS\lmhosts
EnableProxy=0
EnableDNS=0

==============================================================
Mark Hadfield hadf...@storm.greta.cri.nz
NIWA (Taihoro Nukurangi) NIWA.GRETA:HADFIELD
Wellington, New Zealand