Hello Friends @ 3000-L,
Re: Search priority of RESLVCNF, HOSTS and NMMGR/DNS and Caching
Wow, this is a HUGE topic... Let me see if I can pick out the truths and
dispose of the fallacies (my spell checker did not like falses and picked this
one instead) and then I will wrap it all up at the end...
--------------------------------------------------------------Tom Renz writes--
What is the search priority when using the RESLVCNF and HOSTS files and NMMGR
configurations? What I have read is that when DNS servers are defined in the
RESLVCNF file the HOSTS file is not accessed. What if I wanted to use a
combination of the RESLVCNF and HOSTS files, can we set up the system to look
first at the HOSTS file then the RESLVCNV file for domain names similar to a
UNIX environment. We want to rid the hard coded addresses assigned in NMMGR and
utilize the DNS servers as well as, if possible, use the HOSTS file to override
the DNS entries when testing is required. Thanks. tom Renz
--------------------------------------------------------------Tom Renz writes--
Q1: What is the search priority when using RESLVCNF and HOST files and NMMGR
configurations ?
A1: It depends on what services level software you are using ? NS-SERVICES
VT/DSCOPY/NFT/etc. or ARPA-SERVICES FTP/TELNET/ETC. ?
Q2: What I have read is that when DNS servers are defined in the RESLVCNF file
the HOSTS file is not accessed ?
A2: False, sort of. When a RESLFCNF file points to a valid DNS Server and the
DNS Server responds, the 3000 will *NOT* look at the HOSTS file. This is true
if the response from the DNS Server is positive or if the response is negative
(node name lookup reports unknown host), if any reply comes back from the DNS,
the 3000 will *NOT* look at the HOSTS file. The 3000 will look at the HOSTS in
only two cases 1. The DNS Server has crashed (or is unreachable) and does not
reply at all! or 2. The RESLVCNF.NET.SYS file does not exist.
Warning: Do not configure bogus (99.99.99.99) entries in the RESLVCNF.NET.SYS,
this will significantly degrade your name lookup search times. Are your users
complaining it takes a long time to get connected to a system ? Check to see if
your DNS is responding.
Q3: What if I wanted to use a combination of the RESLVCNF and HOSTS files, can
we set up the system to look first at the HOSTS file then the RESLVCNV file for
domain names similar to a UNIX environment.
A3: No. The 3000 does not support what is known in the UNIX environment as
NSSWITCH (fallback) capabilities. See Enhancement Request SR 5003443176. The
operation on the 3000 is similar to HP-UX version 9.x as described in the answer
#2 above.
Q4: We want to rid the hard coded addresses assigned in NMMGR and utilize the
DNS servers as well as, if possible, use the HOSTS file to override the DNS
entries when testing is required.
A4: Many sites have eliminated NMMGR NSDIR entries and rely on the DNS Server
pointed to on the 3000 by RESLVCNF.NET.SYS and only fall back to HOSTS.NET.SYS
when the DNS Server is down. We do not have a fall back mode for HOSTS.NET.SYS
as I have described in Answer #2 and #3 above.
--------------------------------------------------------Charlie Thomas writes--
I would also like to know if there is some mechanism, in the reslvcnf.net file
(or elsewhere) to trigger in order to have whatever name is found and resolved
on the DNS server put in cache memory on the HP3000 that made the request.
The machines I have running on DNS are not caching the addresses once they've
been looked up on the DNS server, and therefore it has to look at the sever
every time it needs to resolve the same address. What do I need to look for
here?
--------------------------------------------------------Charlie Thomas writes--
Q5: ...have whatever name is found and resolved on the DNS server put in cache
memory on the HP3000.
A5: No, this is not done on the 3000. As a mater of fact, the last time I
investigated caching of the result of a DNS lookup, a cache was also not
present/implemented on HP-UX. See Enhancement Request SR 4701259549.
--------------------------------------------------------Charlie Thomas writes--
The (default) search path is as follows > cache, probe, proxy, nsdir, reslvcnf
(DNS), hosts.net.... or falls off as "unresolvable". I had also thought
(and read?) that upon using a reslvcnf file, that hosts.net is not searched when
a search on the DNS server has failed to produce a result. In my tests, I
found that the system will look in the hosts.net file, as outlined above. I've
heard that on UNIX machines, you can define the path to search in a local hosts
file first, before searching DNS. Any corroboration of this?
Charlie Thomas
--------------------------------------------------------Charlie Thomas writes--
Q6: The (default) search path is as follows > cache, probe, proxy, nsdir,
reslvcnf (DNS), hosts.net.... or falls off as "unresolvable".
A6: Same as answer #1, No, It depends on what services level software you are
using ? NS-SERVICES VT/DSCOPY/NFT/etc. or ARPA-SERVICES FTP/TELNET/ETC. ?
Q7: I had also thought (and read?) that upon using a reslvcnf file, that
hosts.net is not searched when a search on the DNS server has failed to produce
a result.
A7: HOSTS.NET.SYS file will be used if the DNS Server is DOWN (or not network
accessible) and it produces NO reply. Any reply from a DNS server will result
in the HOSTS.NET.SYS file not being looked at. Same as answers #2 and #3 above.
Q8: I've heard that on UNIX machines, you can define the path to search in a
local hosts file first, before searching DNS. Any corroboration of this?
A8: I understand HP-UX has NSSWITCH (fallback) which gives them additional
flexibility in using the HOSTS file as a backup, but I am not totally aware of
the specifics and all the functionality, so I will leave this answer open for
input from others.
----------------------------------------------------------Kevin Newman writes--
I believe that you can change the priority in NMMGR with cache, probe, and
proxy. The others, I'm not sure about, but I do remember being able to change
those three.
Kevin Newman
----------------------------------------------------------Kevin Newman writes--
Q9: I believe that you can change the priority in NMMGR with cache, probe, and
proxy
A9: Yes, the priority can be changed as well as disabling cache, probe and
proxy.
Wrap it all up at the end
=========================
NS-SERVICES Name Lookup:
-----------------------
1. Cache - configured/enabled in NMMGR, learned as a result of a probe lookup
or loaded as a static name from NSDIR.
2. Probe - configured/enabled in NMMGR, probe packet is sent on the network and
the host which matches the request replies. The result is Cached.
3. Proxy - configured/enabled in NMMGR, probe proxy packet is sent on the
network and a host configured for probe proxy reply replies. The result is
Cached.
ARPA-SERVICES Name Lookup:
-------------------------
1. RESLVCNF - Configured in RESLVCNF.NET.SYS, which points (by IP address) to
a DNS Server. A DNS request is sent out to the DNS Server and it replies.
The result is not cached.
2. HOSTS - Configured in HOSTS.NET.SYS, which is only accessed if 1. a DNS
request is not replied to by a DNS Server or 2. a RESLVCNF files does not
exist. The result is not cached.
And now the million dollar question everyone is asking ? Q1: What is the search
priority when using RESLVCNF and HOST files and NMMGR configurations ? A1: It
depends on what services level software you are using ? NS-SERVICES
VT/DSCOPY/NFT/etc. or ARPA-SERVICES FTP/TELNET/etc. ?
NS-SERVICES VT/DSCOPY/NFT/etc. as you might guess use "NS-SERVICES Name Lookup"
first and then failing that then use "ARPA-SERVICES Name Lookup" (one note: If
you pass a 4 part or greater node name "james.atl.hp.com" at "NS-SERVICES Name
Lookup" it automatically bails out and jumps to the "ARPA-SERVICES Name
Lookup").
~and~
ARPA-SERVICES FTP/TELNET/etc. as you might guess use "ARPA-SERVICES Name Lookup"
first and then failing that then use "NS-SERVICES Name Lookup".
If you are every working with our friends at the HP-Response Center and you tell
them what is not working and they start asking you what is working or they are
testing with other services or tools, you now know they are trying to identify
if the "ARPA-SERVICES Name Lookup" works or if the "NS-SERVICES Name Lookup"
works or if :~( none of the above are working... Just another of the tools used
to isolate a failure in establishing a connection.
I hope this helps.
Regards,
James Hofmeister
Hewlett Packard
Worldwide Technology Network Expert Center
P.S. My Ideals are my own, not necessarily my employers.
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