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The difference between host in connection properties and uname -a.

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Tnmkon
Occasional Collector

The difference between host in connection properties and uname -a.

Hello!

I have a rather silly question.

There is host "aaa" in properties of my connection but the command "uname -a" gives me other nodename "bbb". And when I'm trying to connect to "bbb" the connection is failed. What's the difference between host and node then?

 

 

P.S. This thread has been moved from HP-UX > General to HP-UX > networking - HP Forums Moderator

6 REPLIES
Matti_Kurkela
Honored Contributor
Solution

Re: The difference between host in connection properties and uname -a.

"bbb" is the name specified in /etc/rc.config.d/netconf on the HP-UX system as the hostname/nodename. If the hostname is 8 characters or less, the hostname and nodename are the same. But if the hostname is longer than that, HP-UX requires that a separate nodename of 8 characters or less is chosen, to allow compatibility with legacy applications using an old API that restricted the host/nodename to 8 characters or less.

 

The hostname usually should be associated with the primary IP address of the HP-UX system, but it may or may not be.

 

HP-UX generally does not "announce" its name automatically: there is no DDNS update support in standard HP-UX. It is the sysadmin's job to make sure the DNS has correct hostname/IP information for the HP-UX host, if so desired.

 

Changing the host/nodename of the HP-UX system is usually easy, but if there is some third-party software whose license is tied to the hostname, that might be a reason to keep an old hostname configured even if the host is known by another name in the network.

 

When your workstation looks up the IP address corresponding to the name "aaa", it apparently gets an IP address that will allow it to connect to the HP-UX host that identifies itself as "bbb".  The name -> IP mapping may be stored in the hosts file of your workstation, or in the DNS. Someone might have forgotten to update this information at some earlier point.

 

If the network at your site is a result of company mergers or similar, there might be overlapping hostnames and/or IP addresses. As a result, there might be DNS aliases, VPN tunnels or NAT mappings to allow connection past whatever overlaps there might be. (Hopefully these are only temporary solutions, and someone is already planning the overhaul required to fix the overlaps.)

 

You might want to run "nslookup aaa" and "nslookup bbb" on your workstation and see the IP addresses associated with each name. If the name "aaa" is associated with the correct IP address of the HP-UX host, and the name "bbb" is associated with a wrong IP address or no IP address at all, you might want to contact the DNS administrator of your site and describe the problem to him/her.

 

If the address from "nslookup aaa" is different from any IP address the HP-UX server has, then there might be a VPN tunnel or a NAT mapping involved - contact a network administrator of your site to get the details in that case.

 

The DNS administrator can certainly add the new name "bbb" to the DNS with the correct IP address (or even with the VPN/NAT address if it is more useful than the real address) - but before having the old name "aaa" removed from DNS, make sure that any production applications are not using that name to contact the server!

MK
Tnmkon
Occasional Collector

Re: The difference between host in connection properties and uname -a.

I see...

So if the "aaa" IP address is the same as the "bbb" and no one forgot nothing does that mean that probably DNS aliases there are?

Sorry for these maybe a bit stupid questions but I really want to understand )

Matti_Kurkela
Honored Contributor

Re: The difference between host in connection properties and uname -a.

If the IP address is the same for both names, then yes, a DNS alias seems to have been configured.

 

(Note that the nslookup output usually includes two IP addresses: the address of the DNS server that provided the response and the IP address that was requested. The first one would typically be the same for both queries.)

 

 

But that does not explain why a connection attempt to "bbb" fails, so there might be some other problem?

MK
Tnmkon
Occasional Collector

Re: The difference between host in connection properties and uname -a.

When I am requesting nslookup for "bbb" the output is

<...>

Trying DNS
Trying NIS
looking up FILES

<...>

And for "aaa" it's just "Trying DNS"

It means that "bbb" is in /etc/hosts and not in DNS and "aaa" is in DNS, isn't it? Is it good or bad or just is?

 


Matti_Kurkela wrote:

But that does not explain why a connection attempt to "bbb" fails, so there might be some other problem?


Maybe but I have no disadvantages from this and I have no idea what problems it may cause and how to discover it. I'm just curious user. Very curious )))

Matti_Kurkela
Honored Contributor

Re: The difference between host in connection properties and uname -a.

> It means that "bbb" is in /etc/hosts and not in DNS and "aaa" is in DNS, isn't it?

 

Exactly.

 

> Is it good or bad or just is?

 

It makes the network a bit harder to understand, so I would say it is bad.

 

Just like when you tell your workstation to connect to HP-UX named "aaa", then you log in and run "uname -a" and see "bbb" instead. Imagine being a new guy in the company, being told to "shutdown system aaa": are you sure you have logged on to the right system?

 

If you are the only person who needs to know about it, you can do anything you want... but it makes things difficult when trying to tell someone else what to do, or when troubleshooting a complex system that is built up out of several servers and applications.

MK
Tnmkon
Occasional Collector

Re: The difference between host in connection properties and uname -a.

Thank you for answering my questions! It was interesting ))