[Server-devel] Static IP and DNS problems

[David Leeming]

Thanks Tom and Martin.

At this stage I am trying to restore it to the default condition. As stated,
I tried to reverse the changes but I have ended up with the ejabberd error
and Moodle not accessible on the connected XOs.

service ejabberd status 

gives “Host name lookup failure” PPC failed on the node
ejabberd@@schoolserver: nodedown

Trying your suggestion:

With nothing connected to eth0 (unplugged)

>   dig google.com @localhost
>   dig `hostname -f` @localhost

Both give 
global options: printcmd, connection time out, no servers could be reached
(obviously)

cat /etc/resolv.conf 

##
search leemingdemo.org
172.18.0.1

The domain above is correct

What can I do to recover from the ejabberd error?

David Leeming
Leeming International Consulting, 
P.O.Box 652 Honiara, Solomon Islands
+677 7476396 (m) +677 24419 (h)
www.leeming-consulting.com


-----Original Message-----
From: Tom Mitchell [mailto:mitch at niftyegg.com] 
Sent: Wednesday, 30 June 2010 6:04 a.m.
To: Martin Langhoff
Cc: David Leeming; XS Devel
Subject: Re: [Server-devel] Static IP and DNS problems

On Tue, Jun 29, 2010 at 9:34 AM, Martin Langhoff
<martin.langhoff at gmail.com> wrote:
> On Tue, Jun 29, 2010 at 1:43 AM, David Leeming
> <david at leeming-consulting.com> wrote:
>> I tried to set up the WAN interface with a static IP address and DNS
>> pointing at the gateway, following instructions at
>
> It is all pretty straightforward -- but "and DNS pointing at the
> gateway" sounds suspicious. Where did you add that "dns pointing at
> the gateway"?
>

Tell us more about the local site setup.

DNS at the gateway is common in a DHCP world especially
behind a NAT router.  It should be possible to see what
name servers the NAT router or Gateway is connected to
by connecting to the configuration tool and then test them
with "dig" or "host".   Another tool "traceroute" can let you
see if you have connectivity to the name server.   A static
address must not be in the DHCP servers pool of addresses.


>> What should I be looking for?
>
>  - Is bind running correctly on the XS? To understand this... - are
> there any interesting msgs in /var/log/messages.log from named ? Do
> the following commands work... (executed on the XS)
>
>   dig google.com @localhost
>   dig `hostname -f` @localhost
>
>  - Is /etc/resolv.conf correctly pointing to the named running on the XS?
>

Two interesting google hosts are public name servers:
$ host 8.8.8.8
8.8.8.8.in-addr.arpa domain name pointer google-public-dns-a.google.com.
$ host 8.8.4.4
4.4.8.8.in-addr.arpa domain name pointer google-public-dns-b.google.com.

These name servers can be used on a command line:
$ host www.google.com 8.8.8.8
Using domain server:
Name: 8.8.8.8
Address: 8.8.8.8#53
Aliases:

www.google.com is an alias for www.l.google.com.
www.l.google.com has address 74.125.19.104
www.l.google.com has address 74.125.19.103
www.l.google.com has address 74.125.19.147
www.l.google.com has address 74.125.19.99


N.B. that localhost is not resolved by google.
This can be important and is commonly solved
by /etc/hosts and placing a host reference in
host.config.

So, do check /etc/host.config  you can have the local
file /etc/hosts inspected by the resolver code first
by setting placing hosts as the first tool in
the resolver line and follow that with DNS ( bind )
   $ cat /etc/host.conf
   multi on
   order hosts,bind

This lets your localhost line in /etc/hosts be seen.
It also lets you name hosts on the inside of a
NAT that uses private networks.
   192.168.0.0 – 192.168.255.255
   172.16.0.0 – 172.31.255.255
   10.0.0.0 – 10.255.255.255
      and watch for the zero configuration IP address space....
  169.254.0.0/16 as described in RFC 3927

http://en.wikipedia.org/wiki/Private_network

Private networks are interesting.   They cannot
be auto routed and there is no global reverse
lookup

Name servers  for private networks are interesting.
They are a couple cases, the ``easy'' one is
where all the network is routed and no private
networks are involved.   Private networks are
more interesting because outside of the private
network a ``smart'' router's address is returned
while inside local private network numbers are
returned.

Debugging requires knowing if private net numbers
are being used and if the name server is returns
two views one for outside lookup and another
of inside lookups.  Netmasks?? this is another
topic of interest.   Netmasks establish broadcast
conventions that are important for many services.

One tactic is to take advantage of local /etc/host
resolution and fill in many of the interesting lookups by hand while
debugging a name server.  Once the debugging is
finished comment out or delete the hand made edits
to avoid future confusion (important).

An XS server can sit inside or on the edge of
a local network so the local decisions for setting
up a network environment can be important.



> hth,
>
> m
> --
>  martin.langhoff at gmail.com
>  martin at laptop.org -- School Server Architect
-- 
        T o m   M i t c h e l l
        mitch-at-niftyegg-dot-com