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| Sendmail Saga [IV] DHCP and resolv.conf | Adding a CD recorder to Linux |
I found one annoying idiosyncracy when masquerading as hydrus.org.uk. If I "replied all" to a mail sent to user@hydrus.org.uk, the mail would fail, as the hydrus.org.uk domain was rejected as unknown by the Speedtouch router. It didn't seem to ask the ISP nameservers to resolve the domain. If I set the local domain to something other than hydrus.org.uk, the domain was accepted by sendmail. My surmise is that the DNS in the router, since it knows it can't return an A record for its own domain, returns no domain found. Sendmail takes this as gospel, and does not try the other nameservers defined in /etc/resolv.conf. While I could run with a domain of lan or some such, after I'd spent all that money, I wanted all my machines to be named correctly.
My solution was to set sendmail to masquerade as the full canonical name of the mail server, crimson.hydrus.org.uk, which could be resolved to an address by the local DNS. Not quite as clean as an unadorned domain name for the email address, but solves the problem.
This little issue had been preying on my mind, so I did a little more testing. Mailing user@hydrus.org.uk on crimson worked fine; gold was the problem. I finally realised that on crimson, I had sent up the /etc/mail/local-host-names file to define hydrus.org.uk as an alias for crimson. I just needed to do the same on gold, and the problem was solved. External addresses are now back to user@hydrus.org.uk
After I'd spend time figuring out how to put the ISP's DNS servers into the /etc/resolv.conf files on FreeBSD and Linux, I discovered a much simpler way.
The Speedtouch definition of the DHCP address pool allowed the setting of primary and secondary name servers, in addition to the default gateway. By default, these were set to the address of the router. I found you couldn't edit the DHCP pool parameters, but could only delete it. So, I deleted the DHCP pool (you have to delete any leases before you can delete the pool), and recreated it with the ISP DNS primary and secondary servers defined. Now, both UNIX machines received the full nameserver settings without any additional effort.
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