www. CNAME

Glen Turner glen.turner at aarnet.edu.au
Thu Nov 18 03:43:19 UTC 1999

Barry Margolin wrote:

> There's no problem with having sub as a CNAME.  It's a subdomain, but it's
> *not* a subzone, so it doesn't violate the rule against CNAME and other
> data.  We do this extensively for the domain that contains all our routers;
> we have A records for each interface, and then a CNAME record for the
> router's name with no interface prefix:

We use the router's loopback interface address as the name
of the router.  Cisco lets you set the source address or
router orginated packets to the loopback interface.

This has three nice effects:
 - you don't hit resolver library limits on routers
   with hundreds of interfaces (VLANs make this really
   easy to do).
 - syslog and SNMP records are consistently stamped
   no matter what the network topology.
 - puting all the loopback interfaces into one IP address
   range makes verification of source addresses for
   routing updates and the like very simple and
   consistent across all routers.

If possible, make the loopback interfaces use the highest
addresses as the highest address in the system is often used
as the router ID by default by various routing protocols.

$ORIGIN gigabit0-0-0.adelaide5sa.net.example.com.
vlan0002    IN   A   ....
vlan0034    IN   A   ....
$ORIGIN net.example.com.
adelaide5sa IN   A   ....

 Glen Turner                                 Network Engineer
 (08) 8303 3936      Australian Academic and Research Network
 glen.turner at aarnet.edu.au          http://www.aarnet.edu.au/

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