Is it possible on Cisco 3640 to redirect all DNS requests to a certain DNS
server?  I have a large number of users trying to use a couple DNS servers
that are now gone due to a backbone change.  I want to redirect any UDP port
53 packets coming in the ethernet interface to a DNS server at 12.127.16.69
or AT&T DNS server.  I imagine it should be setup so any DNS requests going
to the backup server 12.127.17.72 should be untouched.  Is this possible?

Matt

In article <vv64irbh9rq42d@corp.supernews.com>,
Matt <nospam.hciss@yahoo.com> wrote:
:Is it possible on Cisco 3640 to redirect all DNS requests to a certain DNS
:server?  I have a large number of users trying to use a couple DNS servers
:that are now gone due to a backbone change.  I want to redirect any UDP port
:53 packets coming in the ethernet interface to a DNS server at 12.127.16.69
:or AT&T DNS server.  I imagine it should be setup so any DNS requests going
:to the backup server 12.127.17.72 should be untouched.  Is this possible?

I was going to suggest Policy Based Routing (PBR), but PBR would
only allow you to change the interface and "next hop"; with the
new DNS server being more than one hop away from you, the next router
would re-write the next-hop anyhow.

What you will need, then, is to use NAT with the "inside" set to
the WAN interface and the "outside" set to the local interface.
Reversing the usual roles of "inside" and "outside" allows you to
rewrite destination addresses (NAT usually rewrites source addresses
on departing packets.)

I know this can sound like an awful kludge, but it is perfectly
valid. On PIX this is known as "outside NAT" (these days) or
"bidirectional NAT". The older way of doing things on PIX would have
been to use "alias", which I don't recall has any IOS equivilent.
-- 
   "No one has the right to destroy another person's belief by
   demanding empirical evidence."            -- Ann Landers