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Re: Public Use VLAN (x-posted to netman listserv)
From: Aaron Hockett <AHockett () WARNERPACIFIC EDU>
Date: Tue, 2 Oct 2012 20:49:50 -0700


Good read.  How are you handling DHCP on what I'm assuming is your core firewall that keeps the public away from the 
private?  We're facing a similar push and I'm looking at moving all resnet and wireless to a "public" vlan that just 
dumps it to the net with public DNS (Google or Century link) but I'm looking for suggestions on how to handle DHCP off 
a single public IP via NAT.


Warner Pacific College
Network Engineer 

Jeff Kell <jeff-kell () UTC EDU> wrote:

You have a couple of options. 

What we do is have split DNS (our inside network is RFC1918, outside is
public, only public servers are on our external DNS).  The external
nameservers technically live inside our firewall/IPS/etc protection, so
they're "on-campus".  We can point guest/etc "outside" users at the
external DNS, and they get "outside" IPs for any internal resources, so
they "hair-pin" out to the edge and back through the firewalls to gain
access (we also ACL block direct).

It sounds like you have uniform DNS.  You can still point them there,
allow their range recursive access, but be careful that you don't do
"DNS inspection" on that traffic or they'll get converted back to
private inside addresses.

If you have true internal vs external DNS, this is much easier to swing
that trying to make a uniform one "dual personality"  :)

If you have them using public DNS (I don't know if you are referring to
"your" public DNS, or a 3rd-party "public" DNS) they should be getting
outside IPs, and it's just a matter of allowing their range to hair-pin
back through the firewall (you may need to loop through your edge/border
if you don't allow same-interface traffic).  Or are  you "wanting" them
to get internal IPs?  In the latter case you might reinstate the DNS
inspection / NAT rewrites, but again, be careful with the
split-personality roles.


On 10/2/2012 9:56 PM, Allen Wood wrote:

As much as I hate it, I've been told to setup an open wireless network
for our campus.  I created a vlan with access lists that deny  all
traffic to inside our network, and created the open SSID to put on
it.  Traffic can flow freely now from the open wireless to the internet.


However, I'm using a public DNS for the clients and they're unable to
reach our locally hosted (NAT'd) web servers.  We're currently using a
Cisco ASA at the edge of our network which does all of our NAT'ing.  I
could open up the VLAN access list a bit and allow them access to our
internal DNS & web servers, but I'd rather not.


Has anyone run into this issue before?  What's the "best practices" at
this point... other than removing the public network in the first place! 


Thanks in advance,




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