VNC and NAT

"Beerse, Corné" cbeerse "at" HISCOM.NL
Tue, 19 Mar 2002 15:49:12 +0000


> -----Original Message-----
> 
> Yes, but if the lease is up and the computer goes down or network
> connectivity is spotty, it does change.  My service changes me all the
> time and even my DHCP behind my firewall switches me from 
> time to time,
> unfortunately.  Nonetheless, it is worth a try, you are 100% 
> correct on
> the DHCP lease policies, I just found them to be unreliable in my
> application.

The formal protocol I've been told is:
Half way the lease period, the lease is extended to be-ing an entire lease
period once again
If the half-time upgrade did not succeed, there is at least one more if
there is 10% of the time left. There could be more on 20% or other
tresholds.
As long as the current lease has not been expired, the client can always
upgrade. Depending on the implementation, this can be up to 1 second before
the lease expires.

If the client dies and the server keeps running: Once the client comes back
up and does a new requrest, if the server recognizes the client, it will
provide the old, running lease. For ethernet, the recognition is on
mac-address which is global-unique. For dial-up lines, the client can be
recognized in various ways but most systems don't care or do't bother: they
just give a new lease and the old one will expire.

If there is a pool of dhcp servers, the lazy sysadmin will configure them
both as single servers with each an ip range of their own. The better
sysadmin will configure them in such a way that the runtime configuration is
distributed over the servers. Hence they all provide addresses from the same
pool and recognize old leases provide by other servers.



CBee

> 
> -----Original Message-----
> From: owner-vnc-list "at" uk.research.att.com
> [mailto:owner-vnc-list "at" uk.research.att.com] On Behalf Of Beerse, Corni
> Sent: Tuesday, March 19, 2002 1:30 AM
> To: 'vnc-list "at" uk.research.att.com'
> Subject: RE: VNC and NAT
> 
> > -----Original Message-----
> > That is correct, but as we know, the DHCP MAY change at the most
> > inconvienient times.  You can set up your DHCP server to assign
> 
> That's not true! IF a DHCP server has leased an IP address to an other
> machine, there is a lease time and a lease period. During the lease
> time,
> the client can alwasy extend the lease with the lease period. The DHCP
> server must accept this extend. Hence: once you got an IP address, you
> can
> use it forever as long as you keep extending the lease within 
> the lease
> period.
> 
> > addresses only within a certain range and then fix the IP of the VNC
> > server outside of that range.  For instance, my network 
> topology looks
> > like this:
> >
> > Other network systems:
> > Router:   192.168.1.1
> > DHCP:     192.168.1.100 - 192.168.1.254
> >
> > VNC Server:
> > IP Address:  192.168.1.10
> > Gateway:	 192.168.1.1
> > DNS:		 The DNS for your ISP.
> >
> > This always works if you have access to your DHCP configuration.  If
> > not, well then there is nothing you can do.
> >
> > Also, if your DHCP is due to your ISP on some sort of Broadband
> > connection, then I suggest TZO (www.tzo.com), they will fix an IP
> > Address to an ISP's DHCP.  But make sure that you have some sort of
> > firewall in place.
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