[c-nsp] Redundant DHCP Server

[Mohammad Khalil]

Hi peter , thanks for the great reply :)
Usually I rely on DHCPD package on Linux distributions to configure my DHCP server , but the issue is that my client wants his MLS to do that job 

Is there a way that I can remove the unused releases from the database like my case where I am using two hosts only ?
Is there a way that I can make the DHCP assign addresses for the clients in a round-robin fashion?

Thanks again

BR,
Mohammad

> Subject: Re: [c-nsp] Redundant DHCP Server
> From: peter at rathlev.dk
> To: eng_mssk at hotmail.com
> CC: cisco-nsp at puck.nether.net
> Date: Mon, 1 Jun 2015 21:07:02 +0200
> 
> Hi Mohammad,
> 
> On Mon, 2015-06-01 at 13:44 +0300, Mohammad Khalil wrote:
> > Sorry for the bad format 
> 
> You did an okay-ish job of making it better. :-) But you should probably
> consider using another mail client. Then you don't have to spend all
> that time making your emails readable.
> 
> ...
> > Now , when the clients requested IP address
> > PC1> show
> > NAME  IP/MASK            GATEWAY       MAC                LPORT  [...]
> >       192.168.10.6/24    192.168.10.3  00:50:79:66:68:01  20501  [...]
> > 
> > PC2> show
> > NAME  IP/MASK            GATEWAY       MAC                LPORT  [...]
> >       192.168.10.133/24  192.168.10.3  00:50:79:66:68:02  20502  [...]
> > 
> > R1#sh ip dhcp binding
> > Bindings from all pools not associated with VRF:
> > IP address       Client-ID/           Lease expiration       Type
> >                  Hardware address/
> >                  Username
> > 192.168.10.7     0100.5079.6668.01    Mar 01 2002 12:23 AM   Automatic
> > 192.168.10.6     0100.5079.6668.02    Mar 01 2002 12:23 AM   Automatic
> > 
> > R2#sh ip dhcp binding
> > Bindings from all pools not associated with VRF:
> > IP address       Client-ID/           Lease expiration       Type
> >                  Hardware address/
> >                  User name
> > 192.168.10.133   0100.5079.6668.01    Mar 02 2002 12:18 AM   Automatic
> > 192.168.10.132   0100.5079.6668.02    Mar 02 2002 12:18 AM   Automatic
> >  
> > I do not understand why the two servers assigned IP addresses?
> 
> This is probably "normal" for IOS. Each of the two servers offer an
> address to the client, but the client only actually ACKs one of these.
> Since the client doesn't NAK the other lease (the one it didn't take)
> the server doesn't know for certain that the lease isn't taken. (DHCP,
> being a UDP based protocol, does have some weaknesses concerning packet
> loss.)
> 
> I think "real" DHCP servers (no offense towards IOS) start by handing
> the client a shorter-than-normal lease and then hands out a full-length
> lease at the first "renew" request.
> 
> This shouldn't be a problem. If the DHCP service is supposed to be
> redundant you would have to have addresses enough for every device on
> each of the two routers anyway. Otherwise you will not have enough
> addresses if one of the fails.
> 
> More dedicated DHCP servers can coordinate their leases and avoid this
> 50% waste. But I don't think IOS is that advanced.
> 
> -- 
> Peter
> 
>