[TriLUG] dhcp relay question

[Ryan Leathers]

Using Linux (or some other host) may not be the right choice.

Most routers today can serve DHCP directly.  Apart from the obvious
benefit of using what's already there... there may be a compelling
requirement for dynamic DNS or WINS. In such circumstances folks have
often been sticking with DHCP forwarding rather than getting leases
directly from the router or from a PC host running a dhcpd.  

In the past couple of years it has become more common for routers with
DHCP Server functionality to share the bindings database with a host
somewhere on the network.  This neat trick gives you local address
leases (in case you are at a branch office for example) and also keeps
the lease information synchronized with the network services that need
it like dynDNS and WINS.

On a Cisco router this is accomplished with the command:
Router(config)# ip dhcp database url 

Perhaps there is a dhcpd available for Linux that can do the same
thing.  In any case, determine whether or not you need to synchronize
the bindings database before getting too far into an implementation. 

Ryan 


On Tue, 2003-05-13 at 09:52, John Beimler wrote:
> Chris Hedemark wrote:
> 
> >On Tuesday, May 13, 2003, at 08:43 AM, Mike Johnson wrote:
> >  
> >
> >>Yes.  DHCP is ethernet broadcast, which is not repeated by layer 3
> >>(routers) devices (normally), only layer 2 (switches/hubs).  If you
> >>set your routers to relay DHCP, they'll do what you want.
> >>    
> >>
> >
> >Note that most Cisco devices allow you to enable a DHCP helper to have 
> >a client on one network use a DHCP server on another.  It works pretty 
> >well in a LAN environment but I wouldn't trust it over WAN (WAN link 
> >goes down, suddenly DHCP leases aren't renewing and you can't even get 
> >  
> >
> >to the local resources).
> >
> 
> We use it here, our DHCP server is in Florida, over a fractional T1.  
> Getting a DHCP lease take about a minute on a good day, if you try when 
> our bandwith is saturated, it can take five minutes.  And as Chris 
> stated, when the WAN link dies, your stations with DHCP are a pain to 
> reconfigure so you can use them. Linux/BSD DHCP servers are easy to set 
> up, I'd just put in a small one at every site, it will make life easier.
> 
> Peace.
> 
> john
> 
> 
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