Priscilla Oppenheimer wrote: > > p b wrote: > > Actually using secondaries and DHCP should be a non issue with > > any reasonable DHCP server platform. As you mention, in many > > versions of IOS the interface's primary IP address is used > > as the DHCP giaddr. If an interface has multiple secondaries, > > one just needs to configure the DHCP server to be aware that > > there are multiple scopes associated with the giaddr. > > But how does the server know which scope to use for the > incoming requests when they all have the same giaddr? > > Priscilla
Well, if you're going to put secondaries on an interface (physical or sub-interface), one could make the assumption that all relayed DHCP requests from that interface should be treated equally. Which means when the DHCP server gets the DHCP request, looks at the giaddr, sees there are multiple scopes associated with the giaddr, all of which *may be* applicable, and then assigns an IP address from one of the scopes to the end device. Now, if you wanted to segment end-users by function to a particular subnet, one could use sub-interfaces and then VLAN tag ports on the switch to correlate sub's traffic to a particular sub-interface. That's fine. But if you've initially assigned a /25 to the sub-interface and now need to grow it, you've got two options: a) replace the primary subnet with a larger block, which means replacing the primary on the sub-interface, renumber all the users, and update the DHCP server, or b) add a secondary block onto the sub-interface and then define a second scope on the DHCP server and related it back to the primary scope. Using this approach, there's no need to renumber. And if you find out you need to support 180 users, you could drop in a /26 to complement the /25. While you're making the changes, there's no impact to existing users on the interface. If you go option a), you'll need a /24 and lose some addressing efficiency. Option "b)" seems the way to go, but requires that the DHCP server support the concept of relating secondary scopes back to a primary. CNR supports this mechanism via the "primary-scope" construct. If your interface looks like: scope_10.0.1.0: scope details scope_10. Now, if one had secondaries on an interface (or sub-int) and wanted to vector a device (or particular types of devices) to a particular secondary, one needs to provide the DHCP server with more information. A sub-interface doesn't help There might be information supplied in the DHCP packet by the client to help identify the type of device, or DHCP information might be inserted by the Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=58541&t=58498 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
