Tag - Servers

What servers support secondary subnet numbers?

These are not complvce lists) The following servers can handle dynamic allocation on secondary subnet numbers:

  • IPTrack version 2.0
  • ISC
  • JOIN
  • SGI’s DHCP Server under IRIX 6.2
  • Cisco (previously TGV)
  • NetID
  • Microsoft Windows NT 4.0 (since service pack 2)
  • Sonic
  • QDHCP
  • ipLease
  • IBM Warp Server Version 4
  • IBM AIX

The following can serve manually allocated addresses on secondary subnet numbers:

  • IPTrack version 2.0
  • ISC
  • JOIN
  • QDHCP

The following cannot support secondary subnet numbers:

  • Microsoft Windows NT 3.51 and 4.0 (through RC1)
  • WIDE
  • Sonic DHCP Server

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how can addresses be served on subnets other than the primary one

24. If a single LAN has more than one subnet number, how can addresses be served on subnets other than the primary one?

A single LAN might have more than one subnet number applicable to the same set of ports (broadcast domain). Typically, one subnet is designated as primary, the others as secondary. A site may find it necessary to support addresses on more than one subnet number associated with a single interface. DHCP’s scheme for handling this is that the server has to be configured with the necessary information and has to support such configuration & allocation. Here are four cases a server might have to handle:

Dynamic allocation supported on secondary subnet numbers on the LAN to which the server is attached.
Dynamic allocation supported on secondary subnet numbers on a LAN which is handled through a DHCP/BOOTP Relay. In this case, the DHCP/BOOTP Relay sends the server a gateway address associated with the primary subnet and the server must know what to do with it.
The other two cases are the same capabilities during manual allocation. It is possible that a particular server-implementation can handle some of these cases, but not all of them. See section below listing the capabilities of some servers.

25. If a physical LAN has more than one logical subnet, how can different groups of clients be allocated addresses on different subnets?
One way to do this is to preconfigure each client with information about what group it belongs to. A DHCP feature designed for this is the user class option. To do this, the client software must allow the user class option to be preconfigured and the server software must support its use to control which pool a client’s address is allocated from.

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how does the DHCP server discover what subnet a request has come from

23 In a subnetted environment, how does the DHCP server discover what subnet a request has come from?

DHCP client messages are sent to off-net servers by DHCP relay agents, which are often a part of an IP router. The DHCP relay agent records the subnet from which the message was received in the DHCP message header for use by the DHCP server.

Note: a DHCP relay agent is the same thing as a BOOTP relay agent, and technically speaking, the latter phrase is correct.

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