DHCP Superscopes & how to configuring the Router ip helper-address
- From: "Gary" <gary@xxxxxxxxxxxx>
- Date: 2 Nov 2005 11:12:59 -0800
Here's a post from our Knowledge Base at
http://www.Menkaura.com/Forum/index.php for this and a lot more real
life IT solutions come along to the party. Your Knowledge is important
to us ... sharing if you can.
Regards, Gary
DHCP Considerations and thoughts
What are Superscopes?
By definition a Superscope in a administrative tool for grouping more
than one subnet together.
When a physical LAN has the requirement to accommodate more than one
subnet then Superscopes canbe used
by setting them up via the DHCP MMC.
A physical LAN that has more than one subnet is called a Multinet.
Superscopes canbe empoyed either within the same Routed network or over
diferent Router networks. So for
example a Superscope canbe used to logically group an Engineering
department together as they appear in
different buildings. Here the buidlings are likely to be on different
Routed subnets.
What is an IP Helper-address?
Used on Cisco Routers to act as a source of IP information in terms of
where to send traffic to if a
destination address is not found on the local subnet.
.... and the Cisco definition goes "Defines a helper-address for a
specified address. The helper-address defines
the selective forwarding of UDP broadcasts, including BootP, received
on the interface. The address
argument specifies a destination broadcast or host address to be used
when forwarding such datagrams."
Configuring ip helper-address(s) is undertaken as follows:
ip helper-address 192.168.2.1
or
no ip helper-address 192.168.2.1
Out of the box it will forward the following protocols:
69 TFTP, 67 BOOTP Client, 68 BOOTP Server, 37 Time Protocol, 49 TACACS,
53 DNS, 137 NetBios, 138 NetBios Datagram
Stopping IP helper-address forwarding certain default protocols is
undertaken as follows:
no ip forward-protocol udp 37
no ip forward-protocol udp 49
no ip forward-protocol udp 53
no ip forward-protocol udp 67
no ip forward-protocol udp 68
no ip forward-protocol udp 137
no ip forward-protocol udp 138
Adding other protocols:
Put your ip helper-address command on the interface that receives the
broadcasts, then in global config mode
enter the command as follows as an example:
ip forward-protocol udp 2000
.
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