Amer Networks E5Web GUI - Manual (Page 361)

5.2. cOS Core DHCP Servers
cOS Core DHCP servers assign and manage the IP addresses taken from a specified address pool.
These servers are not limited to serving a single range of IP addresses but can use any IP address
range that can be specified by a cOS Core IP address object.
The DHCPServer object is used for IPv4 addresses and the DHCPv6Server object is used for IPv6
objects. The two are configured in very similar ways although the underlying implementations
are very different. The IPv6 server also provides several options which don't exist for IPv4. DHCP
relay and IP pools cannot currently be used with IPv6 DHCP.
Multiple DHCP Servers
The administrator has the ability to set up one or more logical IPv4 or IPv6 DHCP servers in cOS
Core. Filtering of DHCP client requests to different DHCP servers is based on a combination of:
• Interface
Each cOS Core interface can have, at most, one single logical DHCP server associated with it.
In other words, cOS Core can provision DHCP clients using different address ranges
depending on what interface they are located on.
• Relayer IP
The relayer IP address in the IP packet is also used to determine the server. The default value
of all-nets means that this all addresses are accepted and only the interface is considered in
making a DHCP server selection. The other options for this parameter are described further
below.
Searching the Server List
Multiple DHCP servers form a list as they are defined, the last defined being at the top of the list.
When cOS Core searches for a DHCP server to service a request, it goes through the list from top
to bottom and chooses the first server with a matching combination of interface and relayer IP
filter value. If there is no match in the list then the request is ignored.
The DHCP server ordering in the list can, of course, be changed through one of the user
interfaces.
Using Relayer IP Address Filtering
As explained above a DHCP server is selected based on a match of both interface and relayer IP
filter. Each DHCP server must have a relayer IP filter value specified and the possible values are as
follows:
• all-nets
The default value is all-nets (0.0.0.0/0). This means all DHCP requests will match this filter
value regardless if the DHCP requests comes from a client on the local network or has arrived
via a DHCP relayer.
• A value of 0.0.0.0
The value 0.0.0.0 will match DHCP requests that come from a local client only. DHCP requests
that have been relayed by a DHCP relayer will be ignored.
• A specific IP address.
Chapter 5: DHCP Services
361