The cOS Core Address Book contains named objects representing various types of IP addresses, including single IP addresses, networks as well as ranges of IP addresses. Ethernet MAC addresses can also be defined in the address book.
IP Address objects are used to define symbolic names for various types of IP addresses. Depending on how the address is specified, an IP Address object can represent either a single IP address (a specific host), a network or a range of IP addresses and even a DNS name.
Ethernet Address objects are used to define symbolic names for MAC addresses. This is useful, for example, when populating the ARP table with static ARP entries or for other parts of the configuration where symbolic names are preferred over numerical Ethernet addresses.
Address objects can be grouped in order to simplify configuration. Consider a number of public servers that should be accessible from the Internet. The servers have IP addresses that are not in a sequence, and can therefore not be referenced to as a single IP range. Consequently, individual IP Address objects have to be created for each server. Instead of having to cope with the burden of creating and maintaining separate filtering policies allowing traffic to each server, an Address Group named, for example web-servers, could be created with the web server hosts as group members. Now, a single policy can be used with this group, thereby greatly reducing the administrative workload.
You can exclude IP addresses from address group. For example, if a network object is the network 192.168.2.0/24 and this is added to a group, it is possible to then explicitly exclude the IPv4 address 192.168.2.1. This means that the group will then contain the range 192.168.2.2 to 192.168.2.255.
Address Group objects are not restricted to contain members of the same subtype. IP host objects can be teamed up with IP ranges, IP networks , with DNS names and so on. All addresses of all group members are then combined by cOS Core, effectively resulting in the union of all the addresses.
Auto-Generated Address Objects
To simplify the configuration, a number of address objects in the address book are automatically created by cOS Core when the system starts for the first time and these objects are used in various parts of the initial configuration. The following address objects are auto-generated – Interface addresses, default gateway address, all-nets object (0.0.0.0/0)
Address Book Folders
In order to help organize large numbers of entries in the address book, it is possible to create address book folders. These folders are just like a folder in a computer’s file system. They are created with a given name and can then be used to contain all the IP address objects that are related together as a group. Using folders is simply a way for the administrator to conveniently divide up address book entries and no special properties are given to entries in different folders. cOS Core continues to see all entries as though they were in a large table of IP address objects. The folder concept is also used by cOS Core in other contexts such as IP rule sets, where related IP rules can be grouped together in administrator created folders.