When using additional addresses for features like NAT or binding services to different interfaces, you can add extra addresses to already defined interfaces using Virtual IPs.
Types and their usage
Ixolate supports different types of virtual addresses all with their specific purposes, which we will explain below.
IP Alias
A standard extra address, which you can use to bind services to or use in NAT rules.
The address will act like a normal interface address, which means it will respond to ICMP ping requests and will generate ARP traffic (OSI layer 2).
Additionally you can add an alias into an existing CARP group (by setting its VHID). See the CARP VIP type below for more information.
Usually the subnet mask should match the interfaces or be defined as a single address (/32 or /128).
CARP
Specifies an address for use in a high availability cluster, acts like a regular address when the node is in MASTER state.
A VHID Group number must be specified. The “Select an unassigned VHID” button allows you to automatically select an available VHID number. The usual approach to selecting a VHID is to use a different number per interface, but this is not a strict requirement, since the underlying protocol only requires a VHID to be unique within the broadcast domain of the specified interface. However, to ease management and debugging it is recommended to keep a separate VHID per interface.
Internally a custom mac address is generated needed for the protocol. More information about CARP can be found in our high availability section.
Combining CARP virtual IP types with IP aliases
In cases where there is a need for multiple IP aliases on a single interface which should be shared by a CARP cluster, you can assign a single CARP VIP with a specific VHID in combination with regular IP alias types, setting the VHID field to the same number as the initial CARP VIP VHID:
- The entire set of configured virtual IP addresses are now considered a single host (VHID).
- Only this VHID will send out advertisement packets.
- The set of IP addresses for this VHID are hashed and inserted in the advertisement packets. This hash is compared to the same VHID hash on the peer on reception of CARP advertisements. If they do not match, the peer will assume the master role as the configuration is out of sync.
Proxy ARP
Does not add a real address to an interface, instead it will use choparp to reply to arp requests on the network. This can sometimes be practical in situations where clients should be let to believe an address is local.
Settings
The interface should validate suitable combinations of settings, below you will find a detailed explanation for everyone of them.
| Mode | The type of address, as defined in Types. |
| Interface | The interface this address belongs to. |
| Type | Either Network or Single address, only has affect when creating NAT rules, where Proxy ARP combined with Expansion will generate separate addresses for all items in the netmask. |
| Address | The address and netmask to assign, when assigning multiple addresses in the same network, the masks usually should match. |
| Deny service binding | Assigning services to the virtual IP’s interface will automatically include this address. Check to prevent binding to this address instead. |
| Peer (ipv4, ipv6) | (Ixolate version >= 24.7) CARP Destination address to use when announcing, defaults to multicast, but can be configured as unicast address when multicast can not be used (for example with cloud providers) |
| Gateway | Only applies to IP Alias types, usually this field should be empty, except some tunnel devices (ppp/pppoe/tun) expect the gateway address to be defined. |
| Disable Expansion | Disable expansion of this entry into IPs on NAT lists (e.g. 192.168.1.0/24 expands to 256 entries). |
| Virtual IP Password | The password used to encrypt CARP packets over the network, should be the same on preferred master and backup node(s). |
| VHID Group | The Virtual Host ID. This is a unique number that is used to identify the redundancy group to other nodes in the group, and to distinguish between groups on the same network. Acceptable values are from 1 to 255. This must be the same on all members of the group. |
| Advertising Frequency | Defines how often is advertised that this interface is part of a group (Base defined in seconds) and how much to skew when sending advertisements. A higher skew means less preferred. |
| Description | User friendly description of this VIP |
Status
The status page shows all configured carp VHID groups and their active status. Our status screen also offers some buttons to disable carp or force a node into maintenance mode.
All different statuses are detailed below.
INIT
Usually this indicates there is an issue with the interface, often this relates to not disconnected interfaces or other technical problems.
BACKUP
In backup state this interface is part of a cluster and listening to advertisements. If for some reason it won’t receive advertisements for a short period of time, it will transition to master.
MASTER
Marks the active node, while listening to advertisements seen on the network. If another node is seen with a better advertisement it might transition to backup (depending on preempt setting, found on the System › High Availability › Settings page).
DISABLED
Displayed when Temporarily Disable CARP is clicked on this page.