IP Address Management¶
IP addressing is by nature hierarchical. The first few levels of the IPv4 hierarchy, for example, look like this:
This hierarchy comprises 33 tiers of addressing, from /0 all the way down to individual /32 address (and much, much further to /128 for IPv6). Of course, most organizations are concerned with only relatively small portions of the total IP space, so tracking the uppermost of these tiers isn't necessary.
Nautobot allows us to specify the portions of IP space that are interesting to us by defining aggregates. Typically, an aggregate will correspond to either an allocation of public (globally routable) IP space granted by a regional authority, or a private (internally-routable) designation. Common private designations include:
- 10.0.0.0/8 (RFC 1918)
- 100.64.0.0/10 (RFC 6598)
- 172.16.0.0/12 (RFC 1918)
- 192.168.0.0/16 (RFC 1918)
- One or more /48s within fd00::/8 (IPv6 unique local addressing)
Each aggregate is assigned to a RIR. For "public" aggregates, this will be the real-world authority which has granted your organization permission to use the specified IP space on the public Internet. For "private" aggregates, this will be a statutory authority, such as RFC 1918. Each aggregate can also annotate that date on which it was allocated, where applicable.
Prefixes are automatically arranged beneath their parent aggregates in Nautobot. Typically you'll want to create aggregates only for the prefixes and IP addresses that your organization actually manages: There is no need to define aggregates for provider-assigned space which is only used on Internet circuits, for example.
Because aggregates represent swaths of the global IP space, they cannot overlap with one another: They can only exist side-by-side. For instance, you cannot define both 10.0.0.0/8 and 10.16.0.0/16 as aggregates, because they overlap. 10.16.0.0/16 in this example would be created as a container prefix and automatically grouped under the 10.0.0.0/8 aggregate. Remember, the purpose of aggregates is to establish the root of your IP addressing hierarchy.
Regional Internet Registries (RIRs)¶
Regional Internet registries are responsible for the allocation of globally-routable address space. The five RIRs are ARIN, RIPE, APNIC, LACNIC, and AFRINIC. However, some address space has been set aside for internal use, such as defined in RFCs 1918 and 6598. Nautobot considers these RFCs as a sort of RIR as well; that is, an authority which "owns" certain address space. There also exist lower-tier registries which serve particular geographic areas.
Users can create whatever RIRs they like, but each aggregate must be assigned to one RIR. The RIR model includes a boolean flag which indicates whether the RIR allocates only private IP space.
For example, suppose your organization has been allocated 126.96.36.199/16 by ARIN. It also makes use of RFC 1918 addressing internally. You would first create RIRs named "ARIN" and "RFC 1918," then create an aggregate for each of these top-level prefixes, assigning it to its respective RIR.
A prefix is an IPv4 or IPv6 network and mask expressed in CIDR notation (e.g. 192.0.2.0/24). A prefix entails only the "network portion" of an IP address: All bits in the address not covered by the mask must be zero. (In other words, a prefix cannot be a specific IP address.)
Prefixes are automatically organized by their parent aggregates. Additionally, each prefix can be assigned to a particular site and virtual routing and forwarding instance (VRF). Each VRF represents a separate IP space or routing table. All prefixes not assigned to a VRF are considered to be in the "global" table.
Each prefix must be assigned a
status and can optionally be assigned a role. These terms are often used interchangeably so it's important to recognize the difference between them. The status defines a prefix's operational state. The following statuses are provided by default:
- Container - A summary of child prefixes
- Active - Provisioned and in use
- Reserved - Designated for future use
- Deprecated - No longer in use
On the other hand, a prefix's role defines its function. Role assignment is optional and roles are fully customizable. For example, you might create roles to differentiate between production and development infrastructure.
A prefix may also be assigned to a VLAN. This association is helpful for associating address space with layer two domains. A VLAN may have multiple prefixes assigned to it.
The prefix model include an "is pool" flag. If enabled, Nautobot will treat this prefix as a range (such as a NAT pool) wherein every IP address is valid and assignable. This logic is used when identifying available IP addresses within a prefix. If this flag is disabled, Nautobot will assume that the first and last (broadcast) address within an IPv4 prefix are unusable.
A role indicates the function of a prefix or VLAN. For example, you might define Data, Voice, and Security roles. Generally, a prefix will be assigned the same functional role as the VLAN to which it is assigned (if any).
An IP address comprises a single host address (either IPv4 or IPv6) and its subnet mask. Its mask should match exactly how the IP address is configured on an interface in the real world.
Like a prefix, an IP address can optionally be assigned to a VRF (otherwise, it will appear in the "global" table). IP addresses are automatically arranged under parent prefixes within their respective VRFs according to the IP hierarchy.
Each IP address can also be assigned an operational
status and a functional role. The following statuses are available by default:
- SLAAC (IPv6 Stateless Address Autoconfiguration)
Roles are used to indicate some special attribute of an IP address; for example, use as a loopback or as the the virtual IP for a VRRP group. (Note that functional roles are conceptual in nature, and thus cannot be customized by the user.) Available roles include:
An IP address can be assigned to any device or virtual machine interface, and an interface may have multiple IP addresses assigned to it. Further, each device and virtual machine may have one of its interface IPs designated as its primary IP per address family (one for IPv4 and one for IPv6).
When primary IPs are set for both IPv4 and IPv6, Nautobot will prefer IPv6. This can be changed by setting the
PREFER_IPV4 configuration parameter.
Network Address Translation (NAT)¶
An IP address can be designated as the network address translation (NAT) inside IP address for exactly one other IP address. This is useful primarily to denote a translation between public and private IP addresses. This relationship is followed in both directions: For example, if 10.0.0.1 is assigned as the inside IP for 192.0.2.1, 192.0.2.1 will be displayed as the outside IP for 10.0.0.1.
Nautobot does not support tracking one-to-many NAT relationships (also called port address translation). This type of policy requires additional logic to model and cannot be fully represented by IP address alone.
Virtual Routing and Forwarding (VRF)¶
A VRF object in Nautobot represents a virtual routing and forwarding (VRF) domain. Each VRF is essentially a separate routing table. VRFs are commonly used to isolate customers or organizations from one another within a network, or to route overlapping address space (e.g. multiple instances of the 10.0.0.0/8 space). Each VRF may be assigned to a specific tenant to aid in organizing the available IP space by customer or internal user.
Each VRF is assigned a unique name and an optional route distinguisher (RD). The RD is expected to take one of the forms prescribed in RFC 4364, however its formatting is not strictly enforced.
Each prefix and IP address may be assigned to one (and only one) VRF. If you have a prefix or IP address which exists in multiple VRFs, you will need to create a separate instance of it in Nautobot for each VRF. Any prefix or IP address not assigned to a VRF is said to belong to the "global" table.
By default, Nautobot will allow duplicate prefixes to be assigned to a VRF. This behavior can be toggled by setting the "enforce unique" flag on the VRF model.
Enforcement of unique IP space can be toggled for global table (non-VRF prefixes) using the
ENFORCE_GLOBAL_UNIQUE configuration setting.
Each VRF may have one or more import and/or export route targets applied to it. Route targets are used to control the exchange of routes (prefixes) among VRFs in L3VPNs.
A route target is a particular type of extended BGP community used to control the redistribution of routes among VRF tables in a network. Route targets can be assigned to individual VRFs in Nautobot as import or export targets (or both) to model this exchange in an L3VPN. Each route target must be given a unique name, which should be in a format prescribed by RFC 4364, similar to a VR route distinguisher.
Each route target can optionally be assigned to a tenant, and may have tags assigned to it.