Configuring Network Routing

Language:

The system provides a single IP routing table, consisting of a collection of routing table entries. When an IP packet needs to be sent to a given destination, the system selects the routing entry whose destination most closely matches the packet's destination address (subject to the system's multihoming policy; see below). It then uses the information in the routing entry to determine what IP interface to send the packet on and, if the destination is not directly reachable, the next-hop gateway to use. If no routing entries match the destination, the packet will be dropped. If multiple routing entries tie for closest match (and are not otherwise prioritized by multihoming policy), the system will load-spread across those entries on a per-connection basis.

The system does not act as a router.

The routing table is comprised of routing entries, each of which has the following fields:

Table 19 Routing Entry Fields

Field	Description	Examples
Destination	Range of IP destination addresses (in CIDR notation) that can match the route	192.168.0.0/22
Gateway	Next hop (IP address) to send the packet to (except for "system" routes -- see below)	192.168.2.80
Family	Internet protocol	IPv4, IPv6
Type	Origin of the route	dhcp, direct, static, system
Status	Route status	active, inactive (static or direct route associated with a disabled or offline IP interface)
Interface	IP interface the packet will be sent on	igb0

A routing entry with a "destination" field of 0.0.0.0/0 matches any packet (if no other route matches more precisely), and is thus known as a 'default' route. In the BUI, default routes are distinguished from non-default routes by an additional property:

Table 20 Distinguishing Default from Non-default Routes

Kind

Route kind

Default, Network

As above, a given packet will be sent on the IP interface specified in the routing entry's "interface" field. If an IPMP interface is specified, then one of the active IP interfaces in the IPMP group will be chosen randomly on a per-connection basis and automatically refreshed if the chosen IP interface subsequently becomes unusable. Conversely, if a given IP interface is part of an IPMP group, it cannot be specified in the "interface" field because such a route would not be highly-available.

Routing entries come from a number of different origins, as identified by the "type" field. Although the origin of a routing entry has no bearing on how it is used by the system, its origin does control if and how it can be edited or deleted. The system supports the following types of routes:

Table 21 Supported Route Types

Type	Description
Static	Created and managed by the appliance administrator.
Dynamic	Created automatically by the appliance via the RIP and RIPng dynamic routing protocols (if enabled).
DHCP	Created automatically by the appliance part of enabling an IP interface that is configured to use DHCP. A DHCP route will be created for each default route provided by the DHCP server.
System	Created automatically by the appliance as part of enabling an IP interface. A system route will be created for each IP subnet the appliance can directly reach. Since these routes are directly reachable, the "gateway" field instead identifies the appliance's IP address on that subnet.
Direct	Created and managed as a network interface property: Directly Reachable Network(s). Directly reachable subnet that the local IP address is not a member of, but to which the datalink of its interface is physically connected. This improves scalability by conserving IP addresses, and could ease traffic congestion through core switches and routers.

Note that direct routes are configured as network interfaces using either the Configuration > Network BUI screen or the configuration net interfaces CLI context. Direct routes are not managed via the Routing BUI screen nor the routing CLI context.

Table 22 Routing Properties

Property	Description
Multihoming model	Controls the system policy for accepting and transmitting IP packets when multiple IP interfaces are simultaneously enabled. Allowed values are "loose" (default), "adaptive", and "strict". See the discussion below.

If a system is configured with more than one IP interface, then there may be multiple equivalent routes to a given destination, forcing the system to choose which IP interface to send a packet on. Similarly, a packet may arrive on one IP interface, but be destined to an IP address that is hosted on another IP interface. The system's behavior in such situations is determined by the selected multihoming policy. Three policies are supported:

Table 23 Multihoming Policies

Policy	Description
Loose	Do not enforce any binding between an IP packet and the IP interface used to send or receive it: 1) An IP packet will be accepted on an IP interface so long as its destination IP address is up on the appliance. 2) An IP packet will be transmitted over the IP interface tied to the route that most specifically matches an IP packet's destination address, without any regard for the IP addresses hosted on that IP interface. If no eligible routes exist, drop the packet.
Adaptive	Identical to loose, except prefer routes with a gateway address on the same subnet as the packet's source IP address: 1) An IP packet will be accepted on an IP interface so long as its destination IP address is up on the appliance. 2) An IP packet will be transmitted over the IP interface tied to the route that most specifically matches an IP packet's destination address. If multiple routes are equally specific, prefer routes that have a gateway address on the same subnet as the packet's source address. If no eligible routes exist, drop the packet.
Strict	Require a strict binding between an IP packet and the IP interface used to send or receive it: 1) An IP packet will be accepted on an IP interface so long as its destination IP address is up on that IP interface. 2) An IP packet will only be transmitted over an IP interface if its source IP address is up on that IP interface. To enforce this, when matching against the available routes, the appliance will ignore any routes that have gateway addresses on a different subnet from the packet's source address. If no eligible routes remain, drop the packet.

When selecting the multihoming policy, a key consideration is whether any of the appliance's IP interfaces will be dedicated to administration (for example, for dedicated BUI access) and thus accessed over a separate administration network. In particular, if a default route is created to provide remote access to the administration network, and a separate default route is created to provide remote access to storage protocols, then the default system policy of "loose" may cause the administrative default route to be used for storage traffic. By switching the policy to "adaptive" or "strict", the appliance will consider the IP address associated with the request as part of selecting the route for the reply. If no route can be found on the same IP interface, the "adaptive" policy will cause the system to use any available route, whereas the "strict" policy will cause the system to drop the packet.