About the routing table

What the routing table contains

The routing table contains the current routes that have been established and are currently in use, as well as the default route specification.

Default route setup in Data ONTAP

Data ONTAP uses a default route entry to route to destinations that it does not explicitly know about in its routing table. You can set the default route in Data ONTAP either during the initial setup or later by modifying the /etc/rc file.

If you are upgrading your storage system to this Data ONTAP release and currently use the /etc/dgateways file to set a default route, you should now use the /etc/rc file, router discovery, or Routing Information Protocol (RIP) instead. The /etc/dgateways file was deprecated in Data ONTAP 6.0 (that is, it is still supported for backward compatibility but its use is not recommended).

Example

The following sample /etc/rc file shows the route add command used to add a default route:

hostname tpubs-f720

ifconfig e0 172.28.50.21 netmask 255.255.255.0 mediatype 100tx-fd

route add default 172.28.50.1 1

routed on

Managing the routing table

You can manage the routing table in two ways:

Automatically, using the routed daemon
The routed daemon is enabled by default.
Manually, using the route command

The routing table might also be modified when one of the following occurs:

A new interface is configured with the ifconfig command and there are no existing entries for the new network number in the routing table.
Your storage system receives an ICMP redirect packet with notification of a better first-hop router for a particular destination.
Your storage system is rebooted after the default route in the /etc/rc file is modified.

What the routed daemon provides

The routed daemon enables these functions:

Deletion of redirected routes after a specified period
Router discovery with Internet Router Discovery Protocol (IRDP), which is useful only if there is no static default route
Listening for RIP packets
Migration of routes to alternate interfaces when multiple interfaces are available on the same subnet

In addition, routed can be configured to

Control RIP and IRDP behavior
Generate RIP response messages that update a host route on your storage system
Recognize distant gateways identified in the /etc/gateways file

For more information about routed, see the na_routed(1) man page.

When the routed daemon can be turned off

In some circumstances, it might be desirable to turn the routed daemon off. For example, if you have multiple interfaces on the same subnet and you want to direct network traffic to specific interfaces, you must turn routed off because routed sees all interfaces on a subnet as equivalent.

You can safely turn off routed if you

Do not use RIP or router discovery (they can be disabled by setting values in the /etc/gateways file)
Have a single router per subnet or a network in which redirects are not sent
Are able to manage your routing table directly
Note
Unless you have specific routing needs and you understand network routing configuration, you are advised to always keep routed on, even if you do not want Data ONTAP to make routing decisions based on routing updates. Turning routed off could cause unexpected routing behavior in Data ONTAP.

Routing tables in a vFiler unit environment

If you enable the MultiStore® license, Data ONTAP disables the routed daemon. Therefore, routing tables in a vFiler^TM unit environment must be managed manually with the route command.

All vFiler units in an IPspace (the IP address space in which vFiler units can function) share a routing table. Therefore, any commands that display or manipulate the routing table apply to all vFiler units in that IPspace.

For more information, see the section on network considerations in the Data ONTAP 7.1 MultiStore Management Guide.