Changing the Multihoming Property to Strict (CLI)
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 19
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
Configuring the Appliance 87
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