Extreme Networks ExtremeWare XOS Guide Manual page 505

Route Manager
The Route Manager will install a route corresponding to each of the secondary interfaces. The route
origin will be direct, will be treated as a regular IP route, and can be used for IP data traffic forwarding.
These routes can also be redistributed into the various routing protocol domains if you configure route
redistribution.
IRDP
There are some functional changes required in Internet Router Discovery Protocol (IRDP) as result of IP
multinetting support. When IRDP is enabled on a Layer 3 VLAN, ExtremeWare XOS periodically sends
ICMP router advertisement messages through each subnet (primary and secondary) and responds to
ICMP router solicitation messages based on the source IP address of soliciting host.
Unicast Routing Protocols
Unicast routing protocols treat each IP network as an interface. The interface corresponding to the
primary subnet is the active interface, and the interfaces corresponding to the secondary subnet are
passive subnets.
For example, in the case of Open Shortest Path First (OSPF), the system treats each network as an
interface, and hello messages are not sent out or received over the non-primary interface. In this way,
the router link state advertisement (LSA) includes information to advertise that the primary network is
a transit network and the secondary networks are stub networks, thereby preventing any traffic from
being routed from a source in the secondary network.
Interface-based routing protocols (for example, OSPF) can be configured on per VLAN basis. There is no
way to configure a routing protocol on an individual primary or secondary interface. Configuring a
protocol parameter on a VLAN automatically configures the parameter on all its associated primary and
secondary interfaces. The same logic applies to configuring IP forwarding, for example, on a VLAN.
Routing protocols in the multinetted environment advertise the secondary subnets to their peers in their
protocol exchange process. For example, for OSPF the secondary subnets are advertised as stub
networks in router LSAs. RIP also advertises secondary subnets to its peers residing on the primary
subnet.
OSPF. This section describes the behavior of OSPF in an IPv4 multinetting environment:
Each network is treated as an interface, and hello messages are not sent out or received over the non-
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primary interface. In this way, the router LSA includes information to advertise that the primary
network is a transit network and the secondary networks are stub networks, thereby preventing any
traffic from being routed from a source in the secondary network.
Any inbound OSPF control packets from secondary interfaces are dropped.
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Direct routes corresponding to secondary interfaces can be exported into the OSPF domain (by
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enabling export of direct routes), if OSPF is not enabled on the container VLAN.
When you create an OSPF area address range for aggregation, you must consider the secondary
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subnet addresses for any conflicts. That is, any secondary interface with the exact subnet address as
the range cannot be in another area.
The automatic selection algorithm for the OSPF router ID considers the secondary interface
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addresses also. The numerically highest interface address is selected as the OSPF router-id.
ExtremeWare XOS 11.3 Concepts Guide
IPv4 Multinetting
505