User`s guide

XSR User’s Guide 73
Chapter 5 General IP Features
Configuring IP
When ICMP Mask request packets are received, the destination IP address
will be matched against the entire subnet network associated with the
primary and secondary IP addresses. The matched IP address will then be
used as the source IP address of the reply packet.
Routing Table Manager & Secondary IP
If the interface is up, each primary and secondary IP address will have an
entry in the routing table as a directly connected route. If the interface is
rejected or the IP addresses configured on it are removed, the Routing Table
Manager (RTM) will remove the corresponding route entries in the table.
If any IP address, including primary and secondaries, is deleted or changed,
any static route based on the next hop reachable through that IP address will
be removed from the active routing table. And if the IP address is restored,
any static route previously removed will be restored in the active table.
OSPF & Secondary IP
In OSPF, HELLO messagees use the primary IP address as the source address.
Adjacencies are set up based on the primary IP address only. Designated
routers (DR) and back-up DRs use the primary IP as their IP addresses. The
virtual link uses the primary IP only, as well.
OSPF can be enabled on primary and secondary IP addresses but should be
enabled on the primary address first. Also, if OSPF is used for routing, all
OSPF-enabled secondary addresses of an interface should be configured in
the same OSPF area as the primary address to function properly.
OSPF can be selectively enabled on a secondary IP address as long as it is
already enabled on the primary IP address.
RIP & Secondary IP
If RIP is used for routing, route updates should be multicast or broadcast to
each subnet represented by both the primary and secondary IP addresses.
If an interface is configured with a secondary IP address and split horizon is
enabled, route updates learned from one specific network cannot be sent back
to the same physical network. Only one routing update is sourced per
network number if split horizon is disabled.
RIP can be selectively enabled on primary and secondary IP addresses.