User`s guide

XSR User’s Guide 83
Chapter 5 IP Routing Protocols
Configuring IP
 LOCAL 10
 STATIC 9
 OSPF INTRA 7
 OSPF_INTER 6
 OSPF_EXT 4
 PREF_RIP 4
Default Network
The default network is used to specify candidates for the default route when a
default route (0.0.0.0) is not specified or learned. If the network specified by
the
ip default-network command appears in the routing table from any
source (dynamic or static), it is flagged as a candidate default route and is
subject to being chosen as the default route for the XSR.
You may enter
ip default-network multiple times. All candidate default
routes appear in the routing table preceded by an asterisk. If the network
specified is a subnet, default routing applies only to the classfull network. If a
directly connected interface is specified, RIP will generate a default route.
If the XSR has no interface on the default network, but it has a route to it, it
will consider this network as a candidate default route for itself. Route
candidates will be examined and the best one chosen based on administrative
distance and metric.
The gateway to the best default path will be named the gateway of last resort
for the router. The gateway of last resort is the gateway for the route used by
packets as the last possible alternative, when there is no route to the
destination, including a default route.
Refer to the XSR CLI Reference Guide for more information and a sample
default route configuration.
Classless Inter-Domain Routing (CIDR)
CIDR is an advanced addres scheme for the Internet allowing more efficient
allocation of IP addresses than the earlier A, B, and C address scheme. CIDR
currently uses prefixes anywhere from 13 to 27 bits. This allows for address
assignments that much more closely fit an organization's specific needs.