Understanding the network.pdf - Back to Home

The important differences between DVPs and LSPs are the following:
• LSPs only exchange link information, not routing tables the way
that DVPs do.
• LSPs only send LSA changes (such as routing updates) when an
actual change in the network occurs. DVPs send updates at a
fixed time whether changes in the network have happened or
not.
OSPF (Open Shortest Path First) is an IP dynamic routing protocol that
uses link state (Dijkstra's algorithm) as its routing algorithm.
Variable Length Subnet Mask (VLSM) Routing
One of the more complex concepts associated with IP datagram
routing is classless interdomain routing (CIDR) and the proper use of
IP subnetting and VLSM. In Chapter 2, CIDR and VLSM were
introduced. The goal here is to revisit these concepts in the context of
IP routing protocols. You should recall from Chapter 2 that the IPv4
address space can be provisioned using either the classful or classless
method:
• Classful uses natural bit mask network boundaries to define IP
networks of different sizes. There are three usable classful
network ranges: Class A, Class B, and Class C. The class of an IP
address can be determined by looking at the first 8 bits of the
binary address.
First 8 bits: Address Class Natural Network Mask
XXXXXXX Class A 255.0.0.0
01XXXXXX Class B 255.255.0.0
011XXXXX Class C 255.255.255.0
• These classful spaces can be subnetted into smaller IP subnets
to allow for more efficient use of address space. The catch is
that the major address space must be subnetted using only one
subnet mask. For example, a Class B network can be subnetted
using a Class C netmask, thereby creating 255 IP subnets, each
of which can support 254 hosts.
• Classless, as in classless interdomain routing (CIDR), is
network addressing without address classes (Class A, Class B,
and so on). Instead, IP address groups are created. These
groups can be of any size (within the limits of 32-bit address