Specifications
62 Implementing IBM System Networking 10Gb Ethernet Switches
When a router receives a routing update that includes changes to an entry, it updates its
routing table to reflect the new route. The metric value for the path is increased by 1, and the
sender is indicated as the next hop. RIP routers maintain only the best route (the route with
the lowest metric value) to a destination.
RIPv1
RIP version 1 use broadcast User Datagram Protocol (UDP) data packets for the regular
routing updates. The main disadvantage is that the routing updates do not carry subnet mask
information. Hence, the router cannot determine whether the route is a subnet route or a host
route. RIPv1 is of limited usage after the introduction of RIPv2. For more information about
RIPv1 and RIPv2, see RFC 1058, found at:
http://www.ietf.org/rfc/rfc1058.txt
RIPv2
RIPv2 is the most popular and preferred configuration for most networks. RIPv2 expands the
amount of useful information carried in RIP messages and provides a measure of security.
For a detailed explanation of RIPv2, see the following RFCs:
RFC 1723, found at:
http://www.ietf.org/rfc/rfc1723.txt
RFC 2453, found at:
http://www.ietf.org/rfc/rfc2453.txt
RIPv2 improves efficiency by using multicast UDP (address 224.0.0.9) data packets for
regular routing updates. Subnet mask information is provided in the routing updates. A
security option is added for authenticating routing updates, by using a shared password.
2.3.4 Open Shortest Path First
Open Shortest Path First (OSPF) is designed for routing traffic within a single IP domain
called an Autonomous System (AS). The AS can be divided into smaller logical units known
as
areas.
All routing devices maintain link information in their own Link State Database (LSDB). The
LSDB for all routing devices within an area is identical, but is not exchanged between
different areas. Only routing updates are exchanged between areas, reducing the impact for
maintaining routing information on a large, dynamic network.
OSPF area types
An AS can be broken into logical units known as areas. In any AS with multiple areas, one
area must be designated as area 0, known as the
backbone. The backbone acts as the
central OSPF area.
All other areas in the AS must be connected to the backbone. Areas inject summary routing
information into the backbone, which then distributes it to other areas as needed.