1. An OSPF area is a collection of networks and routers that has the same area identification.
2. The following are the types of OSPF routers:
3. LSA Types:
4. The sequence of steps followed in OSPF operation are as below:
5.The command "show ip ospf database" displays the contents of the topological database maintained by the router. This command also displays router id and the ospf process id.
6.show ip ospf interface can be used to check whether the interfaces have been configured properly. The command also gives the timer intervals, including hello intervals, and neighbor adjacencies.
7.OSPF keeps up to six equal-cost route entries in the routing table for load balancing.
8.OSPF uses Dijkstra algorithm to calculate lowest cost route. The algorithm adds up the total costs between the local router and the each destination network. The lowest cost route is the preferred route when there are multiple paths to a given destination.
9. OSPF has the following advantages over Distance Vector protocols such as RIP:
10. The path cost in OSPF network is calculated using bandwidth. The formula used is [10 <8> divided by Bandwidth]. For example, the cost of a 56kbps serial link is 1785. The default cost of a 10mbps Ethernet is 10.
22. When a serial line is configured on a Cisco router, the default bandwidth is 1.544Mbps. If the line is slower speed, "bandwidth" command can be used to specify the real link speed. The cost of the link will then automatically correspond to the changed value.
23. You must manually configure a static route to configure DDR (Dial on Demand Routing). DDR is widely used as a backup route, in case of failure of primary link.
24. Route Summarization:
Route summarization is calculated as below:
1. Take the first IP: 172.24.54.0/24: 172.24. 0 0 1 1 0 1 1 0.0
2. Take the second IP: 172.24.53.0/24: 172.24. 0 0 1 1 0 1 0 1.0
Note that we are not really concerned about the octets that have equal decimal values. This is because they donít come into play while calculating summarization route, in this case.
Count the number of bits in the third octet that are aligned
(or lined up) with same values. In this case 6 bits are lined up
in the third octet. The summarization route is calculated by adding
this number (6) to the octets preceding the third (first and second
Therefore, the number of bits in the summarized route is 8+8+6 = 22
Calculate the decimal equivalent for third octet with 6 bits
as given in the matching binary. That is 0 0 1 1 0 1 x x. Note x
is because it corresponds to non matching binary number. It is equal
to 128*0 + 64*0 + 32*1 + 16*1 + 8*0 + 4*1 or 32+16+4 or 52.
Therefore, the summarized route is:
25. While evolving a network addressing scheme for an organization, you need to assign a different network number for each subnet. Also, you need to set aside one network number for each WAN connection.
26. Representing a subnet mask with / notation:
Consider an IP subnet mask of 255.255.255.128. The same be represented as /25. This is arrived at, by taking the binary equivalent of 255.255.255.128 (= 11111111.11111111.11111111.10000000). Count the number of ones', there are 25 of them. Therefore, the same can be written as /25.
27. The following are link state routing protocols:
28. OSPF - LSA, LSR, and LSUs:
1. LSA (Link State Advertisement): LSAs are included in the database description packets (DDPs or DBDs). LSA entries include link-state type, the address of the advertising router, the cost of the link, and the sequence number.
2. LSR ( Link State Request): When a slave router receives a DDP (Database Description Packet), it sends an LSAck packet. Then it compares the received information with its own information. If the DDP has more recent information, the slave router sends a link-state request (LSR) to the master router.
3. LSU ( Link State Update): LSU packet is sent in response to LSR (Link-State Request) packet that is sent from a slave router to a master router. LSU contains complete information about the requested entry.
4. In an OSPF environment,
29. Important features of stub area are:
Some of the important terms used in Enhanced IGRP are: