OSPF by Abdullah Mukhtar
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This document provides an overview of a seminar presentation on Open Shortest Path First (OSPF) routing protocol. The presentation covers the basic concepts of OSPF including its use of the Shortest Path First algorithm, areas, router types, header format, and hello packets. It also gives examples of OSPF configuration and important terms like loopback interfaces, designated routers, and authentication. The summary highlights both the processor intensive nature of OSPF but also its advantages like hierarchy, link state design, and support for VLSM.
OSPF by Abdullah Mukhtar
- 1. Seminar Presenting On Open Shortest Path First (OSPF) Abdullah Mukhtar 13SCSE201018 M-TECH (CSE) BATCH -1
- 2. Overview • • • • • • • Introduction Simple basic configuration OSPF configuration Header format Important term used in OSPF Hello packet Drawback & Benefit
- 3. Introduction of OSPF 1. The OSPF protocol is a link state Protocol that handles routing for IP traffic. 2. Open Shortest Path First (OSPF) uses the Shortest Path First (SPF) algorithm, to provide a loop-free topology. 3. Open Shortest Path First (OSPF) provides fast convergence with triggered, incremental updates via Link State Advertisements (LSAs). 4. Open Shortest Path First (OSPF) is a classless protocol and allows for a hierarchical design with VLSM and route summarization. 5. The two important concepts in case of OSPF are Autonomous Systems and Areas.
- 4. Important Term Related with OSPF Loopback Interface:- A loopback interface is a logical, virtual interface on a router o Router(Config)#int loopback 2 o Router(Config-if)#ip address 200.0.0.10 255.255.255.0 Area Border Router (ABR):-An Area border router (ABR) is a router that connects one or more OSPF areas to the main backbone network. It is considered a member of all areas it is connected to. Internal Router:-An Internal Router is a router that has only OSPF neighbour relationships with routers in the same area. Backbone Router:-Backbone Routers are part of the OSPF backbone. This includes all area border routers and also routers connecting different areas. Designated Router (DR) and Backup Designated Router (BDR):-A DR is the router interface elected among all routers on a network segment, and BDR is a backup for the DR. DRs are used for reducing network traffic by providing a source for routing updates. The DR maintains a complete topology table of the network and sends the updates to the other routers via multicast. All routers in an area will form a slave/master relationship with the DR .
- 5. OSPF Areas Group of contiguous nodes/networks Per area topology DB Invisible outside the area Reduces routing traffic Backbone Area is contiguous All others areas must connect to the backbone Virtual Links Area 2 Area 3 Area 0 Backbone Area Area 4 Area 1
- 6. OSPF protocol configuration Router01(config)#interface fa0/0 Router01(config-if)#ip address 172.16.0.1 255.255.0.0 Router01(config-if)#no shutdown Router01(config)#interface s0/0 Router01(config-if)#clock rate 64000 Router01(config-if)#ip address 172.17.0.1 255.255.0.0 Router01(config-if)#no shutdown Router02(config)#interface s0/0 Router02(config-if)#ip address 172.17.0.2 255.255.0.0 Router02(config-if)#no shutdown Router03(config)#interface s0/1 Router03(config-if)#ip address 172.19.0.2 255.255.0.0 Router03(config-if)#no shutdown Continue…
- 7. OSPF protocol configuration Required Commands: Rtr(config)# router ospf process-id Rtr(config-router)#network address wildcard-mask area area-id Optional Commands: Rtr(config-router)# default-information originate (Send default) Rtr(config-router)# area area authentication (Plain authen.) Rtr(config-router)# area area authentication message-digest (md5 authen.) Rtr(config)# interface loopback number (Configure lo as RtrID) Rtr(config)# interface type slot/port (int Fa0/0) Rtr(config-if)# ip ospf priority <0-255> (DR/BDR election) Rtr(config-if)# bandwidth kbps (Modify default bandwdth) RTB(config-if)# ip ospf cost cost (Modify inter. cost) Rtr(config-if)# ip ospf hello-interval seconds (Modify Hello) Rtr(config-if)# ip ospf dead-interval seconds (Modify Dead) Rtr(config-if)# ip ospf authentication-key passwd (Plain/md5authen) Rtr(config-if)# ip ospf message-digest-key key-id md5 password
- 8. Header format of OSPF Packet 0 8 Version Type 16 31 Packet length Router Id Area Id Check sum Authentication type Authentication OSPF common header Authentication Data Fig. OSPF packet body OSPF common header precedes each OSPF Packet
- 9. Configuring a Loopback Address Rtr(config)# interface loopback 0 Rtr(config-if)# ip add 10.1.1.1 255.255.255.0 Automatically are “up” and “up” Very useful in setting Router IDs as they never go down. RouterID is used to identify the routers in the OSPF network – IP address configured with the Router-ID command – Highest loopback address – Highest active IP address Important for DR/BDR elections unless you use the ip ospf priority command Extra: Also, useful to configure “virtual” networks that you can ping and route as if they were attached networks.
- 10. The Hello Protocol When a router starts an OSPF routing process on an interface, it sends a hello packet and continues to send hellos at regular intervals ◦ The rules that govern the exchange of OSPF hello packets are called the Hello protocol ◦ Type field is set to 1 to indicate packet contains hello information
- 11. More on Hello Packets… • Hello packet timing… – sent every 10 seconds by default on broadcast multi-access and point-to-point networks – 30 seconds by default on interfaces that connect to NBMA networks, such as Frame Relay
- 12. Disadvantage and Benefit Disadvantages:OSPF is very processor intensive. OSPF maintains multiple copies of routing information, increasing the amount of memory needed. OSPF is not as easy to learn as some other protocols. Advantages:OSPF is hierarchical, using area 0 as the top as the hierarchy. OSPF is a Link State Algorithm. OSPF supports Variable Length Subnet Masks (VLSM). OSPF uses multicasting within areas.
- 13. THANK YOU
Editor's Notes
- #8: Basic Router Configure