OSPF in a Nutshell

Below are some of the OSPF edges/pros as compared to contemporary protocols of the same age:

  • No hop count limitations as in other contemporary protocols
  • OSPF allows summarization with almost all possible scenarios
  • Recognizes VLSMs (variable-length subnet masks)
  • No Broadcasts … OSPF uses multicasts 224.0.0.5, 224.0.0.6
  • OSPF converges much faster than RIP, because OSPF propagates changes immediately.
  • Load balancing up to 6x equal cost paths
  • OSPF is a Secure Protocol (Multiple authentication options available)
  • OSPF allows for tagging of external routes injected by other AS
  • OSPF is CPU/Memory intensive especially in multi-area and multi-process scenarios
  • Summarization can be done only on ABR & ASBR router not on all routers
  • OSPF is heirarchical, using area 0 as the top as the hierarchy
  • OSPF provides fast convergence with triggered, incremental updates via LSAs
  • OSPF is a classless protocol and allows for a hierarchical design with VLSM and route summarization
  • OSPF requires more memory to hold the adjacency (list of OSPF neighbors), topology and routing tables

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Waqas Karim is a seasoned Network Expert … Geek. He is the founder of ATech. ATech was started for learning & sharing. Over time the platform has grown to include other resources which continue to attract fellow networkers. Today it sees upward trend of a hundred thousand visitors per month, scattered all over the globe. His specialty is networking, but his interest & expertise spans from traditional IT to Network Security including Programming, Virtualization, Service Provider & so on... no matter the badge on the box. He is CCIE Certified (CCIE#56732) in addition to below badges: Telecom Engineer (BE) + CCIE-RS (CCIE#56732) + Huawei Certified (HW#706632) + MBA Microsoft Certified MCITP, MCSE#109*26, CCNP-Sec, CCNP-SP, CCNA-DC, CompTIA Security+, Nokia NRS-I, JNCIA, ITIL Certified (ITIL#*6373), CEH (Certified Ethical Hacker).

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Henry
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Henry

Excellent post!!
and Thanks for your answers to all questions.

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Guide Hadden
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Guide Hadden

OSPF is Destination based or Source based Protocol?

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Waqas Karim
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Waqas Karim

OSPF is a Destination based Protocol.
OSPF routes IP packets based solely on the destination IP address found in the IP packet header. IP packets are not encapsulated in any further protocol headers as they transit the AS. OSPF uses Port IP Port 89 for Transport. It uses its own transport, not TCP/UDP.

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Hadd Robust
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Hadd Robust

what is the diff in case of dr/bdr?

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Waqas Karim
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Waqas Karim

There are 2 problems for OSPF on by multiaccess networks:
i. Multiple adjacencies
ii. Extensive LSA flooding

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Eaton Fox
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Eaton Fox

If OSPF is heavier on Router resources then how it uses less Bandwidth?
Why is OSPF heavier as compared to other protocols?

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Waqas Karim
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Waqas Karim

OSPF is resource intensive Protocol. The OSPF protocol is based on link-state or SPF technology. It uses Dijkstra’s algorithm to calculate the shortest paths between nodes which is a heavy protocol & requires a lot of mathematical calculations.

OSPF doesn’t need a lot of Bandwidth because it uses only triggered updates.

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