[Series of OSPF] Episode 7 a summary of OSPF, introduce something overlooked easily by using OSPF Highlighted

Latest reply: Dec 23, 2018 14:34:30 471 20 2 1

In the previous 6 episodes, we talked about the OSPF from a lot of ways. In this episode, we will make a summary of OSPF, talk about something overlooked easily in OSPF.

  1.  About MTU mismatch at both ends of a link. As we know, there is MTU inspection mechanism in OSPF, it requires MTU at both ends of a link should equal to each other, or no adjacency relationship could be established. This inspection mechanism is disabled by default on Huawei devices, this will lead two devices can establish adjacency relationship when they connect to each with mismatch MTU. If we enable MTU inspection on the interface view, this will make OSPF relationship stuck in exstart. Though when disable the inspection mechanism OSPF can establish full adjacency relationship, it's strongly recommanded not to do that.
  2. In a multi-access, DRother router will send LSU to the 224.0.0.6, then DR send LSU to 224.0.0.5 to notice other DRother router.
  3. In a NBMA network, we should assign a OSPF neighbor manually. 
  4. a simple solution to speed up the convergence is adjust the hello interval down. 
  5. when adjust the hello interval manually, the dead interval will adjust itself automatically, on the contrary, when adjust the dead interval, the hello interval wouldn't adjust itself. 
  6. when two routers configured with the same router-id, they wouldn't establish neighbor relationship, 
  7. when an interface is configured as silent-interface, it wouldn't send ospf hello packets out, so it can't establish neighbor relationship with the remote device. But it doesn's mean the network segment the silent-interface belongs to wouldn't be advertised by other interface in the same area, on the contrary, this network segment will be advertised by other interface in the same area. 
  8. In OSPF, multi-area and multi-process are quite different from each other. multi-area indicates multi areas on the router, commonly, they belong to a same OSPF process, LSAs can be exchanged between different areas. Multi-process indicates multi processes are enabled on the router, they are independent from each other, working as two routing protocols, so they cann't exchange routes by default, unless import route from each other. 
  9. DR, BDR, DRother and ABR, ASBR are two ways to distinguish the router. The first way indicates the roles during exchanging LSAs, the second way indicates the roles based on the different areas. 
  10. router will advertise type 3 net-summary LSA default route to the stub, totally stub and totally NSSA area, on the other hand, router will advertise NSSA default route to the NSSA area. 
  11. the OSPF packets are encapsulated with TTL equals to 1. 
  12. The election of DR and BDR are taken place during the 2-way state. 
  13. Attempt state is only valid for manually configured neighbors in an NBMA environment. 
  14. DR and BDR cann't be preempt.

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Created Dec 15, 2018 23:07:03 Helpful(0) Helpful(0)

Thanks you
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Created Dec 15, 2018 23:17:51 Helpful(0) Helpful(0)

Good
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Created Dec 15, 2018 23:30:29 Helpful(0) Helpful(0)

Good
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Created Dec 15, 2018 23:32:11 Helpful(0) Helpful(0)

Thanks you
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Created Dec 18, 2018 11:15:49 Helpful(0) Helpful(0)

could you please introduce the tech with the specify examples or topologies
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Created Dec 18, 2018 15:16:44 Helpful(0) Helpful(0)

Open Shortest Path First (OSPF) is a routing protocol for Internet Protocol (IP) networks. It uses a link state routing (LSR) algorithm and falls into the group of interior gateway protocols (IGPs), operating within a single autonomous system (AS). It is defined as OSPF Version 2 in RFC 2328 (1998) for IPv4.[1] The updates for IPv6 are specified as OSPF Version 3 in RFC 5340 (2008).[2] OSPF supports the Classless Inter-Domain Routing (CIDR) addressing model.
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Created Dec 18, 2018 17:34:05 Helpful(0) Helpful(0)

Need more tools
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Created Dec 19, 2018 20:32:10 Helpful(0) Helpful(0)

Thanks for sharing
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Created Dec 22, 2018 09:14:01 Helpful(0) Helpful(0)

DR, BDR, DRother and ABR, ASBR are two ways to distinguish the router. The first way indicates the roles during exchanging LSAs, the second way indicates the roles based on the different areas.

learned a lot. thank you!
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Created Dec 22, 2018 16:32:27 Helpful(0) Helpful(0)

Good
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