OSPF
Open Shortest Path First (OSPF) is a link-state Interior Gateway Protocol (IGP) used to exchange routing information within a single autonomous system.
Explore different OSPF blog posts:
- OSPF Cheat Sheet
- OSPF Basic Config
- OSPF Summarization
- OSPF Overload
- OSPF Virtual Link
- OSPF Neighborship Requirements
- OSPF LSA
- OSPF Sham Link
Stay tuned for more.
OSPF Sham Link
1. Intro We will demonstrate the Sham Link usage with the following setup. We have CE1 and CE2 router that have a backdoor link between them. The main path between CE1 and CE2 should be via the MPLS L3VPN, so we configured a high metric between CE1 and CE2, as depicted in the next figure: […]
OSPF LSA
1. LSA Types OSPF uses different LSA types (Link State Advertisements) to share routing information between routers and build its LSDB (Link State Database). Each LSA type has a specific purpose and flooding scope where it is flooded only within or between areas. Find next more details about the LSA Types: 2. Wireshark First, let’s see the encapsulation of […]
OSPF Cheat Sheet
OSPF – Interior Gateway Protocol (IGP) Type: Link State Algorithm: Dijkstra Metric: Interface cost is auto-derived from bandwidth unless manually configured. Cost = reference-bandwidth / bandwidth Default reference-bandwidth = 100 000 000 (100 Mbps) External Metrics: Type 1: The sum of the internal costs plus the external cost. Type 2: Only the external cost assigned […]
OSPF Virtual Link
1. Intro For backbone areas only, create a virtual link to use in place of an actual physical link. All area border routers and other routing devices on the backbone must be contiguous. If this is not possible and there is a break in OSPF connectivity, use virtual links to create connectivity to the OSPF […]
OSPF Overload
1. Intro OSPF Overload: configure the local routing device so that it appears to be overloaded. You might do this when you want the routing device to participate in OSPF routing, but do not want it to be used for transit traffic. There is no overload bit, like we have in ISIS Overload. Instead, OSPF […]
OSPF Summarization
1. Intro In the previous post we applied OSPF basic config on our test network. We had 2 areas; one of them is a Totally NSSA area. In this post will do some OSPF route summarization on the same topology, continuing from where we left off. For easy reference find the OSPF database as it […]
OSPF Basic config
1. Intro In this post we will apply OSPF basic config on our test network. We have 2 areas; one of them will be a Totally NSSA area. In the next post will do some OSPF route summarization on the same topology. 2. OSPF Basic config We will configure a topology with multiple areas: The […]
OSPF Neighborship Requirements and Troubleshooting
1. Intro It is often times a struggle to bring up an OSPF Neighborship between two routers. Well, it can be if you don’t clearly know all requirements. In this post we will see all OSPF neighborship requirements and how to troubleshoot when the neighbors are not UP. As a network engineer we must know […]