Tag: OSPF

OSPF Link STATE

Posted on by lechuck park

From DALL-E with some prompting
The image provides an overview of the OSPF Link State Advertisements (LSAs) and their contents:

The LSA Header includes general information about the LSA, such as its age, type, the router that generated it, and data integrity checks.

LSA Type 1 (Router LSA): This LSA type is used by routers to determine the best paths to other routers within the same area. It contains information about the router’s interfaces, connected routers (with Router ID), and the status and cost of each link.

LSA Type 2 (Network LSA): Generated by the Designated Router, it describes the routers attached to a multi-access network segment. It includes the network mask and a list of all routers on that network, facilitating the exchange of segment-specific router information.

LSA Type 3 (Summary LSA): Used by Area Border Routers (ABRs) to share internal network addresses between areas, summarizing the routing information and containing the network mask of the summarized routes along with the metric cost to reach them.

In essence, LSA Type 1 helps routers within the same area determine optimal routing paths. LSA Type 2 is used to exchange information about network segments and the routers connected to them. LSA Type 3 is for sharing summarized internal network addresses between different OSPF areas.

OSPF & BGP

Posted on by lechuck park

from DALL-E with some prompting
The image is an illustrative diagram explaining the interaction between two key protocols used in networking: OSPF (Open Shortest Path First) and BGP (Border Gateway Protocol).

  • In the center, we have a network labeled “AS (Autonomous System)” which is a collection of connected IP routing prefixes under the control of one or more network operators that presents a common, clearly defined routing policy to the internet.
  • Within the AS, the diagram shows a smaller network with purple lines connecting different nodes (routers), representing the OSPF protocol. OSPF is an interior gateway protocol used within an AS that distributes routing information between routers belonging to a single Autonomous System. The key features listed are:
    • “Sharing Link State (broadcast)” which means OSPF routers send link state advertisements to share the state of each directly connected link.
    • “with a Bandwidth” indicates that OSPF takes bandwidth into account when calculating the best route.
    • “Find Short Path (Dijkstra)” refers to OSPF using Dijkstra’s algorithm to find the shortest path through the network based on the cumulative cost of reaching each node.
  • On the right side of the diagram, there’s a larger network outlined in red, with blue lines connecting to a central node. This represents the BGP protocol, which is used between different ASes, especially at the borders. The features listed for BGP are:
    • “Border (of the AS) Gateway” which is the point where an AS connects to another AS.
    • “Sharing Routing Table between Border Gateways” means that BGP is responsible for exchanging routing information between autonomous systems, allowing them to see each other’s networks and determine the best paths.

The diagram uses solid lines to denote direct connections and dashed lines for indirect connections. The interplay between OSPF and BGP is critical for the overall functioning of the internet, with OSPF managing routes within an AS and BGP managing routes between ASes.

OSPF

Posted on by lechuck park

+ 224.0.0.6 (All Designated Routers) : Designated Router (DR) and Backup Designated Router (BDR). It is utilized to optimize communication between the DR and BDR, and regular OSPF routers do not receive messages from this address.

From DALL-E with Some prompting
The image is a visual representation of the operation of the OSPF (Open Shortest Path First) protocol. Here is the interpretation of each step depicted in the image:

get LS (Link State): OSPF routers collect cost values from all physically connected routers. This step involves determining the adjacency relationships between routers and the state of each link.

LSA (Link State Advertisement): Each router creates an LSA that contains its link-state information and disseminates it to other routers within the network. During this process, the multicast address 224.0.0.5 is used to broadcast the information to all OSPF routers.

LSDB (Link State Database): The information from the received LSAs is compiled into the LSDB of every OSPF router. This database should be identical across all routers within the Autonomous System (AS) and contains the complete topology information of the network.

Shortest Path Tree Calculation: Using the LSDB, each router calculates the shortest path tree from itself to all other destinations employing the Dijkstra algorithm. This calculation aids each router in determining the optimal routing paths.

Routing Table Update: The shortest path information calculated is then used to update the routing table of each router. This enables routers to forward packets using the optimal routes.

At the bottom, there’s a section titled Dynamic Updates, indicating that when there are changes in the network topology, new LSAs are generated and propagated through the network. This ensures that all routers’ LSDBs are updated and, as a result, the routing tables are also updated to reflect the new optimal routes.

In the top-right corner, it states “224.0.0.5 Broadcast IP for all OSPF router”, which indicates the multicast address used by all OSPF routers to receive LSA broadcasts.

This diagram provides a visual explanation of the core routing processes of OSPF, highlighting the mechanisms that enable efficient routing within the network and facilitate rapid convergence.


Overall IP Network

Posted on by lechuck park

From DALL-E with some prompting
The image is a diagram explaining the overall structure and data flow of an IP network.

Overall IP network: The entire structure of an IP network
Ethernet In the LAN: Ethernet used within the Local Area Network (LAN)
Identification in the internet: Identifying devices on the internet
OSPF short path with IP addresses: Open Shortest Path First (OSPF) routing protocol finds the shortest path using IP addresses
Addressing/Routing to the peer: Assigning addresses and routing to peer devices
BGP to get/share IP (other & me): Border Gateway Protocol (BGP) is used for obtaining and sharing IP addresses between others and oneself
Service Connection: Establishing a service connection
IP address ↔ Domain address: The relationship between IP addresses and domain addresses
DNS Easy to keep an internet address by Domain name: Domain Name System (DNS) makes it easy to maintain an internet address by using domain names
On TCP/UDP: Operating on TCP (Transmission Control Protocol) and UDP (User Datagram Protocol)
The diagram illustrates how data moves within a network. For instance, when a user accesses web services using the HTTP protocol, the DNS translates domain names into IP addresses, and then a service connection is established using the IP address over TCP/UDP protocols. Routing protocols such as OSPF and BGP are used to find the optimal path for data transmission through internal networks and the wider internet, respectively.