Hello packet, also called Type1 OSPF Packet, is a special packet/message that is sent out periodically from a router to establish and confirm network adjacency relationships. These packets are sent periodically on all interfaces in order to establish and maintain neighbor relationships. Hello Packets contain different parameters including Network mask, Hello Interval and Router Dead Interval,…. These parameters are needed to form neighbor relationships. All routers connected to a common network (NBMA,…) must agree on certain parameters. Below is the detailed description of Hello Packet & its fields: Below is description of fields in the OSPF Hello Packet: Read More …
Tag: Link State Routing Protocols
OSPF Packet Formats
There are different OSPF Packet Types which are used for different purposes. OSPF has five types of Packets. OSPF uses its own protocol and doesn’t use a transport protocol like TCP or UDP. It uses IP Protocol 89. Let us have a detailed look into each type of Packet now. Below is a general view of OSPF Packet. When changing from one type to another in above five categories, just the TYPE & DATA fields are changed. This is how it will look when we deep dive into the packet itself. Below are the five types of Packets in detail Read More …
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 Read More …
Hello Protocol
“A protocol used by Layer3 devices (like Routers) to discover neighbors and form adjacencies with each other” When a protocol process starts on a router, neighbors must be discovered and adjacencies must be established. Hello is a protocol which performs this duty. Hello protocol performs several functions, including but not limited to: It discovers neighbors (such as OSPF or IS-IS routers) It performs three-way handshaking to ensure bidirectional communication between the neighbors. It communicates information necessary for establishing whether an adjacency can be formed with a neighboring router After an adjacency is formed, it serves as a keepalive mechanism to Read More …
OSPF Timers (OSPF Intervals)
Routing protocol use Timers (Intervals) to keep all routers in a domain updated. Through the use of these timers, a routing protocol is able to maintain a stable neighbor relationship and ensure routes are propagated correctly. OSPF routing devices constantly track the status of their neighbors by sending and receiving Hello Packets to confirm whether each neighbor still is functioning normally. We can use these OSPF Intervals (OSPF Timers) to adjust the network convergence time in an OSPF network. Types of OSPF Timers: OSPF uses two types of OSPF Intervals (Timers): Tells the router after how long should it Read More …