There are different OSPF Packet Types which are used for different purposes. We know that OSPF routers need to perform different duties in order to route traffic. e.g. establish and maintain adjacencies, send and receive requests, ensure reliable delivery of Link State advertisements (LSAs) between neighbors and to describe Link State Databases. All these duties are performed using messages/Packets. Only one type of message/packet cannot perform all these duties. So, different types of messages/Packets are needed. OSPF has five types of Packets in total which are listed in below. Each type of packet has its own duties to perform. All these Read More …
Tag: OSPF
Network statements in Lazy mode & Deep dive into OSPF Network command
During my journey of CCIE, I noticed an OSPF feature worth of sharing. In Core/IGP routing, instead of typing a lot in network commands in OSPF, we can just use network 0.0.0.0 255.255.255.255 and more surprisingly 0.0.0.0 0.0.0.0. Once you enter all zeroes, running-config will convert it to quad 0 followed by quad 255. We can also use 0.0.0.0 0.0.0.0. It just includes all interfaces the same way as if you do 0.0.0.0 255.255.255.255. Below is the practical demonstration: If the router has all interfaces in a single area, I always use network 0.0.0.0 255.255.255.255 area area-id. Since, 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 …