Virtual Link is a non-Physical connectivity or link. As we know OPSF must be connected with Backbone Area0 but sometime it becomes difficult due to some reasons. So there we required Virtual Links for logical connection to Backbone. Also known as logical link which uses in least cost path connectivity between routers or ABR or backbone/Non-backbone. A virtual link does not have ABR physical Connectivity to Backbone till to configure virtual link between non-backbone area and Backbone. In between two routers, a virtual link can be configured, that have an interface to a single common Transit/Non-backbone area but it can’t Read More …
Category: Layer3
OSPF Authentication
What is Authentication: Authentication is the mechanism of recognizing the identity of a user. Associating an incoming request with a set of identifying credentials is called Authentication. The credentials provided are compared to those in the database of the authorized user’s information register on a local operating system or somewhere remote. If the user is on white-list then he/she is allowed the access, otherwise the access is rejected simply. Types of OSPF Authentication OSPF supports two types of authentication i.e. Plain Text authentication and Message Digest 5 (MD5) authentication. As a message/packet required authentication for both destinations. Read More …
Yet another difference b/w IS-IS and OSPF
Neighbour is someone who lives nearby, normally in a house or apartment that is next door or, in the case of houses, across the street. Some neighbors are adjacent while some are not. People form friendships with their neighbors, and help them by sharing their information & tasks. Similarly, in Network & routing world there is a difference in neighborship & adjacency. OSPF neighbourship is straightforward while IS-IS needs a bit deeper thought to get it fully. Lets take a closer look at both. For OSPF, in order to form OSPF adjacencies, the following must match on the neighboring routers: Read More …
A brief flashback of IS-IS – Part I
IS-IS is categorised under Link State type of protocols & it is based on Dijkstra Algorithm same as OSPF. Admin Distance defaults to 115 & metric is 10 for all type of links (contrast to OSPF which has different cost for different type of media). It was originally standardized by ISO in 1987 (ISO10589) which was later adopted for TCP/IP type of networks & was called as Integrated IS-IS under RFC1195 (1990). Integrated/Dual IS-IS supports IP Routing while original IS-IS only supported CLNP routing. It supports both ISO’s Connectionless-Mode Network Service (CLNS) and IP. IS-IS runs on Layer2 in contrast to OSPF which Read More …
OSPF Type5 Message / LSAck Packet (Link State Acknowledgment)
Finally, Acknowledgements are needed once the LSR/LSU (request/reply) process is complete. Type5 OSPF Packets are used for this purpose which are called LSAck (Link State Acknowledgment). Consider the simple below topology with two Routers: After LSU’s, LSAck’s are sent as a confirmation message. It is obvious from the below detail, spend some time with it to understand it fully: