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 …
Tag: 2b
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:
OSPF Type4 Message / LSU Packet (Link State Update)
Similar to LSR, LSU (Link State Update) is the response/reply to LSR. Each Link State Update packet carries a collection of link state advertisements one hop further from its origin. Consider the simple below topology with two Routers: LSU’s are generated in response to the LSR’s. It is obvious from the below detail, spend some time with it to understand it fully:
OSPF Type3 Message / LSR Packet (Link State Request)
LSR (Link State Request / Type3 OSPF Packets) is simply a request as obvious from its name. After DBD phase for first time, routers keep on sending LSR to keep the LSDB in sync. Consider the simple below topology with two Routers: After the Hello & DBD, Requests are made from Routers to query the missing Database Parts. It is obvious from the below detail, spend some time with it to understand it fully:
OSPF Type2 Message / DBD Packet (Database Descriptor)
DBD (Database Description or Type2 OSPF Packet) is a sort of summary of the OSPF Database in a router. DBD is used to check if the LSDB between 2 routers is the same. These packets are exchanged when an adjacency is being initialized. They describe the topology information a router has in its database. DBD uses poll-response procedure (master/slave). Master sends DBD packets/polls which are acknowledged by the slave. Consider the simple below topology with two Routers: As soon as we enable OSPF on the router interfaces, it starts exchanging Hello and DBD Packets. It is obvious Read More …