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A quick difference: OSPF Vs IS-IS Dynamic Routing Protocol

August 24, 2020 ,

 Today I am going to talk about the difference between the two different Dynamic routing protocol. These protocols are widely used in the enterprise networks and is one of the most important topic which I am going to cover now.


I will create Table showing the feature and the difference of these features in OSPF and IS-IS routing protocols.Both OSPF and IS-IS are Dynamic Routing protocol and works on the Link State routing protocol technique

Fig 1.1- OSPF vs ISIS routing protocol design


OSPF
OSPF is the most widely used routing protocol in large enterprise networks. OSPF is based on link-state technology by using shortest path first(SPF) algorithm which calculates the shortest path among all the possible path. 

OSPF puts the possible route in the topology map and select the best route to travel which will be the shortest path among all the possible route.

IS-IS Routing Protocol
Intermediate System to Intermediate System intra-domain routing protocol is a Link State Protocol and is a dynamic routing protocol based on SPF routing algorithm. It is an IGP (Interior Gateway Protocol) scalable only for dynamic routing within a domain and supports a 2-level hierarchy : level-1 (areas) and level-2 (backbone).

Integrated IS-IS, also known as Dual IS-IS, was to provide a single routing protocol with the capabilities of routing both Connection-less Network Service (CLNS) and IP

IS-IS routing Logic
L1 router: for a destination address, compare the area ID to this area. If not equal, pass to nearest L1/L2 router and If equal, use L1 database to route by system ID
L1/L2 router: for a destination address, compare the area ID to this area. if not equal, use L2 database to route by area ID and If equal, use L1 database to route by system ID.


Just to take the basic difference as :
  • OSPF needs 2 process if you want to run IPv4 and IPV6 whereas ISIS need can be configured with 1 process only. The TLV are a big benefits for ISIS.
  • ISIS can implement the authentication between the areas and OSPF cannot. Also ISIS can ignore the TLV that doesn’t understand in order to make the extendability and compatibility easier, OSPF cannot ignore the LSAs.
  • OSPFv3 can run IPv6 and IPv4 in a single process.

    Difference between OSPF and ISIS routing protocol below


Click on the above mentioned image to get the clear view of the difference between OSPF and IS-IS routing protocols.