Hello everyone,
Today I will share with you the differences between IS-IS and OSPF.
IS-IS supports only point-to-point and broadcast subnets. OSPF supports P2P, broadcast, P2MP, and NBMA networks.
OSPF areas are divided based on interfaces. IS-IS is divided into areas based on route routes.
The conditions for establishing an adjacency are different.
The Hello protocol used by IS-IS is simple and OSPF is complex. In addition, the IS-IS check is loose, and the Hello time and Dead time between the master and slave devices do not need to be the same, but the OSPF requirements are the same.
The OSPF adjacency on a point-to-point link is more reliable than that on an IS-IS network.
IS-IS uses the two-way handshake mechanism to form an adjacency relationship. However, there are three handshake mechanisms.
In OSPF, different DRs on a common router form an adjacency relationship. IS-IS adjacencies are established.
The DR and DIS election processes are different.
The DIS election of IS-IS is simple and predictable. The DIS with the highest priority is the DIS, and the DIS with the priority of 0 may also be the DIS.
To ensure a small change, OSPF DR election is complex and unpredictable. The DR with the highest priority is not necessarily the DR. The DR with the priority of 0 cannot become the DR. The DR fails, the BDR immediately takes the responsibility of the DR. The IS-IS does not back up the DIS. As a result, the DIS fails and the DIS is re-elected.
There are many types of OSPF LSAs and the database structure is complex. Therefore, it is difficult to locate faults. IS-IS LSPs include only router LSPs and pseudonode LSPs. The database structure is simple and faults can be located easily.
The synchronization process is different.
The OSPF LSA lifetime is increased from 0 (0~ 60 minutes, and the period cannot be configured). IS-IS decreased from the maximum value (20 minutes ~0, configurable period)
OSPF uses the prefix as the SPT node. IS-IS uses the prefix as a leaf.
The SPF algorithm of ISSI is simple. In addition, IS-IS uses the prefix as the SPT leaf. Therefore, when the leaf changes, you can use partial route calculation (PRC) to update the leaf without performing the SPF calculation.
That is all I want to share with you! Thank you!
