IS-IS Router Classification and Area

Latest reply: Dec 26, 2018 07:30:39 201 7 8 0

In IS-IS, routers are classified into the following types: Level -1, Level-2, or Level-1-2

Level-1: A Level-1 router is an internal router in an IS-IS area. A Level-1 router can establish neighbor relationships only with other Level-1 routers in the same area or Level-1-2 routers in the same area. The Level-1 router maintains only the Level-1 LSDB. It calculates the network topology in the area and the optimal route to each network segment in the area according to the link state information contained in the LSDB. Level-1 routers must be connected to the IS-IS backbone network through Level-1-2 routers to access other areas.

Level-2: A Level-2 router can be considered as a backbone area router. It can establish IS-IS neighbor relationships only with Level-1-2 or Level-2 routers. A Level-2 router maintains only Level-2 LSDBs.

Level-1-2: The router can establish a neighbor relationship with a Level-1 router or establish a neighbor relationship with a Level-2 router. The role of the router is similar to that of an ABR in OSPF. It is usually connected to a Level-1 area and a backbone area. The Level-1 LSDB and Level-2 LSDB can be maintained at the same time. As a bridge between Level-1 areas and other areas, the Level-1 area delivers the Level-1 LSP and sets the ATT bit in the LSP to notify the Level-1 routers in the area to reach the external area of the area, the intra-area router generates a default route pointing to the Level-1-2 router according to the LSP with the ATT bit set.

Hierarchical IS-IS design: Backbone area and non-backbone area
A backbone area is a series of consecutive Level-2 and Level-1-2 routers. It is not unique.
A non-backbone area is a Level-1 area that consists of consecutive Level-1 routers (including Level-1-2 routers) and is also called a non-backbone area.

In the IS-IS network area design, the Level-1 area must be directly connected to the backbone area through a Level-1-2 router. The Level-1 area can be regarded as the Totally Stub area. By default, the Level-1-2 router does not learn the routes learned from the backbone area, routers in other areas advertise routes to the local Level-1 area.

  • x
  • convention:

Created Dec 25, 2018 03:47:32 Helpful(0) Helpful(0)

Hierarchical IS-IS design: Backbone area and non-backbone area.Can you provide a more detailed explanation?
  • x
  • convention:

Created Dec 25, 2018 06:15:35 Helpful(0) Helpful(0)

The role of the router is similar to that of an ABR in OSPF. It is usually connected to a Level-1 area and a backbone area. this is very helpful guide on IS-IS Router Classification and Area
  • x
  • convention:

Created Dec 25, 2018 06:46:56 Helpful(0) Helpful(0)

IS-IS is more scalable than OSPF
  • x
  • convention:

Created Dec 25, 2018 08:40:43 Helpful(0) Helpful(0)

Finally, solved my puzzle on this level term. This explanation is very detailed.
  • x
  • convention:

Created Dec 25, 2018 10:04:33 Helpful(0) Helpful(0)

IS-IS have three type, Level 1, Level 2, Level-1-2, if the device is on the backbone, we suggest to set it on the Level 2
  • x
  • convention:

MVE Created Dec 25, 2018 13:53:13 Helpful(0) Helpful(0)

ospf is better used
  • x
  • convention:

MVE Created Dec 26, 2018 07:30:39 Helpful(0) Helpful(0)

well explained
  • x
  • convention:



You need to log in to reply to the post Login | Register

Notice Notice: To protect the legitimate rights and interests of you, the community, and third parties, do not release content that may bring legal risks to all parties, including but are not limited to the following:
  • Politically sensitive content
  • Content concerning pornography, gambling, and drug abuse
  • Content that may disclose or infringe upon others ' commercial secrets, intellectual properties, including trade marks, copyrights, and patents, and personal privacy
Do not share your account and password with others. All operations performed using your account will be regarded as your own actions and all consequences arising therefrom will be borne by you. For details, see " Privacy."
If the attachment button is not available, update the Adobe Flash Player to the latest version!
Login and enjoy all the member benefits

Login and enjoy all the member benefits