Cisco CCNP/ BSCI Tutorial: Contrasting OSPF and ISIS
Cisco CCNP/ BSCI Tutorial: Comparing OSPF and ISIS Hellos
While studying to pass the BSCI test and preparing to make your CCNP accreditation, you'll rapidly observe that while OSPF and ISIS are both link-state procedures, there are a great deal of distinctions between the two. One significant difference is the means the two procedures manage hi packets.
Hello packages are crucial to keeping OSPF and ISIS adjacencies alive. Given that they are both link-state protocols, neither of them will certainly send updates at any type of specified time. Hey there packets are the only approach through which routers running OSPF and ISIS can see that a surrounding router is still available.
OSPF gives us some fantastic alternatives when it pertains to maintaining transmitting table dimension down using using stub and total stub areas, but to OSPF, a hey there packet is a hello there packet. ISIS routers can sending out 2 different sorts of hellos-- Degree 1 and Level 2.
ISIS routers are classified as Level 1 (L1), Degree 2 (L2), and Degree 1-2 (L1-L2). By default, Cisco routers are L1-L2 routers; this means that every ISIS-enabled user interface will certainly send both L1 and L2 hellos.
If among the user interfaces is developing just an L1 or L2 adjacency, there's no factor to send hellos for the other adjacency type. For instance, if R1 is creating an L1 adjacency with R2 by means of its ethernet0 interface, there is no reason to enable the router to transmit L2 hellos. To hardcode a router interface to send out only L1 or L2 hellos, utilize the isis circuit-type command.
R1(config)#interface ethernet0
Keep in mind: To configure this interface to send out only L2 hellos, the complete command is "isis circuit-type level-2-only", not just "level-2".
This Dan Herbatschek arrangement would certainly avoid L2 hellos from being sent out ethernet0. While this does save router sources and avoids unneeded bandwidth usage, there is also no way an L2 adjacency can be formed-- Dan herbatschek information so double-check your network geography before utilizing this command!