Introduction to IS-IS

[anoopst1993 (Anoop T)]

Mostly ISIS is used in SP and OSPF is used in enterprise networks
Wherever i read there is a statement made that ISIS is more scalable than OSPF
Can u explain how is ISIS more scalable than ospf with a real scenario
Thanks

[lagapidis (Lazarus Agapidis)]

Hello Anoop

Take a look at this post:

OSPF Path Selection explained

Hello Swapnil Both IS-IS and OSPF are link state protocols, and both use the same Dijkstra algorithm to compute the best path through the network. However, they do have a few differences in their architecture. You can read more about the differences here: Specifically concerning scalability, IS-IS does not use as much bandwidth to function as OSPF and its algorithm is less CPU and memory intensive. As stated in the above link, “Given the same set of resources, IS-IS can support more rou…

I hope this has been helpful!

Laz

[richardurassa411 (Richard Urassa)]

Hey Laz,
Can i have some inputs regarding UP/DOWN bit in ISIS in comparison with ATT bit.

[lagapidis (Lazarus Agapidis)]

Hello Richard

For information about the up/down bit, take a look at the following lesson:

IS-IS Route Leaking

For information bout the attached bit (ATT) take a look at this lesson:

Introduction to IS-IS

In summary:

• Once a level 1-2 router is connected to another area, it will set the ATT bit in its level 1 LSP. When a level 1 router sees this, it will generate a default route that is pointed to the level 1-2 router.
• The up/down bit is used to indicate to an L1-L2 router not to redistribute a network that has already been redistributed. This is a loop prevention mechanism.

I hope this has been helpful!

Laz