IS-IS and the loopback interface

[messy]

Hello all,

Just starting to get into my first networking job (have CCNA but no real experience). My company uses IS-IS and one of the first things I noticed was that someone seems to have tried to setup a loopback interface for management but its not working.

I have no intention of messing with anything config wise - I just have a question...from a quick read about IS-IS I understood that it didnt support virtual interfaces as it runs on layer 2 but then in IS-IS config guides I see them talking about setting up a loopback lo0

So....does IS-IS support virtual interfaces? If not then how does it support a loopback? Is a loopback not truly "virtual" in the sense that others are?

Thanks, 

[deanwebb]

https://www.juniper.net/documentation/en_US/junos/topics/task/configuration/isis-network-configuring.html#:~:text=The%20loopback%20interface%20(lo0)%20becomes,the%20loopback%20(lo0)%20interface.

"Every router in an IS-IS network must have at least one ISO NET address that identifies a point of connection to the IS-IS network. The NET address is generally configured on the loopback (lo0) interface. Routers that participate in multiple areas can have multiple NET addresses."

So it seems that multiple loopbacks would be needed for multiple area participation. But, yes, IS-IS does use virtual loopbacks, after a fashion.

[icecream-guy]

The benefit is that loopback interfaces never go down, oh, unless the router goes down as well.