Let's say I have three routers : R1, R2, and R3.
R1 is connected to R2, and R2 is connected to R3, so R2 is the router sitting in the middle and interconnecting R1 and R3.
R1 IP Loopback address : 22.214.171.124
R2 IP Loopback address : 126.96.36.199
R3 IP Loopback address : 188.8.131.52
Which command can I use on Router R1, to verify inside the ISIS database, that R2 (specifically) is advertising the loopback of R3.
I know if I check the routing table I will see it, but I want to check that information inside the ISIS database. Also I do not want to check the whole ISIS database but only the part of the database which is related to R2.
ISIS is not RIP and not BGP, so R2 won't be "advertising" prefix that belongs/exists on R3, unless You get really creative with non-forwarding instances and such.
In typical design, R3 will be "advertising" the subnets that belong to it. Ditto for R2 and R1.
And in Your case, R2 will be only propagating/flooding the ISIS LSP PDU that R3 originated and flooded.
As for checking part of ISIS database, this command is advised
Specifically, in Your case
show isis database extensive BLAH | no-more
- where BLAH is the system-id or hostname of the originating router in question.
You can check mapping of ISIS system-ids to hostnames with
show isis hostname | no-more