Unconfigured I-SID gets discovered by switch

[stefanhue]

Hi,

im a bit confused. I always thought that an isis member only discoveres members with the same i-sids that are configured on a switch. For e.g

Switch A: 1066,4042,5000

Switch B: 1066

Switch C: 5000

If i log in to switch B and do a "show isis spbm i-sid discover", I would think that I would only get "switch A" which also has i-sid 1066 configured, but for some reason the "discovery" returns 1066, 4024 and 5000 from "switch A" and i-sid 5000 from "switch C". This is really confusing. The i-sids i mentioned are just examples. "Switch B" also does not discover just every i-sid in our fabric and "switch B" is not the only one with this behavior. Also there are no FA devices connected to the switch. We are just doing basic c-vlans that are linked to i-sids in our fabric.

I hope i explained it in a way that is understandable ^^Thanks in advance !

[bar]

Hi stefanhue,

all your switches in your network in the same area need to discover and be aware of each other to learn a view of the network.  If you only want to see switches with the same i-sid configured try the command 

show isis spbm i-sid disc id 1066

[stefanhue]

Hi bar, 

thanks for the quick response :). So does the switch simply discover every i-sid in an area?, because that is not the case. It discovers all its locally configured i-sids and some random i-sids that aren't confiugured.

[bar]

Sorry stefanhue,

just re-read your question.  I think your understanding is correct.  I wouldn't expect switch B in your example to see switch C, nor i-sids 4042 or 5000 from switch A.

Sorry though, I can't come up with a reason that it would 😕