what cause the isis hostname display a wrong System ID (not loopback addr)?

[Ma Juner]

hi all experts,

     I have a long time confusion on the isis nametable list.

     When I show isis hostname, some router node will display the right hostname but a wrong System ID,

     a odd ip address that never broadcasted in my network.

     In fact, all the loopback interface have been joined in the isis protocol.

     Please tell me the reason why this mismatch happened? And if there is some good method to resolve this

    problem when we cannot break off the isis connection and cannot affect the business?

    Thx all

[Peter Paluch]

Hello,

I am not sure if loopbacks have anything to do with the SystemID. The SystemID is a part of the net command used inside the "router isis" configuration. If it corresponds to a loopback, it is only because the administrator has manually configured the net command to resemble the loopback's address. There is no automatic conversion of loopback address to SystemID implemented in Cisco's IS-IS implementation.

Would it be possible to post the following?

1. show isis hostname from a router that displays the allegedly wrong hostname/SystemID combination
2. The configuration of the IS-IS on the corresponding router with that hostname/SystemID

Thank you!

Best regards,

Peter

[Ma Juner]

hi Peter,

   I configured the ISIS net in the right format (the NET format using the loopback's address),

   but I can't get the hostname with its legal SystemID.  

   a simple example:

router isis 100

net 46.0100.0110.2200.0113.00
is-type level-2-only

interface loopback

ip address 11.22.0.113

show isis hostname

Level  System ID      Dynamic Hostname  (100)

2     0071.125.3081   XXX-7609

   I want to know what's cause that phenomenon.. And how can I get the legal display.