Prefix List still present after being deleted

[Brandon Matthee]

Good Day,

Problem Description: IP prefix lists are still being shown when using the “sh IP prefix” command despite being deleted and not in use by any route map

We have created new prefix list to replace old ones, however old prefix list still present after removing it. We created a test prefix and deleted successfully but the old prefix don't get removed. We don't see it in running config, but when doing the show command it still appears. see below example, Any advice? Do we need to do anything extra like reload or can it be ignored?

NA-CH3-CLD-RTR02#conf t  

Enter configuration commands, one per line.  End with CNTL/Z.  

NA-CH3-CLD-RTR02(config)#do sh ip prefix AZURE-SAN  

ip prefix-list AZURE-SAN: 0 entries  

NA-CH3-CLD-RTR02(config)#no ip prefix AZURE-SAN  

NA-CH3-CLD-RTR02(config)#do sh ip prefix AZURE-SAN  

ip prefix-list AZURE-SAN: 0 entries  

NA-CH3-CLD-RTR02(config)#end  

NA-CH3-CLD-RTR02#sh run | inc AZURE-SAN  

NA-CH3-CLD-RTR02#sh ip prefix AZURE-SAN  

ip prefix-list AZURE-SAN: 0 entries  

NA-CH3-CLD-RTR02#  

Product: Cisco ASR 1004 

Cisco IOS XE Software, Version 16.04.02  

Cisco IOS Software [Everest], ASR1000 Software (X86_64_LINUX_IOSD-UNIVERSALK9-M), Version 16.4.2, RELEASE SOFTWARE (fc1)  

Technical Support: http://www.cisco.com

[Georg Pauwen]

Hello,

what if you do a:

copy run start ?

[Richard Burts · Accepted solution]

The original poster asks "Do we need to do anything extra like reload or can it be ignored?" I believe that yes it can be ignored. And I believe that yes if you reload it will go away.

I am not authoritative on this but this is what I believe is happening: First we should acknowledge that while we tend to think of running config like it was a text file, that it is really a binary data structure. When you configured the prefix list it created an entry in the data structure. When you deleted the prefix list it removed the content of the prefix list. But the (empty) entry still exists and so it shows up in the output of show commands. A reload will re-initialize the data structure and the entry for that prefix list will no longer exist. I have seen similar behavior, for example, with Ethernet subinterfaces that were configured, were deleted, but still showed up in output of show ip interface brief till there was a reload.

[Brandon Matthee]

HI Rick,

Thank you very much for the detailed explanation. This answers the question

[Richard Burts]

You are welcome. I am glad that my explanation was helpful. Thank you for marking this question as solved. This will help other participants in the community to identify discussions which have helpful information. This community is an excellent place to ask questions and to learn about networking. I hope to see you continue to be active in the community.