RANCID and IOS 15.2 – blank config and how to work around newer file privileges

In or around IOS 15.2 apparently a privilege structural change was made that breaks non-priv-15 users from being able to copy the running config, useful for RANCID and other tools.  And either the RANCID/Oxidized community simply uses privilege 15 users in their configs, which I refuse to do on priciple, or my google-fu is poor because I have not found this info in any explicit form.

In any case, the symptom of the typical config allowing to download a running config without having level-15 privileges on Cisco IOS has always been documented as:

username rancidbackup privilege 10 secret [md5-pass]
privilege exec level 10 show running-config view full
privilege exec level 10 show running-config view
privilege exec level 10 show running-config
privilege exec all level 1 show

 

the above in IOS <= 15.1 was always enough to allow user “rancidbackup” to issue a “show running-config view full” and the CLI would output the current configuration.  Under IOS 15.2, behaviour appears to have changed.  Some folks receive a “permission denied” error while others, such as my experience, a simple empty config would be output.  As an example:

ssh -l rancidbackup 10.0.255.1

Password: 

Router#show running-config view full
[...nothing...]
Router#show running-config
[...nothing...]          
Router#

This annoying behaviour can be worked around in two different ways.

The first, is to cave and allow the rancid backup user to obtain level-15 privileges upon login.  The academic risk of compromise by this admin-level user can be mitigated by limiting the IP addresses used for login via ACL:  example:

username rancidbackup access-class 99 privilege 15 secret [md5-pass]
!
access-list 99 remark RANCID-ONLY
access-list 99 permit host 10.0.1.25 any
!

By adding access-class to the username definition, it is possible to avoid this user being used from other sources.  This might even be recommendable for any scenario where scripting/tools are used for access to the device.  However, this method still requires that user to have admin level-15 privileges.

 

I was pointed to https://supportforums.cisco.com/discussion/11691446/error-opening-nvramstartup-config-permission-denied as a possible second solution.  Apparently there is a mecanism to allow file access (which includes running-config, apparently…), with the command “file privilege [level]”

In our case, by issuing “file privilege 10”, we are able to see via “show running-config view full” (and not just show running-config) the info we seek to backup with our tool, in this case RANCID (as you can see, “show running config” is useless but “show running-config view full” outputs what we need):

 

Router#show running-config 

Building configuration...
Current configuration : 261 bytes
!
! Last configuration change at 22:04:36 EDT Mon May 30 2016 by user
! NVRAM config last updated at 13:15:46 EDT Thu May 26 2016 by user
! NVRAM config last updated at 13:15:46 EDT Thu May 26 2016 by user
boot-start-marker
boot-end-marker
!
!
!
!
!
!
!
end

Router#show running-config view full 
Building configuration...
Current configuration : 90474 bytes
!
! Last configuration change at 22:04:36 EDT Mon May 30 2016 by user
! NVRAM config last updated at 13:15:46 EDT Thu May 26 2016 by user
! NVRAM config last updated at 13:15:46 EDT Thu May 26 2016 by user
upgrade fpd auto
version 15.2
.... etc etc
!

huzzah!

I am still researching secondary implications from setting “file privilege” to anything other than level-15.  I haven’t found a way, using a privilege 10 user, to modify/delete the files so use at your own risk (!).  But combining the two above mecanisms I believe provides a sufficient means to allow non-privileged, read-only access to the configuration for use with config management and other scripting tools.

 

Cisco IPv6 flow export with “Flexible Netflow”

Sometime between IOS 12.4 and 15.x, IPv6 flow export configuration changed.  It used to be quite simple:

Pre-flexible-netflow configuration:


voilà….IPv4 and IPv6 flows exported to your favorite collector (mine being the wonderful and always useful  NFDUMP/NFSEN).

Somebody at Cisco obviously found this too easy, so it is now required to re-engineer this functionality into “Flexible Netflow”.  It does allow you, via the creation of a flow record, customize your own format, which is beyond this simple blog post and likely my current understanding as well ;).

For my purposes, I simply want to export IPv6 flows to my collector for business as usual.  This is done by defining a flow exporter and flow monitor, attaching the exporter to the monitor, in the gobal configuration, and applying it to the interface somewhat as before:

Flexible-netflow configuration:


Presto. The original-output defined in the flow monitor specifies using the predefined (?legacy?) record instead of specifying a flow record with user-defined parameters.

And as a side note, if you haven’t played with NFDUMP/NFSEN, you really should give it a try, its very useful as a tool for traffic analysis/DDoS/post-mortems.