Cisco – Why does a Cisco AP keep its static IP when erasing NVRAM

ciscowireless

When I erase the nvram on a Cisco AP (1252 and 1262), the static IP assigned to interface BVI1 is not erased. When I do a show startup-config it says there is no startup config. But it always boots with that IP until I manually set it to DHCP assigned. Then when I reboot (without saving) it comes up as DHCP.

If I erase it using the reset button on power up, the IP does not stick.

I can only imagine this is intended to keep from losing access to the AP when you erase the config. If this is the case, is there a command to wipe the IP too?

Extra details:

IOS: 15
Autonomous

Best Answer

You are correct, they leave the IP information so that you don't accidentally lose connectivity when working on an AP remotely. As you noted, the button (which requires you to be local) will default the configuration including the IP.

You can also do this by entering the following command:

write default-config

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Cisco IOS SNMP – When Does the ifCounterDiscontinuityTime Counter Change?

The ifCounterDiscontinuityTime is triggered when interfaces are dynamically removed from a device and then that same interface is dynamically re-added. I tested this using a loopback interface but I believe the behavior would be the same for modular interface whose existence would change based on whether or not the module was present. The steps to reproduce this are below and there is some further reading on this topic in the RFC here: https://www.rfc-editor.org/rfc/rfc2863#section-3.1.5

1. Create loopback 100 and find it's ifindex

router1#conf t
router1(config)#int loopback100
router1(config-if)#end

[user@host logs]$ snmpwalk -v 2c -c $COMMUNITY router1 .1.3.6.1.2.1.2.2.1.2 | grep Loopback
IF-MIB::ifDescr.67 = STRING: Loopback100

2. Check the current value of ifCounterDiscontinuityTime for Loopback100

[user@host logs]$ snmpwalk -v 2c -c $COMMUNITY router1 1.3.6.1.2.1.31.1.1.1.19.67
IF-MIB::ifCounterDiscontinuityTime.67 = Timeticks: (0) 0:00:00.00

3. Remove Loopback100 and check the value of ifCounterDiscontinuityTime

router1(config)#no int loopback 100

[user@host logs]$ snmpwalk -v 2c -c $COMMUNITY router1 1.3.6.1.2.1.31.1.1.1.19.67
IF-MIB::ifCounterDiscontinuityTime.67 = No Such Instance currently exists at this OID

4. Re-add Loopback100 and check the value of ifCounterDiscontinuityTime

router1(config)#int loopback 100

[user@host logs]$ snmpwalk -v 2c -c $COMMUNITY router1 1.3.6.1.2.1.31.1.1.1.19.67
IF-MIB::ifCounterDiscontinuityTime.67 = Timeticks: (111308186) 12 days, 21:11:21.86

Cisco Routers – Why Boot-Sequence is Stored in NVRAM by Default

The flash is where the IOS image is stored in a compressed file (.bin). The NVRAM is the uncompressed file from Flash.

Changing the configuration register is sometimes needed in the case of the password recovery process. It can also be used for:

How the router boots (into ROMmon, NetBoot)
Options while booting (ignore configuration, disable boot messages)
Console speed (baud rate for a terminal emulation session)

Cisco's complete guide to config register commands/use on ALL routers: https://www.cisco.com/c/en/us/support/docs/routers/10000-series-routers/50421-config-register-use.html

Personally i've only made use of changing the config register in practice a few times, mostly password recovery on the old Cisco 2600 and 2800 Series Routers.

Once i had to fiddle about with the baud rate in order to send a file faster to a router via console.

Best Answer

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Cisco IOS SNMP – When Does the ifCounterDiscontinuityTime Counter Change?

Cisco Routers – Why Boot-Sequence is Stored in NVRAM by Default

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