reload - interesting observation

[bs_kwaj]

Today I had a lab all set up and then saved all of the configurations to my tftp server. The plan is to erase everything and then restore it all from the tftp server and verify I can still ping from one end of the network to the other.

I went to each router and switch and ran 'erase start' or 'erase startup-config'. (...depending on the device.)

At each device, after running the erase command, I ran 'reload'. As expected, that eliminated all of the configurations; the passwords, the RIP settings, the FastEthernet settings, etc.

All except:

I have an 1841 with a WIC-2T. One connection is to a 2651XM with a WIC-1T and the other is to a 3640 with an NM-4T card. After the 'reload', the connection to the 3640 retained its IP address. The connection to the 2651XM was reset and showed 'no ip address'.

Ater running 'erase startup-config' and then running 'reload' on the 3640, the 2 serial ports that were configured on the NM-4T card retained their IP addresses as well.

I thought 'reload' should wipe those out. ??

[bs_kwaj]

Apparently, serial connections are very robust. ;)

I ran reload on the 3640 again and the serial ports remained configured. So, I disconnected the serial cables and ran reload again and this time the serial ports went back to a 'no ip address' state.

After that, I ran reload on the 1841 and this time its serial interface also went back to 'no ip address'.

On the 3640 I didn't disconnect the Fa0/0 port from the tftp server, but the erase and reload did wipe out that IP address and I didn't have to disconnect it.

So, moral of the story, if you want to 'reload' a device, disconnect the serial cables first.

[lammle]

Cisco has this WONDERFUL proprietary protocol that came out in 1991 I beleive, called SLARP.
It was created before most people could spell TCP/IP for someone that connected a serial link and could only configure one interface - barely.
if it detects CD, it automatically figures out what the remote IP is and assigns itself the next IP in the range. nice, huh?
show ip int brief will show you that it was assigned via slarp.
Welcome to Cisco's wonderful world of features...
Todd

[Big Evil]

Yeah i saw this once, thanks TL for the information there.

[bs_kwaj]

I hadn't realized that the IP address may have changed. So, just for fun, I restored the 1841 and 3640 from the tftp server. I changed the IP addresses to 172.16.11.7 on the 1841 and to 172.16.11.14 on the 3640.

Then I erased the startup-config on the 1841 and ran reload. Sure enough, there it was, the IP address was now 172.16.11.15.

IOS is fun!
;)

[Big Evil]

Yeah you have to love the IOS for weird stuff.

With BGP under the AS if you have a statement BGP to redistribue something, you remove the line under the AS with no - do a sh run | s bgp [AS] the network you want to stop is gone but the redistrbute string is still there! Nice.

The other week two switches in a rack of six (all 2960 48 port POE), decided to stop trunking to the switch above and the one below.
I added the line switchport mode trunk, and hey presto they came up.
The only had on there switchport trunk encap qot1q, like the rest. But after having an up time of two years decided the need the other cmd also. Thankfully i never set these up in the first place.