[c-nsp] Mass-renaming interfaces

[Eugene Grosbein]

28.09.2020 17:12, James Bensley wrote:

> On Mon, 28 Sep 2020 at 07:35, Eugene Grosbein <eugen at grosbein.net> wrote:
>> One of my 7201 routers has four GigabitEthernet interfaces but uses only two,
>> one for IP uplink and another as client-sided downlink with multiple
>> sub-interfaces named like GigabitEthernet0/1.10 (encapsulation dot1Q).
>>
>> It need reconfiguration to use 2x1G port-channles. I already did such reconfiguration
>> for same 7201 router with small number of sub-interfaces and know this is doable
>> changing sub-interfaces from GigabitEthernet0/1.N to Port-channel1.N
>>
>> This time the router has about 800 sub-interfaces. I can do some scripting
>> to prepare incremental configuration removing/re-creating sub-interfaces,
>> but I presume high CPU load for router while reconfiguring, long procedure time
>> and notable service degradation or even interruption.
>>
>> Is there same another, more lightweight way to mass-rename sub-interfaces
>> while switching from single parent interface to Port-channel?
> 
> Hi Eugene,
> 
> If you don't want to do this over a series of incremental changes then
> you can make one "big bang" change by taking a copy of the running
> configuration, making all the changes to that, and uploading it to the
> router as a replacement start-up config file, then just reboot the
> router to apply the config in one action. However, this approach is
> risky, you need to test that new full configuration file (confirm that
> the change only relate to the interface renaming, and that there are
> no mistakes, typos, wrong VLAN numbers etc.), which is quite tricky.
> 
> If you've ever wanted a pet project to get you into some network
> automation and programming stuff this sounds like an ideal project to
> me. You can definitely do this with Python tools like NAPALM and
> Nornir. Then you can automate the changes and automate the testing of
> the changes, and the rollback if required, in either multiple stages
> or as one giant change; whatever suits your circumstances best.

I've already wrote my script using AWK, it took moderate amount of time
to write and debug; it resulted in less than 50 lines. For each sub-interface
it removes all "ip route" commands referring to it (if any) then removes the interface,
then adds it back with new name, then re-adds removed routes changing interface name.

It's quick-n-dirty but works and is fine for one-time job.

My question was if IOS has some better way to rename sub-interfaces I could be unaware of.