On 09.06.2018 15:26, Rodney W. Grimes wrote:
>> Author: ae
>> Date: Sat Jun  9 09:57:14 2018
>> New Revision: 334875
>> URL: https://svnweb.freebsd.org/changeset/base/334875
>> Log:
>>   Explicitly change the link state when we assingn an address.
>>   Since we are setting IFF_UP flag on SIOCSIFADDR, it is possible, that
>>   after this link state information still not initialized properly.
>>   This leads to problems with routing, since now interface has
>>   IFCAP_LINKSTATE capability and a route is considered as working only
>>   when interface's link state is in LINK_STATE_UP (see RT_LINK_IS_UP()
>>   macro).
> I was going to say something when the ability to up and down
> the loopback interfaces was added as it perturbed me but I
> could not put my finger on places it may cause problems so
> remained silent on the matter.
> Now that I see this issue, having lo0 go DOWN can kill a network
> that is using exported from lo0 into a routing protocol routes that 
> are used for management purposes.

This was one of the main reasons of this change.

> How does Cisco, Juniper, etc at handle this?
> Do any of them or all of them allow you to "down" loopback?

AFAIK, they allow this.

WBR, Andrey V. Elsukov

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