netdev - Re: [PATCH net-next 2/3] net: ipv4: flush neighbor entries when carrier is off

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Date:   Tue, 7 Nov 2017 14:29:57 +0900
From:   David Ahern <dsahern@...il.com>
To:     Ido Schimmel <idosch@...sch.org>
Cc:     netdev@...r.kernel.org, jhs@...atatu.com,
        Satish Ashok <sashok@...ulusnetworks.com>
Subject: Re: [PATCH net-next 2/3] net: ipv4: flush neighbor entries when
 carrier is off

On 11/6/17 11:49 PM, David Ahern wrote:
>>> diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
>>> index f02819134ba2..aa8fea74858f 100644
>>> --- a/net/ipv4/fib_frontend.c
>>> +++ b/net/ipv4/fib_frontend.c
>>> @@ -1226,10 +1226,13 @@ static int fib_netdev_event(struct notifier_block *this, unsigned long event, vo
>>>  		break;
>>>  	case NETDEV_CHANGE:
>>>  		flags = dev_get_flags(dev);
>>> -		if (flags & (IFF_RUNNING | IFF_LOWER_UP))
>>> +		if (flags & (IFF_RUNNING | IFF_LOWER_UP)) {
>>>  			fib_sync_up(dev, RTNH_F_LINKDOWN);
>>> -		else
>>> +		} else {
>>>  			fib_sync_down_dev(dev, event, false);
>>> +			if (IN_DEV_IGNORE_ROUTES_WITH_LINKDOWN(in_dev))
>>
>> Can you please explain why the flushing is conditioned on this sysctl
>> being enabled? If carrier is down and the sysctl is enabled, then the
>> nexthop will not be used anyway.

you are right, of course. ;-) With the sysctl enabled nexthops with
linkdown have upper_bound set to -1 and will not get selected in
fib_select_multipath.

Jamal: the existing code with the sysctl's enabled should fix your use case.