netdev - Re: [PATCH net] vrf: sit mtu should not be updated when vrf netdev is the link

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Date:   Mon, 6 May 2019 14:33:10 -0600
From:   David Ahern <dsahern@...il.com>
To:     Stephen Suryaputra <ssuryaextr@...il.com>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH net] vrf: sit mtu should not be updated when vrf netdev is
 the link

On 5/6/19 2:28 PM, Stephen Suryaputra wrote:
> On Mon, May 06, 2019 at 01:54:16PM -0600, David Ahern wrote:
>> On 5/6/19 1:00 PM, Stephen Suryaputra wrote:
>>> VRF netdev mtu isn't typically set and have an mtu of 65536. When the
>>> link of a tunnel is set, the tunnel mtu is changed from 1480 to the link
>>> mtu minus tunnel header. In the case of VRF netdev is the link, then the
>>> tunnel mtu becomes 65516. So, fix it by not setting the tunnel mtu in
>>> this case.
>>>
>>> Signed-off-by: Stephen Suryaputra <ssuryaextr@...il.com>
>>> ---
>>>  net/ipv6/sit.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
>>> index b2109b74857d..971d60bf9640 100644
>>> --- a/net/ipv6/sit.c
>>> +++ b/net/ipv6/sit.c
>>> @@ -1084,7 +1084,7 @@ static void ipip6_tunnel_bind_dev(struct net_device *dev)
>>>  	if (!tdev && tunnel->parms.link)
>>>  		tdev = __dev_get_by_index(tunnel->net, tunnel->parms.link);
>>>  
>>> -	if (tdev) {
>>> +	if (tdev && !netif_is_l3_master(tdev)) {
>>>  		int t_hlen = tunnel->hlen + sizeof(struct iphdr);
>>>  
>>>  		dev->hard_header_len = tdev->hard_header_len + sizeof(struct iphdr);
>>>
>>
>> can you explain how tdev is a VRF device? What's the config setup for
>> this case?
> 
> Hi David,
> 
> tdev is set to VRF device per your suggestion to my colleague back in
> 2017:
> 	https://www.spinics.net/lists/netdev/msg462706.html.
> Specifically this on this follow up:
> 	https://www.spinics.net/lists/netdev/msg463287.html
> 
> His basic config before your suggestion is available in:
> 	https://www.spinics.net/lists/netdev/msg462770.html
> 
> He and I had a refresher discussion this am trying to figure out if tdev
> should be a slave device. This is true if the local addr is specified.
> In this case the addr has to bound to a slave device. Then the underlay
> VRF can be derived from it. But if only remote is specified, then there
> isn't a straightforward way to associate the remote with a VRF unless
> tdev is set to a VRF device.
> 

Right. Thanks for the reminder.

Reviewed-by: David Ahern <dsahern@...il.com>