netdev - Re: [PATCH net-next] net: ipv4: Add ability to have GRE ignore DF bit in IPv4 payloads

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Date:	Wed, 8 Jun 2016 00:23:39 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Philip Prindeville <philipp_subx@...fish-solutions.com>,
	netdev@...r.kernel.org
Cc:	Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: [PATCH net-next] net: ipv4: Add ability to have GRE ignore DF bit
 in IPv4 payloads

On 07.06.2016 22:42, Philip Prindeville wrote:
> On 06/07/2016 02:23 PM, Hannes Frederic Sowa wrote:
>>
>> On Tue, Jun 7, 2016, at 21:48, Philip Prindeville wrote:
>>>   static struct rtnl_link_ops ipgre_link_ops __read_mostly = {
>>> diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
>>> index d8f5e0a..95649eb 100644
>>> --- a/net/ipv4/ip_tunnel.c
>>> +++ b/net/ipv4/ip_tunnel.c
>>> @@ -682,7 +682,7 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct
>>> net_device *dev,
>>>       }
>>>         df = tnl_params->frag_off;
>>> -       if (skb->protocol == htons(ETH_P_IP))
>>> +       if (skb->protocol == htons(ETH_P_IP) && !tunnel->ignore_df)
>>>           df |= (inner_iph->frag_off&htons(IP_DF));
>>>         max_headroom = LL_RESERVED_SPACE(rt->dst.dev) + sizeof(struct
>>> iphdr)
>> Is still enforce that we inherit the ttl from the inner header to the
>> outer header if we don't set df bit?
>>
>> Thanks,
>> Hannes
> 
> That's correct.  That happens a few lines above and we don't change that
> behavior with this patch.

It should be discouraged to use this feature, but I have to admit that I
already used stripping of DF bit, too.

Acked-by: Hannes Frederic Sowa <hannes@...essinduktion.org>

Thanks,
Hannes