From: wenxu <wenxu@ucloud.cn>
To: Jakub Kicinski <kuba@kernel.org>
Cc: netdev@vger.kernel.org
Subject: Re: [PATCH net] ip_tunnel: fix over-mtu packet send fail without TUNNEL_DONT_FRAGMENT flags
Date: Mon, 26 Oct 2020 16:23:29 +0800 [thread overview]
Message-ID: <c4dae63c-6a99-922e-5bd0-03ac355779ae@ucloud.cn> (raw)
In-Reply-To: <20201023141254.7102795d@kicinski-fedora-PC1C0HJN.hsd1.ca.comcast.net>
On 10/24/2020 5:12 AM, Jakub Kicinski wrote:
> On Wed, 21 Oct 2020 17:21:55 +0800 wenxu@ucloud.cn wrote:
>> From: wenxu <wenxu@ucloud.cn>
>>
>> The TUNNEL_DONT_FRAGMENT flags specific the tunnel outer ip can do
>> fragment or not in the md mode. Without the TUNNEL_DONT_FRAGMENT
>> should always do fragment. So it should not care the frag_off in
>> inner ip.
> Can you describe the use case better? My understanding is that we
> should propagate DF in normally functioning networks, and let PMTU
> do its job.
Sorry for relying so late. ip_md_tunnel_xmit send packet in the collect_md mode.
For OpenVswitch example, ovs set the gre port with flags df_default=false which will not
set TUNNEL_DONT_FRAGMENT for tun_flags.
And the mtu of virtual machine is 1500 with default. And the tunnel underlay device mtu
is 1500 default too. So if the size of packet send from vm + underlay length > underlay device mtu.
The packet always be dropped if the ip header of packet set flags with DF.
In the collect_md the outer packet can fragment or not should depends on the tun_flags but not inner
ip header like vxlan device did.
>> Fixes: cfc7381b3002 ("ip_tunnel: add collect_md mode to IPIP tunnel")
>> Signed-off-by: wenxu <wenxu@ucloud.cn>
>> ---
>> net/ipv4/ip_tunnel.c | 3 ---
>> 1 file changed, 3 deletions(-)
>>
>> diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
>> index 8b04d1d..ee65c92 100644
>> --- a/net/ipv4/ip_tunnel.c
>> +++ b/net/ipv4/ip_tunnel.c
>> @@ -608,9 +608,6 @@ void ip_md_tunnel_xmit(struct sk_buff *skb, struct net_device *dev,
>> ttl = ip4_dst_hoplimit(&rt->dst);
>> }
>>
>> - if (!df && skb->protocol == htons(ETH_P_IP))
>> - df = inner_iph->frag_off & htons(IP_DF);
>> -
>> headroom += LL_RESERVED_SPACE(rt->dst.dev) + rt->dst.header_len;
>> if (headroom > dev->needed_headroom)
>> dev->needed_headroom = headroom;
>
next prev parent reply other threads:[~2020-10-26 8:23 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-21 9:21 [PATCH net] ip_tunnel: fix over-mtu packet send fail without TUNNEL_DONT_FRAGMENT flags wenxu
2020-10-23 21:12 ` Jakub Kicinski
2020-10-26 8:23 ` wenxu [this message]
2020-10-26 20:56 ` Jakub Kicinski
2020-10-27 14:51 ` David Ahern
2020-10-27 15:55 ` Jakub Kicinski
2020-10-29 2:30 ` wenxu
2020-10-30 1:14 ` Jakub Kicinski
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