On 10/24/2020 5:12 AM, Jakub Kicinski wrote:
> On Wed, 21 Oct 2020 17:21:55 +0800 we...@ucloud.cn wrote:
>> From: wenxu <we...@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 <we...@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;
>
