netdev - Re: Question: should local address be expired when updating PMTU?

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Date:	Wed, 4 Feb 2015 09:59:54 +0800
From:	shengyong <shengyong1@...wei.com>
To:	Steffen Klassert <steffen.klassert@...unet.com>
CC:	<davem@...emloft.net>, <netdev@...r.kernel.org>,
	<yangyingliang@...wei.com>, <hannes@...hat.com>
Subject: Re: Question: should local address be expired when updating PMTU?



在 2015/2/3 20:01, Steffen Klassert 写道:
> On Tue, Feb 03, 2015 at 06:54:19PM +0800, shengyong wrote:
>>
>>
>> 在 2015/2/3 17:28, Steffen Klassert 写道:
>>> On Mon, Feb 02, 2015 at 04:20:24PM +0800, shengyong wrote:
>>>
>>> We first need to find out why you receive this Packet Too Big message,
>> The packet is sent by a commercial-off-the-shelf testcase, and I can reproduce the
>> situation by using scapy and creating a packet as the following:
>>
>> 	$ cat packet-too-big.py
>> 	#!/usr/bin/python
>> 	
>> 	from scapy.all import *
>>
>> 	# fe80::800:27ff:fe00:0 is linklocal addr of PC
>> 	# fe80::a00:27ff:fe1a:e2a0 is linklocal addr of VM
>> 	base=IPv6(src='fe80::800:27ff:fe00:0',dst='fe80::a00:27ff:fe1a:e2a0')
>> 	pkt_too_big=ICMPv6PacketTooBig(mtu=1024)
>> 	ext_base=IPv6(src='fe80::a00:27ff:fe1a:e2a0',dst='fe80::a00:27ff:fe1a:e2a0',plen=24)
>> 	ext_nd_na=ICMPv6ND_NA()
>> 	
>> 	packet=base/pkt_too_big/ext_base/ext_nd_na
>> 	send(packet)
> 
> So it is not a valid pmtu update, this make life easier.
> 
> Can you please test the patch below (compile tested only)?
Sorry, the later. I test it on 3.10-stable. It can fix this problem. So maybe this is a bug?
And the 3 approaches (different flags are used: RTF_LOCAL, IFF_LOOPBACK and RTF_CACHE) in
these mails can fix the expire of local address. I'm confused about these flags:
* RTF_LOCAL: the entries of local address, like address binded to the native NIC
* RTF_CACHE: all cached entries
* IFF_LOOPBACK: this is a device-related flag, which has the same meaning as RTF_LOCAL

Am I right? If so, I think RTF_LOCAL is appropriate, because we just want entries of local
addresses to be not expired and we don't care other entries (I think if they get expired,
a neigh discovery could find them back).

thx,
Sheng
> 
> This should fix your problem, and in combination with the two patches I sent
> out last week, it should cure the whole 'expiring of uncached routes' problem.
> 
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index 49596535..4ccfb9c 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -1156,7 +1156,8 @@ static void ip6_rt_update_pmtu(struct dst_entry *dst, struct sock *sk,
>  	struct rt6_info *rt6 = (struct rt6_info *)dst;
>  
>  	dst_confirm(dst);
> -	if (mtu < dst_mtu(dst) && rt6->rt6i_dst.plen == 128) {
> +	if (mtu < dst_mtu(dst) && rt6->rt6i_dst.plen == 128 &&
> +	    (rt6->rt6i_flags & RTF_CACHE)) {
>  		struct net *net = dev_net(dst->dev);
>  
>  		rt6->rt6i_flags |= RTF_MODIFIED;
> --
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> .
> 

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