netdev - Re: Q: bad routing table cache entries

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Message-ID: <56953C27.4030405@stressinduktion.org>
Date:	Tue, 12 Jan 2016 18:47:19 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Stas Sergeev <stsp@...t.ru>
Cc:	netdev <netdev@...r.kernel.org>,
	Sowmini Varadhan <sowmini.varadhan@...cle.com>
Subject: Re: Q: bad routing table cache entries

On 12.01.2016 18:33, Stas Sergeev wrote:
> 12.01.2016 20:26, Hannes Frederic Sowa пишет:
>> On 12.01.2016 18:18, Stas Sergeev wrote:
>>> 12.01.2016 20:06, Hannes Frederic Sowa пишет:
>>>> On 12.01.2016 17:56, Stas Sergeev wrote:
>>>>> 12.01.2016 19:42, Stas Sergeev пишет:
>>>>> Also the rfc1620 you pointed, seems to be saying this:
>>>>>
>>>>>                    A Redirect message SHOULD be silently discarded if the
>>>>>                    new router address it specifies is not on the same
>>>>>                    connected (sub-) net through which the Redirect arrived,
>>>>>                    or if the source of the Redirect is not the current
>>>>>                    first-hop router for the specified destination.
>>>>>
>>>>> It seems, this is exactly the rule we were trying to find
>>>>> during the thread. And it seems violated, either. Unless I am
>>>>> mis-interpreting it, of course.
>>>>
>>>> If you read on you will read that with shared_media this exact clause (the first of those) is not in effect any more.
>>> OK. But how to get such a redirect to work, if (checked with
>>> tcpdump) the packets do not even go to eth0, but to "lo"?
>>
>> I don't know, the router must be on the same shared medium. I guess physical reconfiguration is required?
> It is same.
> Router 192.168.8.1 has just one ethernet port.
> And even on the 192.168.10.202 node I can do:
> # arp -a |grep "0.1"
> ? (192.168.0.1) at 14:d6:4d:1c:97:3d [ether] on eth0
> So even 0.1 is about to be reachable.
> Still nothing works.
> Should it work if 192.168.0.1 router, to which 8.1 redirects,
> has shared_media disabled?

Can you check with tcpdump? ping requires the router to also find a 
correct way back, so packet can get stuck at a lot of places. Also uRPF 
is maybe active which kind of defeats shared_media and please check 
netfilter.

Bye,
Hannes