From: Stas Sergeev <stsp@list•ru>
To: Hannes Frederic Sowa <hannes@stressinduktion•org>
Cc: netdev <netdev@vger•kernel.org>,
Sowmini Varadhan <sowmini.varadhan@oracle•com>
Subject: Re: Q: bad routing table cache entries
Date: Tue, 12 Jan 2016 20:18:24 +0300 [thread overview]
Message-ID: <56953560.9050906@list.ru> (raw)
In-Reply-To: <569532A6.1070905@stressinduktion.org>
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:
>>> 12.01.2016 19:10, Hannes Frederic Sowa пишет:
>>>> On 12.01.2016 17:03, Stas Sergeev wrote:
>>>>> 12.01.2016 18:52, Hannes Frederic Sowa пишет:
>>>>>> On 12.01.2016 16:34, Hannes Frederic Sowa wrote:
>>>>>>> On 29.12.2015 11:54, Stas Sergeev wrote:
>>>>>>>> Hello.
>>>>>>>>
>>>>>>>> I was hitting a strange problem when some internet hosts
>>>>>>>> suddenly stops responding until I reboot. ping to these
>>>>>>>> host gives "Destination Host Unreachable". After the
>>>>>>>> initial confusion, I've finally got to
>>>>>>>> ip route get
>>>>>>>> and got something quite strange.
>>>>>>>>
>>>>>>>>
>>>>>>>> Example for GOOD address (the one that I can ping):
>>>>>>>>
>>>>>>>> ip route get 91.189.89.237
>>>>>>>> 91.189.89.237 via 192.168.8.1 dev eth0 src 192.168.10.202
>>>>>>>> cache
>>>>>>>>
>>>>>>>>
>>>>>>>> Example for BAD address (the one that stopped responding):
>>>>>>>>
>>>>>>>> ip route get 91.189.89.238
>>>>>>>> 91.189.89.238 via 192.168.0.1 dev eth0 src 192.168.10.202
>>>>>>>> cache <redirected>
>>>>>>>
>>>>>>> I tried to understand this thread and now wonder why this redirect route
>>>>>>> isn't there always. Can you please summarize again why this shouldn't
>>>>>>> happen? It looks totally fine to me from the configuration of your
>>>>>>> router and the subnet masks.
>>>>>>
>>>>>> Just an addendum:
>>>>>>
>>>>>> In IPv6 a redirect is seen as a notification telling hosts, this new address is on the same link as you. I think this semantic is the same for IPv4, so we are informing you that in essence you are
>>>>>> getting a /32 route installed to your new interface and can do link layer resolving of the new host.
>>>>>>
>>>>>> I do think this is valid and fine.
>>>>> You can't call "valid and fine" something that doesn't
>>>>> work, at first place. Why and where does it fail, was the
>>>>> subject of this thread.
>>>>
>>>> In terms of the shared media specification <https://tools.ietf.org/html/rfc1620> it is valid and fine.
>>> Good luck sending users to RFC without giving any explanations. :)
>
> It explains how and what extensions need to be added to an ip routing/host device to deal better with shared media.
>
>>> Well, yes, an interesting reading, but:
>>> https://tools.ietf.org/html/rfc1812
>>> ---
>>> Routers MUST NOT generate a Redirect Message unless all the following
>>> conditions are met:
>>>
>>> o The packet is being forwarded out the same physical interface that
>>> it was received from,
>>>
>>> o The IP source address in the packet is on the same Logical IP
>>> (sub)network as the next-hop IP address, and
>>>
>>> o The packet does not contain an IP source route option.
>>>
>>> The source address used in the ICMP Redirect MUST belong to the same
>>> logical (sub)net as the destination address.
>>> ---
>>>
>>> Could you please explain why the above does not apply?
>> 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"?
And how to deal with the above quote from rfc1812?
> I don't know why shared_media=1 is the default in Linux, this decision was made long before I joined here. Anyway, with shared_media=1 this is absolutely the required behavior.
Then it should work. How? :)
next prev parent reply other threads:[~2016-01-12 17:18 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-29 10:54 Q: bad routing table cache entries Stas Sergeev
2015-12-29 11:58 ` Sowmini Varadhan
2015-12-29 12:06 ` Stas Sergeev
2015-12-29 12:32 ` Sowmini Varadhan
2015-12-29 12:43 ` Stas Sergeev
2015-12-29 13:19 ` Stas Sergeev
2015-12-29 15:22 ` Sowmini Varadhan
2015-12-29 15:38 ` Stas Sergeev
2015-12-29 17:40 ` Stas Sergeev
2015-12-30 12:42 ` Stas Sergeev
2015-12-30 14:17 ` Eric Dumazet
2015-12-30 17:56 ` David Miller
2016-01-04 1:05 ` Sowmini Varadhan
2016-01-04 1:32 ` Stas Sergeev
2016-01-04 17:23 ` Stas Sergeev
2016-01-12 14:40 ` Stas Sergeev
2016-01-12 14:47 ` Sowmini Varadhan
2016-01-12 20:33 ` David Miller
2016-01-12 15:34 ` Hannes Frederic Sowa
2016-01-12 15:52 ` Hannes Frederic Sowa
2016-01-12 16:03 ` Stas Sergeev
2016-01-12 16:10 ` Hannes Frederic Sowa
2016-01-12 16:42 ` Stas Sergeev
2016-01-12 16:56 ` Stas Sergeev
2016-01-12 17:06 ` Hannes Frederic Sowa
2016-01-12 17:18 ` Stas Sergeev [this message]
2016-01-12 17:26 ` Hannes Frederic Sowa
2016-01-12 17:33 ` Stas Sergeev
2016-01-12 17:47 ` Hannes Frederic Sowa
2016-01-12 20:43 ` Stas Sergeev
2016-01-12 22:26 ` Hannes Frederic Sowa
2016-01-12 22:57 ` Stas Sergeev
2016-01-12 23:07 ` Hannes Frederic Sowa
2016-01-13 12:59 ` Stas Sergeev
2016-01-12 17:41 ` Stas Sergeev
2016-01-12 15:57 ` Stas Sergeev
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