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Date: Wed, 7 Jul 2021 10:06:00 -0600
From: David Ahern <dsahern@...il.com>
To: Vadim Fedorenko <vfedorenko@...ek.ru>,
Stephen Hemminger <stephen@...workplumber.org>,
netdev@...r.kernel.org
Cc: David Ahern <dsahern@...nel.org>, Jakub Kicinski <kuba@...nel.org>
Subject: Re: Fw: [Bug 213669] New: PMTU dicovery not working for IPsec
On 7/7/21 9:52 AM, Vadim Fedorenko wrote:
> On 07.07.2021 15:07, Stephen Hemminger wrote:
>>
>>
>> Begin forwarded message:
>>
>> Date: Wed, 07 Jul 2021 09:08:07 +0000
>> From: bugzilla-daemon@...zilla.kernel.org
>> To: stephen@...workplumber.org
>> Subject: [Bug 213669] New: PMTU dicovery not working for IPsec
>>
>>
>> https://bugzilla.kernel.org/show_bug.cgi?id=213669
>>
>> Bug ID: 213669
>> Summary: PMTU dicovery not working for IPsec
>> Product: Networking
>> Version: 2.5
>> Kernel Version: 5.12.13
>> Hardware: x86-64
>> OS: Linux
>> Tree: Mainline
>> Status: NEW
>> Severity: high
>> Priority: P1
>> Component: IPV4
>> Assignee: stephen@...workplumber.org
>> Reporter: marek.gresko@...tonmail.com
>> Regression: No
>>
>> Hello,
>>
>> I have two sites interconnected using ipsec (libreswan)
>>
>> the situation is as follows:
>>
>> X <=> (a) <=> (Internet) <=> (b) <=> Y
>>
>> So you have two gateways a and b connected to the internet and their
>> corresponding internal subnets X and Y. The gateway a is connected to the
>> provider p using pppoe. The ipsec tunnel is created between a and b to
>> interconnect subnets X and Y. When gateway b with internal address y
>> itself is
>> communication to the gateway a using its internal address x. Addresses
>> x and y
>> are defined by leftsourceif and rightsourceip in the libreswan
>> configuration,
>> you get this behavior:
>>
>> b# ping -M do x -s 1392 -c 1
>> PING x (x.x.x.x) 1392(1420) bytes of data.
>>
>> --- ping statistics ---
>> 1 packets transmitted, 0 received, 100% packet loss, time 0ms
>>
>> b# ping -M do a -s 1460 -c 3
>> PING a (a.a.a.a) 1460(1488) bytes of data.
>> From p (p.p.p.p) icmp_seq=1 Frag needed and DF set (mtu = 1480)
>> ping: local error: message too long, mtu=1480
>> ping: local error: message too long, mtu=1480
>>
>> --- ping statistics ---
>> 3 packets transmitted, 0 received, +3 errors, 100% packet loss, time
>> 2014ms
>>
>> b# ping -M do x -s 1392 -c 3
>> PING x (x.x.x.x) 1392(1420) bytes of data.
>> ping: local error: message too long, mtu=1418
>> ping: local error: message too long, mtu=1418
>> ping: local error: message too long, mtu=1418
>>
>> --- ping statistics ---
>> 3 packets transmitted, 0 received, +3 errors, 100% packet loss, time
>> 2046ms
>>
>>
>> Legend:
>> x.x.x.x is an inner ip address if the gateway (a) (or x from the inside).
>> a.a.a.a is an outer address of the gateway (a).
>> p.p.p.p is some address in the provider's network of the (a) side.
>>
>> So definitely the ipsec tunnel is aware of the mtu only when some outer
>> communication is in progress. The inner communication itself is not
>> aware of
>> icmp packets using for PMTU discovery. I had also a situation when
>> also the
>> outer pings did not help the ipsec to be aware of the MTU and after
>> reboot it
>> started to behave like discribed again.
>>
>> Did I describe it understandably or should I clarify things?
>>
>> Thanks
>>
>> Marek
>>
>
> Looks like I didn't cover one more case in my MTU patch series. I'll try
> to look
> deeper
pmtu.sh test script covers xfrm (esp) cases with vti devices. Could add
more ipsec test cases to it.
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