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Date:      Wed, 13 Jun 2018 10:41:25 -0700
From:      Michael Sierchio <kudzu@tenebras.com>
To:        "freebsd-net@freebsd.org" <freebsd-net@freebsd.org>,  "freebsd-ipfw@freebsd.org" <freebsd-ipfw@freebsd.org>
Subject:   Re: In-kernel NAT [ipfw] dropping large UDP return packets
Message-ID:  <CAHu1Y71umFx9w7uGiqjZ0ECQHkmbC3-WNryaYW4Vt3sWTFRKbg@mail.gmail.com>
In-Reply-To: <918b13e0-aef5-add2-6f5c-530bb5850a3a@wagsky.com>
References:  <a00fd38d-a2d1-fcb5-f46a-03ea3fe4d686@wagsky.com> <CAHu1Y71StwG1F1b41vpvBcFzxBZD0_Krm0G1VAGQj-mn%2B7DqWg@mail.gmail.com> <918b13e0-aef5-add2-6f5c-530bb5850a3a@wagsky.com>

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I see you have a case of Netgraph. Perhaps Julian will chime in.

On Wed, Jun 13, 2018 at 10:32 AM, Jeff Kletsky <freebsd@wagsky.com> wrote:

> On 6/13/18 10:22 AM, Michael Sierchio wrote:
>
> On Wed, Jun 13, 2018 at 10:16 AM, Jeff Kletsky <freebsd@wagsky.com> wrote=
:
>>
>> When a T-Mobile "femto-cell" is trying to establish its IPv4, IPSEC tunn=
el
>>
>>> to the T-Mobile provisioning servers, the reassembled, 4640-byte return
>>> packet is silently dropped by the in-kernel NAT, even though it "matche=
s"
>>> the outbound packet from less than 100 ms prior.
>>>
>>
>>
>> Do you have a 'reass' rule before applying nat on inbound traffic?
>>
>> - M
>>
> Yes, at the start of the rule set.
>
> Reassembly confirmed to be working by wireshark examination of the ngtee
> "taps" shown
>
> $ sudo ipfw list
> 00001 deny ip from any to any recv ng*
> 00004 ngtee 100 ip from any to any proto udp dst-port 500,4500 in
> 00004 ngtee 100 ip from any to any proto udp frag in
> 00004 ngtee 110 ip from any to any proto udp dst-port 500,4500 out
> 00004 ngtee 110 ip from any to any proto udp frag out
> 00005 reass ip from any to any
> 00006 ngtee 101 ip from any to any proto udp dst-port 500,4500 in //
> reassembled in
> 00006 ngtee 101 ip from any to any proto udp frag in // never should be
> frags after reass
> 00006 ngtee 111 ip from any to any proto udp dst-port 500,4500 out //
> reass out
> 00006 ngtee 111 ip from any to any proto udp frag out // never should be
> frage after reass
> [...]
>
>
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>



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"Well," Brahma said, "even after ten thousand explanations, a fool is no
wiser, but an intelligent person requires only two thousand five hundred."

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