Best way to force a TC=1 response?

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Best way to force a TC=1 response?

m3047
What's the best way to force an A query via UDP to return a TC=1 result:
a really long CNAME chain?

I want to set up a name that can be used in e.g. ping to perform an end
to end resolution check in application context.


The longer version is that there was a thread on postfix-users not too
long ago about the fact that MUSL libc doesn't do TCP (among other
things) and I want a way to test some hardware and statically built
apps. No jumbo frames here.

I was also mildly surprised to discover that glibc doesn't try TCP if
UDP fails to answer; for some reason I thought it did! Instead it
reports "Temporary failure in name resolution" in the ping example.

--

Fred Morris


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Re: Best way to force a TC=1 response?

John Levine
In article <[hidden email]> you write:
>What's the best way to force an A query via UDP to return a TC=1 result:
>a really long CNAME chain?

I'd suggest lots of AAAA records.  You could do it with A records but you'd
need four times as many

$ dig wordy.examp1e.com aaaa
;; Truncated, retrying in TCP mode.

; <<>> DiG 9.10.6 <<>> wordy.examp1e.com aaaa
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 24856
;; flags: qr rd ra ad; QUERY: 1, ANSWER: 187, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;wordy.examp1e.com. IN AAAA

;; ANSWER SECTION:
wordy.examp1e.com. 3594 IN AAAA 2001::1
wordy.examp1e.com. 3594 IN AAAA 2002::2
wordy.examp1e.com. 3594 IN AAAA 2003::3
wordy.examp1e.com. 3594 IN AAAA 2004::4
wordy.examp1e.com. 3594 IN AAAA 2005::5
wordy.examp1e.com. 3594 IN AAAA 2006::6
wordy.examp1e.com. 3594 IN AAAA 2006::7
wordy.examp1e.com. 3594 IN AAAA 2008::8
wordy.examp1e.com. 3594 IN AAAA 2009::9
wordy.examp1e.com. 3594 IN AAAA 200a::a
wordy.examp1e.com. 3594 IN AAAA 200b::b
wordy.examp1e.com. 3594 IN AAAA 200c::c
wordy.examp1e.com. 3594 IN AAAA 200d::d
wordy.examp1e.com. 3594 IN AAAA 200e::e
wordy.examp1e.com. 3594 IN AAAA 200f::f
wordy.examp1e.com. 3594 IN AAAA 2010::10
wordy.examp1e.com. 3594 IN AAAA 2011::11
wordy.examp1e.com. 3594 IN AAAA 2012::12
wordy.examp1e.com. 3594 IN AAAA 2013::13
wordy.examp1e.com. 3594 IN AAAA 2014::14
wordy.examp1e.com. 3594 IN AAAA 2015::15
wordy.examp1e.com. 3594 IN AAAA 2016::16
wordy.examp1e.com. 3594 IN AAAA 2017::17
wordy.examp1e.com. 3594 IN AAAA 2018::18
wordy.examp1e.com. 3594 IN AAAA 2019::19
wordy.examp1e.com. 3594 IN AAAA 201a::1a
wordy.examp1e.com. 3594 IN AAAA 201b::1b
wordy.examp1e.com. 3594 IN AAAA 201c::1c
wordy.examp1e.com. 3594 IN AAAA 201d::1d
wordy.examp1e.com. 3594 IN AAAA 201e::1e
wordy.examp1e.com. 3594 IN AAAA 201f::1f
wordy.examp1e.com. 3594 IN AAAA 2020::20
wordy.examp1e.com. 3594 IN AAAA 2021::21
wordy.examp1e.com. 3594 IN AAAA 2022::22
wordy.examp1e.com. 3594 IN AAAA 2023::23
wordy.examp1e.com. 3594 IN AAAA 2024::24
wordy.examp1e.com. 3594 IN AAAA 2025::25
wordy.examp1e.com. 3594 IN AAAA 2026::26
wordy.examp1e.com. 3594 IN AAAA 2027::27
wordy.examp1e.com. 3594 IN AAAA 2028::28
wordy.examp1e.com. 3594 IN AAAA 2029::29
wordy.examp1e.com. 3594 IN AAAA 202a::2a
wordy.examp1e.com. 3594 IN AAAA 202b::2b
wordy.examp1e.com. 3594 IN AAAA 202c::2c
wordy.examp1e.com. 3594 IN AAAA 202d::2d
wordy.examp1e.com. 3594 IN AAAA 202e::2e
wordy.examp1e.com. 3594 IN AAAA 202f::2f
wordy.examp1e.com. 3594 IN AAAA 2030::30
wordy.examp1e.com. 3594 IN AAAA 2031::31
wordy.examp1e.com. 3594 IN AAAA 2032::32
wordy.examp1e.com. 3594 IN AAAA 2033::33
wordy.examp1e.com. 3594 IN AAAA 2034::34
wordy.examp1e.com. 3594 IN AAAA 2035::35
wordy.examp1e.com. 3594 IN AAAA 2036::36
wordy.examp1e.com. 3594 IN AAAA 2037::37
wordy.examp1e.com. 3594 IN AAAA 2038::38
wordy.examp1e.com. 3594 IN AAAA 2039::39
wordy.examp1e.com. 3594 IN AAAA 203a::3a
wordy.examp1e.com. 3594 IN AAAA 203b::3b
wordy.examp1e.com. 3594 IN AAAA 203c::3c
wordy.examp1e.com. 3594 IN AAAA 203d::3d
wordy.examp1e.com. 3594 IN AAAA 203e::3e
wordy.examp1e.com. 3594 IN AAAA 203f::3f
wordy.examp1e.com. 3594 IN AAAA 2040::40
wordy.examp1e.com. 3594 IN AAAA 2041::41
wordy.examp1e.com. 3594 IN AAAA 2042::42
wordy.examp1e.com. 3594 IN AAAA 2043::43
wordy.examp1e.com. 3594 IN AAAA 2044::44
wordy.examp1e.com. 3594 IN AAAA 2045::45
wordy.examp1e.com. 3594 IN AAAA 2046::46
wordy.examp1e.com. 3594 IN AAAA 2047::47
wordy.examp1e.com. 3594 IN AAAA 2048::48
wordy.examp1e.com. 3594 IN AAAA 2049::49
wordy.examp1e.com. 3594 IN AAAA 204a::4a
wordy.examp1e.com. 3594 IN AAAA 204b::4b
wordy.examp1e.com. 3594 IN AAAA 204c::4c
wordy.examp1e.com. 3594 IN AAAA 204d::4d
wordy.examp1e.com. 3594 IN AAAA 204e::4e
wordy.examp1e.com. 3594 IN AAAA 204f::4f
wordy.examp1e.com. 3594 IN AAAA 2050::50
wordy.examp1e.com. 3594 IN AAAA 2051::51
wordy.examp1e.com. 3594 IN AAAA 2052::52
wordy.examp1e.com. 3594 IN AAAA 2053::53
wordy.examp1e.com. 3594 IN AAAA 2054::54
wordy.examp1e.com. 3594 IN AAAA 2055::55
wordy.examp1e.com. 3594 IN AAAA 2056::56
wordy.examp1e.com. 3594 IN AAAA 2057::57
wordy.examp1e.com. 3594 IN AAAA 2058::58
wordy.examp1e.com. 3594 IN AAAA 2059::59
wordy.examp1e.com. 3594 IN AAAA 205a::5a
wordy.examp1e.com. 3594 IN AAAA 205b::5b
wordy.examp1e.com. 3594 IN AAAA 205c::5c
wordy.examp1e.com. 3594 IN AAAA 205d::5d
wordy.examp1e.com. 3594 IN AAAA 205e::5e
wordy.examp1e.com. 3594 IN AAAA 205f::5f
wordy.examp1e.com. 3594 IN AAAA 2060::60
wordy.examp1e.com. 3594 IN AAAA 2061::61
wordy.examp1e.com. 3594 IN AAAA 2062::62
wordy.examp1e.com. 3594 IN AAAA 2063::63
wordy.examp1e.com. 3594 IN AAAA 2064::64
wordy.examp1e.com. 3594 IN AAAA 2065::65
wordy.examp1e.com. 3594 IN AAAA 2066::66
wordy.examp1e.com. 3594 IN AAAA 2067::67
wordy.examp1e.com. 3594 IN AAAA 2068::68
wordy.examp1e.com. 3594 IN AAAA 2069::69
wordy.examp1e.com. 3594 IN AAAA 206a::6a
wordy.examp1e.com. 3594 IN AAAA 206b::6b
wordy.examp1e.com. 3594 IN AAAA 206c::6c
wordy.examp1e.com. 3594 IN AAAA 206d::6d
wordy.examp1e.com. 3594 IN AAAA 206e::6e
wordy.examp1e.com. 3594 IN AAAA 206f::6f
wordy.examp1e.com. 3594 IN AAAA 2070::70
wordy.examp1e.com. 3594 IN AAAA 2071::71
wordy.examp1e.com. 3594 IN AAAA 2072::72
wordy.examp1e.com. 3594 IN AAAA 2073::73
wordy.examp1e.com. 3594 IN AAAA 2074::74
wordy.examp1e.com. 3594 IN AAAA 2075::75
wordy.examp1e.com. 3594 IN AAAA 2076::76
wordy.examp1e.com. 3594 IN AAAA 2077::77
wordy.examp1e.com. 3594 IN AAAA 2078::78
wordy.examp1e.com. 3594 IN AAAA 2079::79
wordy.examp1e.com. 3594 IN AAAA 207a::7a
wordy.examp1e.com. 3594 IN AAAA 207b::7b
wordy.examp1e.com. 3594 IN AAAA 207c::7c
wordy.examp1e.com. 3594 IN AAAA 207d::7d
wordy.examp1e.com. 3594 IN AAAA 207e::7e
wordy.examp1e.com. 3594 IN AAAA 207f::7f
wordy.examp1e.com. 3594 IN AAAA 2080::80
wordy.examp1e.com. 3594 IN AAAA 2081::81
wordy.examp1e.com. 3594 IN AAAA 2082::82
wordy.examp1e.com. 3594 IN AAAA 2083::83
wordy.examp1e.com. 3594 IN AAAA 2084::84
wordy.examp1e.com. 3594 IN AAAA 2085::85
wordy.examp1e.com. 3594 IN AAAA 2086::86
wordy.examp1e.com. 3594 IN AAAA 2087::87
wordy.examp1e.com. 3594 IN AAAA 2088::88
wordy.examp1e.com. 3594 IN AAAA 2089::89
wordy.examp1e.com. 3594 IN AAAA 208a::8a
wordy.examp1e.com. 3594 IN AAAA 208b::8b
wordy.examp1e.com. 3594 IN AAAA 208c::8c
wordy.examp1e.com. 3594 IN AAAA 208d::8d
wordy.examp1e.com. 3594 IN AAAA 208e::8e
wordy.examp1e.com. 3594 IN AAAA 208f::8f
wordy.examp1e.com. 3594 IN AAAA 2090::90
wordy.examp1e.com. 3594 IN AAAA 2091::91
wordy.examp1e.com. 3594 IN AAAA 2092::92
wordy.examp1e.com. 3594 IN AAAA 2093::93
wordy.examp1e.com. 3594 IN AAAA 2094::94
wordy.examp1e.com. 3594 IN AAAA 2095::95
wordy.examp1e.com. 3594 IN AAAA 2096::96
wordy.examp1e.com. 3594 IN AAAA 2097::97
wordy.examp1e.com. 3594 IN AAAA 2098::98
wordy.examp1e.com. 3594 IN AAAA 2099::99
wordy.examp1e.com. 3594 IN AAAA 209a::9a
wordy.examp1e.com. 3594 IN AAAA 209b::9b
wordy.examp1e.com. 3594 IN AAAA 209c::9c
wordy.examp1e.com. 3594 IN AAAA 209d::9d
wordy.examp1e.com. 3594 IN AAAA 209e::9e
wordy.examp1e.com. 3594 IN AAAA 209f::9f
wordy.examp1e.com. 3594 IN AAAA 20a0::a0
wordy.examp1e.com. 3594 IN AAAA 20a1::a1
wordy.examp1e.com. 3594 IN AAAA 20a2::a2
wordy.examp1e.com. 3594 IN AAAA 20a3::a3
wordy.examp1e.com. 3594 IN AAAA 20a4::a4
wordy.examp1e.com. 3594 IN AAAA 20a5::a5
wordy.examp1e.com. 3594 IN AAAA 20a6::a6
wordy.examp1e.com. 3594 IN AAAA 20a7::a7
wordy.examp1e.com. 3594 IN AAAA 20a8::a8
wordy.examp1e.com. 3594 IN AAAA 20a9::a9
wordy.examp1e.com. 3594 IN AAAA 20aa::aa
wordy.examp1e.com. 3594 IN AAAA 20ab::ab
wordy.examp1e.com. 3594 IN AAAA 20ac::ac
wordy.examp1e.com. 3594 IN AAAA 20ad::ad
wordy.examp1e.com. 3594 IN AAAA 20ae::ae
wordy.examp1e.com. 3594 IN AAAA 20af::af
wordy.examp1e.com. 3594 IN AAAA 20b0::b0
wordy.examp1e.com. 3594 IN AAAA 20b1::b1
wordy.examp1e.com. 3594 IN AAAA 20b2::b2
wordy.examp1e.com. 3594 IN AAAA 20b3::b3
wordy.examp1e.com. 3594 IN AAAA 20b4::b4
wordy.examp1e.com. 3594 IN AAAA 20b5::b5
wordy.examp1e.com. 3594 IN AAAA 20b6::b6
wordy.examp1e.com. 3594 IN AAAA 20b7::b7
wordy.examp1e.com. 3594 IN AAAA 20b8::b8
wordy.examp1e.com. 3594 IN AAAA 20b9::b9
wordy.examp1e.com. 3594 IN AAAA 20ba::ba
wordy.examp1e.com. 3594 IN AAAA 20bb::bb

;; Query time: 0 msec
;; SERVER: 192.168.80.2#53(192.168.80.2)
;; WHEN: Tue May 26 17:24:43 EDT 2020
;; MSG SIZE  rcvd: 5282

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Re: Best way to force a TC=1 response?

Mark Andrews


> On 27 May 2020, at 07:27, John Levine <[hidden email]> wrote:
>
> In article <[hidden email]> you write:
>> What's the best way to force an A query via UDP to return a TC=1 result:
>> a really long CNAME chain?
>
> I'd suggest lots of AAAA records.  You could do it with A records but you'd
> need four times as many

Well ~2 times as many.  Each additional A record requires 16 bytes and each
addition AAAA records requires 28 bytes.  That means ~256 A records and ~146
AAAA records to force TCP with a 4096 byte UDP buffer size.

John’s example had 187 AAAA records.

Mark
--
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742              INTERNET: [hidden email]

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