89225d1ce6
i) RFC3810, 9.2. Query Interval [QI] says:
The Query Interval variable denotes the interval between General
Queries sent by the Querier. Default value: 125 seconds. [...]
ii) RFC3810, 9.3. Query Response Interval [QRI] says:
The Maximum Response Delay used to calculate the Maximum Response
Code inserted into the periodic General Queries. Default value:
10000 (10 seconds) [...] The number of seconds represented by the
[Query Response Interval] must be less than the [Query Interval].
iii) RFC3810, 9.12. Older Version Querier Present Timeout [OVQPT] says:
The Older Version Querier Present Timeout is the time-out for
transitioning a host back to MLDv2 Host Compatibility Mode. When an
MLDv1 query is received, MLDv2 hosts set their Older Version Querier
Present Timer to [Older Version Querier Present Timeout].
This value MUST be ([Robustness Variable] times (the [Query Interval]
in the last Query received)) plus ([Query Response Interval]).
Hence, on *default* the timeout results in:
[RV] = 2, [QI] = 125sec, [QRI] = 10sec
[OVQPT] = [RV] * [QI] + [QRI] = 260sec
Having that said, we currently calculate [OVQPT] (here given as 'switchback'
variable) as ...
switchback = (idev->mc_qrv + 1) * max_delay
RFC3810, 9.12. says "the [Query Interval] in the last Query received". In
section "9.14. Configuring timers", it is said:
This section is meant to provide advice to network administrators on
how to tune these settings to their network. Ambitious router
implementations might tune these settings dynamically based upon
changing characteristics of the network. [...]
iv) RFC38010, 9.14.2. Query Interval:
The overall level of periodic MLD traffic is inversely proportional
to the Query Interval. A longer Query Interval results in a lower
overall level of MLD traffic. The value of the Query Interval MUST
be equal to or greater than the Maximum Response Delay used to
calculate the Maximum Response Code inserted in General Query
messages.
I assume that was why switchback is calculated as is (3 * max_delay), although
this setting seems to be meant for routers only to configure their [QI]
interval for non-default intervals. So usage here like this is clearly wrong.
Concluding, the current behaviour in IPv6's multicast code is not conform
to the RFC as switch back is calculated wrongly. That is, it has a too small
value, so MLDv2 hosts switch back again to MLDv2 way too early, i.e. ~30secs
instead of ~260secs on default.
Hence, introduce necessary helper functions and fix this up properly as it
should be.
Introduced in 06da92283 ("[IPV6]: Add MLDv2 support."). Credits to Hannes
Frederic Sowa who also had a hand in this as well. Also thanks to Hangbin Liu
who did initial testing.
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Cc: David Stevens <dlstevens@us.ibm.com>
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
100 lines
2.7 KiB
C
100 lines
2.7 KiB
C
#ifndef LINUX_MLD_H
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#define LINUX_MLD_H
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#include <linux/in6.h>
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#include <linux/icmpv6.h>
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/* MLDv1 Query/Report/Done */
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struct mld_msg {
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struct icmp6hdr mld_hdr;
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struct in6_addr mld_mca;
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};
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#define mld_type mld_hdr.icmp6_type
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#define mld_code mld_hdr.icmp6_code
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#define mld_cksum mld_hdr.icmp6_cksum
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#define mld_maxdelay mld_hdr.icmp6_maxdelay
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#define mld_reserved mld_hdr.icmp6_dataun.un_data16[1]
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/* Multicast Listener Discovery version 2 headers */
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/* MLDv2 Report */
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struct mld2_grec {
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__u8 grec_type;
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__u8 grec_auxwords;
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__be16 grec_nsrcs;
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struct in6_addr grec_mca;
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struct in6_addr grec_src[0];
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};
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struct mld2_report {
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struct icmp6hdr mld2r_hdr;
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struct mld2_grec mld2r_grec[0];
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};
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#define mld2r_type mld2r_hdr.icmp6_type
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#define mld2r_resv1 mld2r_hdr.icmp6_code
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#define mld2r_cksum mld2r_hdr.icmp6_cksum
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#define mld2r_resv2 mld2r_hdr.icmp6_dataun.un_data16[0]
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#define mld2r_ngrec mld2r_hdr.icmp6_dataun.un_data16[1]
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/* MLDv2 Query */
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struct mld2_query {
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struct icmp6hdr mld2q_hdr;
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struct in6_addr mld2q_mca;
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#if defined(__LITTLE_ENDIAN_BITFIELD)
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__u8 mld2q_qrv:3,
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mld2q_suppress:1,
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mld2q_resv2:4;
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#elif defined(__BIG_ENDIAN_BITFIELD)
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__u8 mld2q_resv2:4,
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mld2q_suppress:1,
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mld2q_qrv:3;
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#else
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#error "Please fix <asm/byteorder.h>"
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#endif
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__u8 mld2q_qqic;
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__be16 mld2q_nsrcs;
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struct in6_addr mld2q_srcs[0];
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};
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#define mld2q_type mld2q_hdr.icmp6_type
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#define mld2q_code mld2q_hdr.icmp6_code
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#define mld2q_cksum mld2q_hdr.icmp6_cksum
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#define mld2q_mrc mld2q_hdr.icmp6_maxdelay
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#define mld2q_resv1 mld2q_hdr.icmp6_dataun.un_data16[1]
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/* Max Response Code, TODO: transform this to use the below */
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#define MLDV2_MASK(value, nb) ((nb)>=32 ? (value) : ((1<<(nb))-1) & (value))
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#define MLDV2_EXP(thresh, nbmant, nbexp, value) \
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((value) < (thresh) ? (value) : \
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((MLDV2_MASK(value, nbmant) | (1<<(nbmant))) << \
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(MLDV2_MASK((value) >> (nbmant), nbexp) + (nbexp))))
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#define MLDV2_MRC(value) MLDV2_EXP(0x8000, 12, 3, value)
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/* RFC3810, 5.1.3. Maximum Response Code:
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*
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* If Maximum Response Code >= 32768, Maximum Response Code represents a
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* floating-point value as follows:
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*
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* 0 1 2 3 4 5 6 7 8 9 A B C D E F
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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* |1| exp | mant |
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* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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*/
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#define MLDV2_MRC_EXP(value) (((value) >> 12) & 0x0007)
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#define MLDV2_MRC_MAN(value) ((value) & 0x0fff)
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/* RFC3810, 5.1.9. QQIC (Querier's Query Interval Code):
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*
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* If QQIC >= 128, QQIC represents a floating-point value as follows:
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*
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* 0 1 2 3 4 5 6 7
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* +-+-+-+-+-+-+-+-+
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* |1| exp | mant |
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* +-+-+-+-+-+-+-+-+
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*/
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#define MLDV2_QQIC_EXP(value) (((value) >> 4) & 0x07)
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#define MLDV2_QQIC_MAN(value) ((value) & 0x0f)
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#endif
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