As a follow-up to my previous email- it seems the current implementation
of ipv6 tc filters in iproute2 is based on the obsolete RFC 1883 in
which bits 4-7 of the IPv6 header were the 'priority'.
If this is the case, I would recommend the change suggested below or a
new filter for trafficclass that took the bits 4-11 into account for
matching against traffic class of the packet.
Devanshu
------------------------------------------------------------------------
Subject:
IPv6 priority in tc filter
From:
Devanshu Mehta <mehta@xxxxxxxxxx>
Date:
Tue, 20 Dec 2005 16:26:46 -0500
To:
lartc@xxxxxxxxxxxxxxx
To:
lartc@xxxxxxxxxxxxxxx
Hi,
I have recently started to use 'tc' on ipv6 traffic and have come
across an issue with tc filter. As per tc_filter.c in iproute2-050816,
to match 'priority' of an ipv6 packet, the u32 filter matches against
the first 8 bits of the packet.
From f_u32.c:
if (strcmp(*argv, "priority") == 0) {
NEXT_ARG();
res = parse_u8(&argc, &argv, sel, 0, 0);
goto done;
}
According to RFC2460 for IPv6 (http://www.ietf.org/rfc/rfc2460.txt),
the first 4 bits of the packet are the version number and the
subsequent 8 bits are the traffic class. Shouldn't the u32 filter be
matching against the 8 bits of the traffic class, not the 4bit
version+first 4bits of traffic class?
The reason this is relevant is because I am trying to match EF traffic
with a tc filter command:
tc filter add dev eth2.1070 parent 10: protocol ipv6 prio 1 u32 match
ip6 priority 0xb8 0xff flowid 10:1
i.e. 0xb8 for EF. This, however, does not match my EF packets. If I
send the following command:
tc filter add dev eth2.1070 parent 10: protocol ipv6 prio 1 u32 match
ip6 priority 0x6b 0xff flowid 10:1
then it actually does match EF packets. That is, it matches the 4 bits
of the version (IP v6) and the first 4 bits of the traffic class. I
believe, the code above should actually read:
if (strcmp(*argv, "priority") == 0) {
NEXT_ARG();
res = parse_u8(&argc, &argv, sel, 4, 0);
goto done;
}
though I may be mistaken as to the actual syntax of parse_u8().
------------------------------------------------------------------------
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