IP
V
6 ACL
S
23-13
Command Usage
• All new rules are appended to the end of the list.
• A flow label is assigned to a flow by the flow's source node. New flow
labels must be chosen pseudo-randomly and uniformly from the range
1 to FFFFF hexadecimal. The purpose of the random allocation is to
make any set of bits within the Flow Label field suitable for use as a
hash key by routers, for looking up the state associated with the flow.
• A flow identifies a sequence of packets sent from a particular source
to a particular (unicast or multicast) destination for which the source
desires special handling by the intervening routers. The nature of that
special handling might be conveyed to the routers by a control
protocol, such as a resource reservation protocol, or by information
within the flow's packets themselves, e.g., in a hop-by-hop option. A
flow is uniquely identified by the combination of a source address and
a non-zero flow label. Packets that do not belong to a flow carry a flow
label of zero.
• Hosts or routers that do not support the functions specified by the
flow label must set the field to zero when originating a packet, pass the
field on unchanged when forwarding a packet, and ignore the field
when receiving a packet.
• Optional internet-layer information is encoded in separate headers
that may be placed between the IPv6 header and the upper-layer
header in a packet. There are a small number of such extension
headers, each identified by a distinct Next Header value. IPv6 supports
the values defined for the IPv4 Protocol field in RFC 1700, including
these commonly used headers:
0 : Hop-by-Hop Options (RFC 2460)
6 : TCP Upper-layer Header (RFC 1700)
17 : UDP Upper-layer Header (RFC 1700)
43 : Routing (RFC 2460)
44 : Fragment (RFC 2460)
51 : Authentication (RFC 2402)
50 : Encapsulating Security Payload (RFC 2406)
60 : Destination Options (RFC 2460)
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