3Com MSR 50 Series Configuration Manual page 640

640 C 42: IP U
HAPTER NICAST
P R C
OLICY OUTING ONFIGURATION
There is an AND relationship between if-match clauses on a node. That is to say, a
packet must satisfy all matching rules specified by all if match clauses for the
node before the action specified by the apply clause is taken.
Currently, two types of if-match clause are available: if-match packet-length
and if-match acl. In each policy, you can specify only one if-match clause for
each type.
There are five types of apply clauses: apply ip-precedence, apply
output-interface, apply ip-address next-hop, apply default
output-interface, and apply ip-address default next-hop. You can specify
only one apply clause for each type in a policy. In the case that a packet satisfies
all if-match rules on a node, the priorities of these types of apply clauses are
ranked as follows:
apply ip-precedence: If configured, this clause will always be executed.
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apply output-interface and apply ip-address next-hop: The apply
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output-interface clause takes precedence over the apply ip-address
next-hop clause. This means that only the apply output-interface clause will
be executed when both are configured.
apply default output-interface and apply ip-address default next-hop:
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Alike, the apply default output-interface clause takes precedence over the
apply ip-address default next-hop clause. This means that only the apply
default output-interface clause is executed when both are configured. Either
of these two clauses is executed only when no outgoing interface or next hop
is defined for packets, or only when the defined outgoing interface or next hop
is invalid and the destination address does not have a corresponding route in
the routing table.
There is an OR relationship between nodes of a policy. That is, if a packet matches
a node, it satisfies the policy.
When configuring policy nodes, you need to specify the match mode as permit or
deny:
permit: Specifies the match mode as permit on a policy node. If a packet
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satisfies all rules defined by if-match clauses on the policy node, the apply
clauses are executed. If not, the packet will go to the next policy node for a
match.
deny: Specifies the match mode as deny on a policy node. When a packet
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satisfies all rules defined by if-match clauses on the policy node, the packet
will be rejected and will not go to the next policy node for a match.
A packet satisfying the match rules on a node will not go to the other nodes. If the
packet does not satisfy the match rules on any node, the packet will be forwarded
by means of looking up the routing table.
You can define two next hops or two outgoing interfaces at most for a policy. In
this way, packets are forwarded in turn from the two outgoing interfaces or two
next hops to achieve load sharing.
Follow these steps to configure policies: