3Com S7902E, Configuration Manual

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An IPv4 ACL can have only one name. Whether to specify a name for an ACL is up to you. After creating
an ACL, you cannot specify a name for it, nor can you change or remove the name of the ACL.
The name of an IPv4 ACL must be unique among IPv4 ACLs. However, an IPv4 ACL and an IPv6 ACL
can share the same name.
IPv4 ACL Match Order
An ACL consists of multiple rules, each of which specifies different matching criteria. These criteria may
have overlapping or conflicting parts. This is where the order in which a packet is matched against the
rules comes to rescue.
Two match orders are available for IPv4 ACLs:
z
config : where packets are compared against ACL rules in the order in which they are configured.
z
auto : where depth-first match is performed. The term depth-first match has different meanings for
different types of ACLs.
Depth-first match for a basic IPv4 ACL
The following shows how your switch performs depth-first match in a basic IPv4 ACL:
1) Sort rules by VPN instance first and compare packets against the rule configured with a VPN
instance.
2) In case of a tie, sort rules by source IP address wildcard mask and compare packets against the
rule configured with more zeros in the source IP address wildcard.
3) If two rules are present with the same number of zeros in their source IP address wildcards,
compare packets against the rule configured first prior to the other.
A wildcard mask is in dotted decimal notation. Its binary value 0 means "match" and binary value 1
means "do not care", which contrast with the meanings of the values of a subnet mask. For example, a
wildcard mask of 0.0.0.255 corresponds to a subnet mask of 255.255.255.0.
Depth-first match for an advanced IPv4 ACL
The following shows how your switch performs depth-first match in an advanced IPv4 ACL:
1) Sort rules by VPN instance first and compare packets against the rule configured with a VPN
instance.
2) In case of a tie, look at the protocol carried over IP. A rule with no limit to the protocol type (that is,
configured with the ip keyword) has the lowest precedence. Rules each of which has a single
specified protocol type are of the same precedence level.