ServerIron ADX Security Guide 77
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Enabling strict TCP or UDP mode for flow-based ACLs 2
NOTE
Regardless of whether the strict mode is enabled or disabled, the device always compares TCP
control packets against the configured ACLs before creating a session entry for forwarding the
traffic.
NOTE
If the device's configuration currently has ACLs associated with interfaces, remove the ACLs from the
interfaces before changing the ACL mode.
To enable the strict ACL TCP mode, enter the following command at the global CONFIG level of the
CLI.
ServerIronADX(config)# ip strict-acl-tcp
Syntax: [no] ip strict-acl-tcp
This command configures the device to compare all TCP packets against the configured ACLs
before forward ing them.
To disable the strict ACL mode and return to the default ACL behavior, enter the following
command.
ServerIronADX(config)# no ip strict-acl-tcp
NOTE
Enter the ip rebind-acl command at the global CONFIG level of the CLI to place the ip strict-acl-tcp or
no ip strict-acl-tcp command into effect.
Enabling strict UDP mode
By default, when you use ACLs to filter UDP traffic, the Brocade device does not compare all UDP
packets against the ACLs. Instead, the device compares the source and destination information
against entries in the session table. The session table contains forwarding entries based on Layer
3 and Layer 4 information:
•If the session table contains a matching entry, the device forwards the packet, assuming that
the first packet the device received that contains the same address information was permitted
by the ACLs.
•If the session table does not contain a matching entry, the device sends the packet to the CPU,
where the software compares the packet against the ACLs. If the ACLs permit the packet
(explicitly by a permit ACL entry or implicitly by the absence of a deny ACL entry), the CPU
creates a session table entry for the packet’s forwarding information and forwards the packet.
For tighter control, the software provides the strict ACL UDP mode. When you enable strict UDP
processing, the device sends every UDP packet to the CPU and compares the packet against the
configured ACLs.
NOTE
If the device's configuration currently has ACLs associated with interfaces, remove the ACLs from the
interfaces before changing the ACL mode.
To enable the strict ACL UDP mode, enter the following command at the global CONFIG level of the
CLI.
ServerIronADX(config)# ip strict-acl-udp