To provide protection from attacks, the Cisco ASA provides a feature called TCP normalization. TCP normalization is enabled by default and can detect abnormal packets. Once detected these packets can be either allowed, dropped or cleared of its abnormalities.
To configure the TCP normalizer changes are made within the tcp-map. The tcp-map is then assigned to a class-map. This class-map is then assigned to a policy-map which is then assigned to an interface via a service policy.
Within our example we will configure the ASA to permit the TCP header 34 (0x22).
tcp-map TCPMAP-PERMIT-0x22 tcp-options range 34 34 allow policy-map type inspect dns preset_dns_map parameters message-length maximum 512 policy-map global_policy class inspection_default inspect dns preset_dns_map inspect ftp inspect h323 h225 inspect h323 ras inspect rsh inspect rtsp inspect sqlnet inspect skinny inspect sunrpc inspect xdmcp inspect sip inspect netbios inspect tftp inspect ip-options class ALLOW-TCP-22 set connection advanced-options TCPMAP-PERMIT-0x22 service-policy global_policy global
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