IP Normalizations

#	IP Field	Normalization Performed
1	Version	Non-IPv4 packets dropped.
2	Header Len	Drop if hdr_len too small.
3	Header Len	Drop if hdr_len too large.
4	Diffserv	Clear field.
5	ECT	Clear field.
6	Total Len	Drop if tot_len > link layer len.
7	Total Len	Trim if tot_len < link layer len.
8	IP Identifier	Encrypt ID.$\dagger$
9	Protocol	Enforce specific protocols.$\dagger$
-	Protocol	Pass packet to TCP,UDP,ICMP handlers.
10	Frag offset	Reassemble fragmented packets.
11	Frag offset	Drop if offset + len > 64KB.
12	DF	Clear DF.
13	DF	Drop if DF set and offset > 0.
14	Zero flag	Clear.
15	Src addr	Drop if class D or E.
16	Src addr	Drop if MSByte=127 or 0.
17	Src addr	Drop if 255.255.255.255.
18	Dst addr	Drop if class E.
19	Dst addr	Drop if MSByte=127 or 0.
20	Dst addr	Drop if 255.255.255.255.
21	TTL	Raise TTL to configured value.
22	Checksum	Verify, drop if incorrect.
23	IP options	Remove IP options.$\dagger$
24	IP options	Zero padding bytes.$\dagger$

$\dagger$ Indicates normalizations planned, but either not yet implemented or not yet tested at the time of writing.

Note that most normalizations are optional, according to local site policy.