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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.


next up previous
Next: UDP Normalizations Up: Normalizations performed by norm Previous: Normalizations performed by norm
Vern Paxson
2001-05-22