31.1.2 Internet protocol (IP)

<Structure of this section>

(1) IP Packet Format

The format and settings of IP packets sent by the switch conform to RFC 791.

(2) IP packet header validity checking

The Switch checks the validity of the headers in IP packets when IP packets are received. The following table describes the IP packet header items that are checked.

Table 31-1 IP packet header check contents
IP packet header field	Check item	When a check error occurs Packet discard	Packet discard Send ICMP
Version	The version must be 4.	OK	NG
Header length	The header length must be equal to or greater than 5.	OK	NG
TOS	Not checked.	-	-
Total length	All of the following requirements apply: The total length must be equal to or greater than the header length multiplied by 4. Total length ≧ Actual size of received packet	OK	NG
Packet identifier	Not checked.	-	-
Flag	Not checked.	-	-
Fragment offset	Not checked.	-	-
TTL	Not checked.	-	-
Protocol	Not checked.	-	-
Header checksum	The header checksum must be correct.	OK	NG
Source address	All of the following requirements apply: Not a Class D address Not a class E address Not 255.255.255.255 The network number must not be 127 (internal loopback address). Network No. must not be 0*1	-	-
Destination address	All of the following requirements apply: Class A, Class B, Class C, or Class D The network number is a value other than 127 (127 is the internal loopback address). Network No. must not be 0*2	OK	NG

(Legend) OK: Do NG: Do not do-: Not apply

#1: Unless the destination address is 255.255.255.255, or the source and destination addresses are both 0.0.0.
#2: Except when the source and destination addresses are both 0.0.0.0.

(3) IP Optional Supported Specifications

The following table describes the IP options supported by the Switch.

Table 31-2 IP Option Support Specification
IP option	Type of IP packet
IP option	Packets sent by the Switch	Packets received by the Switch
End of Option List	OK	-
No Operation	OK	-
Loose Source Routing	OK	NG
Time stamp	NG	OK
Record Route	OK	OK
Strict Source Routing	NG	NG

(Legend) OK: Supported NG: Not supported-: No option processing