1.3.1 Internet protocol (IP)

<Structure of this section>

(1) IP Packet Format

The formats and settings of IP packets sent by the Switch conform to RFC791 and RFC2474.

(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 1-1 Items checked in IP packet header
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	The total length must be equal to or greater than the header length multiplied by 4.	OK	NG
Packet identifier	Not checked.	-	-
Flag	Not checked.	-	-
Fragment offset	Not checked.	-	-
TTL	The TTL of the packets when the destination is the local device: Not checked.	-	-
TTL	The TTL of the packets to be forwarded: TTL-1 must be greater than 0.	OK	OK^#
Protocol	Not checked.	-	-
Header checksum	The header checksum must be correct.	OK	NG
Source address	Not checked.	-	-
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). The network number is a value other than 0 (except 0.0.0.0).	OK	NG

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

#: An ICMP Time Exceeded message is sent.

(3) IP Optional Supported Specifications

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

Table 1-2 IP Optional Supported Specifications
IP option	Type of IP packet
IP option	To the originating station of the Switch Packet	With the Switch arriving at the station Packet	Relay by the Switch Packet
End of Option List	OK	-	-
No Operation	OK	-	-
Loose Source Routing	OK	OK	OK
Strict Source Routing	NG	OK	OK
Record Route	OK	OK	OK
Internet Timestamp	NG	OK	OK

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