D-Link DVX-1000 User Manual page 39

DVX-1000 User Manual
21.2.2.15 ICMP Destination Unreachable/Service Unavailable Messages
The Destination Unreachable message is an ICMP message which is generated by the
router to inform the client that the destination host is unreachable, unless the
datagram has a multicast address. Reasons for this message may include the
physical connection to the host does not exist (distance is infinite), the indicated
protocol or port is not active, or the data must be fragmented but the 'don't
fragment' flag is on.This message is allowed.
21.2.2.16 ICMP Time Exceeded Messages
The ICMP time exceeded message is generated when the gateway processing the
datagram (or packet, depending on how you look at it) finds the Time To Live field
(this field is in the IP header of all packets) is equal to zero and therefore must be
discarded. The same gateway may also notify the source host via the time exceeded
message.
21.2.2.17 ICMP Ping
ICMP echo request and echo reply messages are allowed, by default.
21.2.2.18 Connections to SOCKS, X-Windows, Open-Windows & NFS ports
The ports to SOCKS, X-Windows, Open-Windows and NFS are blocked, by default, so
as to protect the system from protocol and system administration problems.
21.2.2.19 Telnet/SSH/FTP/HTTP/HTTPS/TFTP Server/Client
The settings related to either of Telnet/SSH/FTP/HTTP/HTTPS/TFTP server/client can
be altered as required.
21.2.2.20 NTP Client
The setting for allowing the packets related to NTP Client can be modified as
required. Currently, these packets are allowed.
21.2.2.21 Packets having source address as target system's external IP address
For natural reasons, such packets are blocked.
21.2.2.22 Packets from machine having private class-A/B/C addresses
Packets from either of the private class A, class B, or class C address received on the
external interface are blocked. Since these address can only be assigned to LANs.
21.2.2.23 Packets having source IP address as loopback address
Packets claiming to have loopback address as the source IP address are blocked.
21.2.2.24 Malformed broadcast packets
Malformed broadcast packets are blocked. The packets having "0.0.0.0" as the
destination address and/or "255.255.255.255" as the source address are dropped.
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