HP JetAdvantage Security Manager 10 Device E-LTU Instrukcja Użytkownika Pobierz pdf (Strona 70)

attribute accuracy confusion for recipients. RFC 2608 states “SLP is intended to function within

networks under cooperative administrative control. Such networks permit a policy to be implemented

regarding security, multicast routing and organization of services and clients into groups which are

not being feasible on the scale of the Internet as a whole”.

If SLP is not being used by HP Web Jetadmin or any other network application to discover HP printing

devices, it is recommended that it be disabled.

IPv4 Multicast

IPv4 multicast allows a device to transmit IP version 4 datagrams (messages) to a group of hosts

(multicast group address) on a TCP/IP network. In order to communicate, each device must be

configured to send and receive the datagram. IPv4 multicast allows a print device to be discovered by

a client utility that uses Bonjour (also known as mDNS) or service location protocol (SLP) for device

discovery. If you disable IPv4 Multicast, other protocols that use multicast, such as Bonjour and SLP,

might be disabled without notification.

In addition to traditional IP communication of a host sending packets to a “single host” via a unicast

transmission or to “all hosts” via a broadcast transmission, IP multicast enables communication to a

“subset of all hosts” as a group transmission. IP multicast uses an appropriately capable and

configured network environment to efficiently deliver a single packet to many receivers, without

requiring knowledge of the quantity or identity of the receivers. The most common protocol used in

multicast addressing is UDP (User Datagram Protocol), a connection-less method of communication

that excludes a packet delivery guarantee. Without packet delivery acknowledgement, network

bandwidth is additionally preserved. With multicast, switches and routers typically handle the

replication of a single packet to reach multiple receivers and determine the scalability of multicast in

the networked environment.

An IP multicast group address is used by sources and the receivers to “send” and “receive” multicast

messages. Sources use the group address as the IP destination address in their data packets.

Receivers that are interested in receiving packets sent to that group will normally join the group by

using the IGMP (Internet Group Management Protocol) protocol. The protocol most widely used to

“route” the multicast packet is PIM (Protocol Independent Multicast). Multicast is historically known as

a Class D address with address assignment ranging from 224.0.0.0 to 239.255.255.255. Every

packet that includes a destination address of 224.0.0.1 will receive a response from all multicast

enabled devices. HP Jetdirect utilizes a proprietary network device multicast address of 224.0.1.60

and UDP port 427. HP Web Jetadmin no longer possesses the ability to “actively” discover multicast

enabled HP devices. However, WJA can still discover devices by listening for SLP packets.

The efficiency of multicast does present security challenges. As mentioned, multicast transmitters

typically do not know the identity of its receivers. Packets are simply sent to the group address. Due

to lack of group address granularity, it is possible for receivers of one group to receive packets from

another. Since group addresses can never be used as source addresses, and group addresses aren’t

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HP JetAdvantage Security Manager 10 Device E-LTU Instrukcja Użytkownika Strona 70