Abstract:
Method for processing content of an Internet Protocol (IP) packet and method for processing a full broadcast IP packet. Processing content of an IP packet includes: extracting IP source and destination addresses and payload from the IP packet; and generating an IP frame encapsulating the IP source and destination addresses and the payload between a preamble field and an error checking field. Processing a full broadcast IP packet includes: receiving the full broadcast IP packet including an IP source address and a full broadcast IP destination address; ascertaining a closest matching IP address and a subnet thereof in a switching table of an IP switch; replacing the full broadcast IP destination address in the IP packet with a subnetted source address generated by applying the subnet mask to the IP source address; transmitting the IP packet to all IP addresses in the switching table within the subnetted source address.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method, a system and computer program for processing an IP packet, routing a structured data carrier, preventing broadcast storms, load-balancing and converting a full broadcast IP packet. 
     BACKGROUND OF THE INVENTION 
     The Internet is made of a combination of physical networks connected together by internetworking devices such as routers and gateways. Recent years have seen a vast increase in the variety and amount of content accessible on the Internet. However, as the traffic and file sizes downloaded from the Internet grow, the protocols underlying the operation of the Internet are becoming increasingly limiting. Referring to  FIG. 1 , let the Internet  1  comprise routers R 1 , R 2 , R 3  and R 4  connected by transmission lines L 1 , L 2 , L 3 , L 4  and L 5 . Let individual computers (hosts) D 1  and D 2  be connected to the Internet  1  through routers R 1  and R 4  respectively. Similarly, let a local area network (LAN)  2  comprise hosts D 3  to D 6  connected to a LAN switch S, which in turn is connected to the Internet through router R 2 . 
     Each host and router on a network is recognized by its logical address (e.g. an IP address), which encodes its network number and host number. Logical addresses are Internet work addresses whose jurisdiction is universal. However, traffic must pass through physical networks to reach a host. At the physical level, hosts and routers are recognized by their physical addresses. A physical address is a local address whose jurisdiction is a local network. A physical address should be unique locally, but not necessarily universally. A physical address is usually (but not always) implemented in hardware. Examples of physical addresses are 48-bit MAC addresses (in Ethernet) which are imprinted on a network interface card (NIC) installed in a host or router. 
     In a typical scenario, a host generates a message (e.g. a request or response) for transmission on the Internet  1 . The message is processed by a transport layer, which adds a header and passes the resulting packet to a network layer. The network layer adds its own header (including the logical addresses of the source and destination computers) to form a network layer packet (e.g. an IP packet). The packet is then sent to a data link layer, which adds its own header (comprising the physical addresses of the source and destination hosts) and checksum and passes the resulting frame to a physical layer at which point the host (e.g. D 1 ) transmits the frame to the nearest router (e.g. R 1 ). 
     On receipt of a frame, a router (e.g. R 1 ) strips the header and trailer from the frame and passes the packet located in the frame&#39;s payload to routing software. The routing software uses the packet header to choose an output line from the current router to forward the packet to nearest router (e.g. R 2 , R 3 ). This process is continued so that the packet is progressively moved through the Internet to the required destination. However, sometimes a message is too large to be encapsulated within a frame, in which case, the message must be fragmented and each piece thereof transported separately to its destination. Similarly, difficulties in synchronizing the operations at different layers leads to problems with inter alia unicast flooding (i.e. useless network traffic) which degrades the network performance. 
     For an Internet-based business (e.g. low-price airlines), a failure of any part of its computer system, for even a short period of time, will have a significant detrimental effect on its sales. In view of this, redundancy is being increasingly used to improve the reliability of a network by minimizing the impact of network faults. This usually involves duplicating routers, switches, and links to ensure continuity of service even during failures. 
     Layer 2 resiliency is achieved by providing multiple paths between different destinations. However, such multiple paths are prone to broadcast storms. The spanning-tree protocol (STP) was developed to prevent broadcast storms by breaking loops and rebuilding links between switches. However, even with improvements in this algorithm, it can still take 1-2 seconds for a topology to be modified. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method for processing of an Internet Protocol (IP) packet, said method comprising:
         extracting an IP source address and an IP destination address from the IP packet;   extracting a payload from the IP packet;   concatenating the IP source address, the IP destination address, and the payload to generate concatenated IP data comprising the IP source address, the IP destination address, and the payload; and   generating an IP frame, said generating the IP frame comprising encapsulating, within the IP frame, the concatenated IP data between a preamble field and an error checking field, wherein the preamble field identifies a start of the IP frame.       

     The present invention provides a computer program product comprising a storage medium having computer readable program code stored therein, said program code configured to be executed by a computer to cause the computer to perform a method for processing content of an Internet Protocol (IP) packet, said method comprising:
         extracting an IP source address and an IP destination address from the IP packet;   extracting a payload from the IP packet;   concatenating the IP source address, the IP destination address, and the payload to generate concatenated IP data comprising the IP source address, The IP destination address, and the payload; and   generating an IP frame, said generating the IP frame comprising encapsulating, within the IP frame, the concatenated IP data between a preamble field and an error checking field, wherein the preamble field identifies a start of the IP frame.       

     The present invention provides a method for processing a full broadcast Internet Protocol (IP) packet, said method comprising:
         providing an IP switch, wherein the IP switch comprises multiple ports and the switching table which is configured to comprise at least one entry, wherein the multiple ports comprise a plurality of access ports and a plurality of interswitch ports, wherein each access port is identified by a port identifier and is connected to a corresponding host in a Local Area Network (LAN), wherein the interswitch ports are configured to be statically connected to routers within the Internet to connect the routers together in connections that cannot be overwritten by a dynamic learning process, wherein each entry of the at least one entry comprises an IP address, a port identifier associated with the IP address and identifying a port of the multiple ports, and a route entry associated with the IP address, and wherein the IP switch does not comprise a Media Access Control (MAC) that associates a MAC address of each host in the LAN with each host&#39;s associated port identifier;   said IP switch receiving the full broadcast IP packet comprising an IP source address and a full broadcast IP destination address;   after said receiving the full broadcast IP packet, said IP switch reading the IP source address from the IP packet;   after said reading, said IP switch making a comparison between the IP source address with the IP addresses in the at least one entry of the switching table;   said IP switch ascertaining, from said comparison, a closest matching IP address in the at least one entry of the switching table that most closely matches the IP source address;   after said ascertaining, said IP switch determining a subnet mask of the closest matching IP address;   after said determining the subnet mask, said IP switch generating a subnetted source address by applying the subnet to the IP source address;   after said generating the subnetted source address, said IP switch replacing the full broadcast IP destination address in the IP packet with the subnetted source address; and   after said replacing, said IP switch transmitting the IP packet to all IP addresses in the switching table that are within the subnetted source address.       

     The present invention provides a computer program product comprising a storage medium having computer readable program code stored therein, said program code configured to be executed by a computer to cause the computer to perform a method for processing a full broadcast Internet Protocol (IP) packet, said method comprising:
         providing an IP switch, wherein the IP switch comprises multiple ports and the switching table which is configured to comprise at least one entry, wherein the multiple ports comprise a plurality of access ports and a plurality of interswitch ports, wherein each access port is identified by a port identifier and is connected to a corresponding host an a Local Area Network (LAN), wherein the interswitch ports are configured to be statically connected to routers within the Internet to connect the routers together in connections that cannot be overwritten by a dynamic learning process, wherein each entry of the at least one entry comprises an IP address, a port identifier associated with the IP address and identifying a port of the multiple ports, and a route entry associated with the IP address, and wherein the IP switch does not comprise a Media Access Control (MAC) table that associates a MAC address of each host in the LAN with each host&#39;s associated port identifier;   said IP switch receiving the full broadcast IP packet comprising an IP source address and a full broadcast IP destination address;   after said receiving the full broadcast IP packet, said IP switch reading the IP source address from the IP packet;   after said reading, said IP switch making a comparison between the IP source address with the IP addresses in the at least one entry of the switching table;   said IP switch ascertaining, from said comparison, a closest matching IP address in the at least one entry of the switching table that most closely matches the IP source address;   after said ascertaining, said IP switch determining a subnet mask of the closest matching IP address;   after said determining the subnet mask, said IP switch generating a subnetted source address by applying the subnet mask to the IP source address;   after said generating the subnetted source address, said IP switch replacing the full broadcast IP destination address in the IP packet with the subnetted source address; and   after said replacing, said IP switch transmitting the IP packet to all IP addresses in the switching table that are within the subnetted source address.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of computers connected to the Internet. 
         FIG. 2  is a block diagram of a conventional Ethernet frame. 
         FIG. 3A  is a block diagram of a conventional IP packet. 
         FIG. 3B  is a block diagram of a header in a conventional IP packet of  FIG. 3A . 
         FIG. 4  is a block diagram of a conventional LAN switch. 
         FIG. 5  is a block diagram of an IP frame in accordance with embodiments of the present invention. 
         FIG. 6  is a flowchart of the processing of an IP packet to produce the IP frame shown in  FIG. 5 , in accordance with embodiments of the present invention. 
         FIG. 7  is a block diagram of computers connected to the Internet through the IP switch in accordance with embodiments of the present invention. 
         FIG. 8  is a more detailed block diagram of the IP switch shown in  FIG. 7 , in accordance with embodiments of the present invention. 
         FIG. 9  is a flowchart of the dynamic learning procedure employed in an access port of the IP switch shown in  FIG. 7 , in accordance with embodiments of the present invention. 
         FIG. 10  is a flowchart of the DHCP option  43  snooping procedure employed in an access port of the IP switch shown in  FIG. 7 , in accordance with embodiments of the present invention. 
         FIG. 11  is a flowchart of the operation of a transport port in the IP switch shown in  FIG. 7 , in accordance with embodiments of the present invention. 
         FIG. 12  is a flowchart of the conversion of a full IP broadcast packet into a IP sub-netted broadcast IP frame by the IP switch shown in  FIG. 7 , in accordance with embodiments of the present invention. 
         FIG. 13  is a block diagram of a conventional session through an L4/L7 switch. 
         FIG. 14  is a block diagram of a conventional LAN switch looped arrangement. 
         FIG. 15  is a block diagram of a redundant router arrangement, in accordance with embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The data carrier will henceforth be known as an IP frame. Similarly, the Internet traffic routing device will be known as an IP switch. 
     A. Ethernet Protocol 
     Referring to  FIG. 2 , an Ethernet frame  10  comprises an eight byte preamble  12  (used to identify the start of a frame) and two Medium Access Channel (MAC) addresses  14 ,  16 , the first of which specifies the address of the destination of the frame (i.e. the destination address  14 ) and the second specifies the address of the source of the frame (i.e. the source address  16 ). 
     Following the destination and source addresses  14 ,  16 , the frame  10  comprises a frame type identifier  18  and a payload within a data field  10 . The data field  20  is of 46 to 1500 bytes long. The upper limit of 1500 bytes is based on the physical limitations of cables available when the Ethernet protocol was first developed. However, subsequent developments in cabling technologies mean that this limitation no longer applies. Nonetheless, the Ethernet protocol has not kept up with these developments. The data field  20  is followed by a four byte cyclic redundancy check (CRC) field  22 , which is used to detect errors in the frame  10 . 
     B. Internet Protocol 
     The Internet protocol is a network layer protocol in which data is transmitted in the form of packets. Referring to  FIG. 3A , an IP packet  30  comprises a header portion  32  (of variable length between 20-24 octets) and a text portion  34 , which contains the data payload. Referring to  FIG. 3B , the header portion  32  comprises fields: version  36 , Internet Header Length (IHL)  38 , and field  40  which specifies type of service and total length of the packet. The header portion  32  specifies inter alia the IP address of the source of the IP packet  30  (i.e. an IP source address  42 ) and the IP address of the intended destination of the IP packet  30  (i.e. an IP destination address  44 ). 
     An IP address encodes the network number and host number of every host and router on the Internet. An IP address can be set statically or dynamically via the Dynamic Host Configuration Protocol (DHCP). To obtain an IP address by DHCP, a newly booted computer broadcasts a DHCP discover packet. If a DHCP server receives the DHCP discover packet, it will check in its DHCP database and assign an available IP address thereto. The DHCP server will then return the DHCP address to the MAC-address of the requesting computer. 
     While an IP packet can be up to 64 Kbytes long, the data field of an Ethernet frame is only 1500 bytes long. Thus, to transmit a large IP packet under the Ethernet protocol, it may be necessary to divide the IP packet into a plurality of fragments that are small enough to be transmitted within an Ethernet frame. On reaching a given destination, the fragments are re-assembled to form the original payload of the IP packet. To facilitate the fragmentation process, an IP packet header  32  comprises a Dont Fragment (DF) flag  46  (which indicates whether or not the packet  30  may be fragmented) a More Fragment (MF) a fragment offset  48 , and an identification field  47  which identifies fragments derived from the same IP packet. 
     C. Traffic Routing Devices 
     C.1 LAN Switch 
     Referring to  FIG. 4 , a LAN switch  49  comprises a plurality of ports P 1 -P 4 , each of which is connectable to a LAN segment and associated computers D 1 -D 4 . The LAN switch  49  further comprises a high speed port  50  which connects the LAN switch  49  to other computers in the network. 
     When a LAN switch  49  first starts up and the computers D 1 -D 4  connected thereto request services from other computers, the switch  49  builds a table (known as MAC table)  51  that associates the MAC address of each local computer D 1 -D 4  connected thereto, with the number of the port P 1 -P 4  through which the computer is reachable. This ensures that if computer D 1  (connected to port P 1 ) needs to transmit to computer D 2  (connected to port P 2 ) the LAN switch  49  forwards the frames directly to the relevant ports (i.e. from port P 1  to port P 2 ), thereby sparing computers D 3 , D 4  connected to the other ports (P 3 , P 4 ) from having to respond to the frames intended for the computer D 2 . Similarly, if computer D 3  needs to send data to computer D 4  at the same time that computers D 1  and D 2  are communicating, the LAN switch  49  will forward frames from port P 3  to port P 4  at the same time as it forwards frames from port P 1  to port P 2 . 
     A switch directs a frame to an appropriate port by: 
     (a) determining the destination MAC address of the frame; 
     (b) comparing the destination MAC address with the addresses listed in the MAC table; 
     (c) finding a port number that corresponds with the destination MAC address; and 
     (d) transmitting the frame through the relevant port. 
     If a LAN switch  49  receives a frame comprising a destination MAC address that is not listed in the switch&#39;s MAC table  52 , the LAN switch  49  sends the (unicast) frame out through all of its ports (excluding the port from the frame originated) in a technique known as unicast flooding. On receipt of the packet, the destination host transmits an acknowledgement packet to the switch. The switch then adds the relevant MAC address (from the acknowledgement packet) to its MAC table  52 . 
     The LAN switch&#39;s MAC table  52  is populated statically or by a dynamic learning process. In the dynamic learning process, the LAN switch  49  compares an incoming frame&#39;s source address with the MAC addresses stored in the switch&#39;s MAC table  52 . If the source MAC address is not listed in the switch&#39;s MAC table  52 , the port number from which the frame was received and the frame&#39;s source MAC address are added to the MAC table  52 . The dynamic learning process may be conducted every time a frame is received, so that a movement of a computer to another port is automatically detected and the switch&#39;s MAC table  52  reconfigured accordingly. It is also possible to specify a lifetime for an entry in the switch&#39;s MAC table  52 , wherein after the expiry of the lifetime, the entry is removed from the switch&#39;s MAC table  52  and must be relearned. 
     C.2 IP Router 
     IP routers also direct Internet traffic. On receipt of an incoming frame, an IP router strips off the frame&#39;s header and examines the remaining IP packet to determine its IP destination address. This information is used together with optimal route details stored in a routing table in the router to determine the output line on which to transmit the packet. 
     Routing protocols (e.g. OSPF (Open Shortest Path First) and RIP (Routing Information Protocol)) enable routers to advertise and learn the most efficient routes to a given destination, to allow the routers to dynamically build and populate their routing tables. OSPF operates by assigning a cost (e.g. distance, delay etc.) to each path in a network and using these costs to compute the shortest path between a router and other nearby routers. OSPF also exchanges routing information between adjacent routers. In use, a router floods a “hello” message through all of its ports to identify its neighbors and then establishes a neighbourhood with adjacent routers and exchanges costs and tables therewith. 
     C.3 Default Gateway 
     Returning to  FIG. 1 , a default gateway is usually a router (R 2 ) that enables an end-host (e.g. D 3 ) to forward IP packets to the outside world (outside its LAN  2 ). From the above discussions of the Internet Protocol and Ethernet Protocol, it can be seen that even if the IP address of the default-gateway (R 2 ) is configured on all of its hosts (D 3 -D 6 ), the end-hosts (D 3 -D 6 ) use the Address Resolution Protocol (ARP) to determine the MAC address corresponding to the default gateway&#39;s IP address and encapsulate IP packets in Ethernet frames comprising the default-gateway MAC-address. 
     C.4 Address Resolution Protocol (ARP) 
     Physical and logical addresses are two different identifiers which are needed because an IP packet at the network layer may pass through different physical networks to reach its destination. As a result, it is necessary to be able to map a logical address to its corresponding physical address and vice versa. This can be done by either static or dynamic mapping. Static mapping means creating a table that associates a logical address with a physical address. This table is stored by each machine on a network. However, this approach is not ideal because physical addresses may change (e.g. if a host changes its NIC, or a mobile computer moves from one physical network to another). To implement these changes, a static mapping would have to be updated regularly, which would reduce network performance. 
     In dynamic mapping each time a machine knows one of the two addresses (logical or physical), it can use a protocol (e.g. Address Resolution Protocol (ARP)) to find the other one. When a host has a packet bound for another host on a locally connected Ethernet network (or a router receives a packet addressed to the local IP subnet), it will send a broadcast Ethernet frame containing an ARP request onto the Ethernet. An ARP request comprises the physical and logical addresses of the sender host and the logical address of the target (destination) host. All hosts with the same Ethernet broadcast address will receive the ARP request packet and examine it to compare the IP address it contains with the host&#39;s own IP address. If there is a match, the host will issue an ARP reply to the sender&#39;s MAC address and insert its own MAC address as the source of the reply. The sender host (or router) can then resolve the MAC-to-IP addressing and can send the original packet to the destination host using the destination host&#39;s proper MAC address. 
     If this process was to be repeated every time a packet was received from an external source, a LAN would be flooded with ARP broadcasts and replies. To avoid this situation, each host creates an ARP cache that monitors ARP requests and replies and builds a table of MAC and corresponding IP addresses. Because a host&#39;s IP address may change, either through manual configuration or automatic IP assignment (e.g. DHCP), the ARP cache must deactivate entries in the cache, typically every 4 hours (according to an ARP entry idle timeout variable) after creation. 
     Returning to  FIG. 1 , let a host D 2  (which may or may not be part of a LAN) attempt to send a data packet to host D 6  in LAN  2 . In this case, host D 2  must first send the data packet to router R 4  which transmits the packet to router R 2  through the Internet  1 . On receipt of the packet, the router R 2  uses its ARP table (not shown) to identify the correct MAC address of the recipient host D 6 . On determining the correct MAC address, the router R 2  transmits the packet to the switch S. The switch S then compares the MAC address of the desired recipient host D 6  with entries in its MAC table (not shown) to determine the correct port from which to transmit the packet so that it reaches the host D 6 . 
     As mentioned above, individual entries in a switch&#39;s MAC table and a router&#39;s ARP table have predefined timeout values (after which the entry must be relearned). An ARP table entry typically has a timeout value of about 4 hours (240 minutes), whereas a MAC table entry typically has a timeout value of about 5 minutes. Thus, the dynamic learning procedures employed in MAC and ARP tables are unlikely to be synchronized between routers and switches. Accordingly, there may be mismatches between the entries in each table. 
     In particular, if the router R 2  was unable to find a matching MAC address to the IP destination address of the packet from D 2 , the router R 2  would broadcast an ARP request packet to the switch S. On receipt of the ARP request packet, the switch S would broadcast the request through all of its ports and to all ports of any other switches. However, such flooding disturbs the performance of the network. To overcome this problem, synchronization of the ARP and MAC tables is needed. 
     D. Improved Frame Format 
     Referring to  FIG. 5 , an IP frame  54  comprises a four byte preamble field  112  (which is used to identify the start of the frame), in accordance with the embodiments of the present invention. The IP frame  54  further comprises an IP packet  130  with its associated IP header  132  (and IP source and destination addresses (not shown)) and IP text section  134 . Following the IP packet  130 , the IP frame  54  comprises a CRC checksum field  122 . 
     However, the IP frame  54  does not include the MAC source and destination addresses of a traditional Ethernet frame (as shown in  FIG. 2 ). Nor, does the IP frame  54  include the frame type identifier field of a traditional Ethernet frame. These omissions reduce the size of an IP frame  54  by fourteen bits, but more importantly ensure that the frame&#39;s payload is no longer subject to the 1500 byte limit normally provided under the Ethernet protocol. Accordingly, an IP packet can be encapsulated in its entirety within the IP frame  54  and transmitted without fragmentation and re-assembly. 
     Referring to  FIG. 6 , an IP frame is formed from an IP packet by the following steps:— 
     (a) extracting (step  55 ) the IP source and IP destination addresses from the IP packet; 
     (b) extracting (step  56 ) the text section from the IP packet; 
     (c) concatenating (step  57 ) the IP source and destination addresses and the text section to produce concatenated IP data; and 
     (d) encapsulating (step  58 ) the concatenated IP data between the preamble field and the CRC checksum field. 
     E. IP Switch 
     Since the IP frame does not comprise a MAC source and destination address, it can no longer be processed by a conventional LAN switch (in accordance with the data link layer). Instead, the IP frame is transported to its correct recipient by a routing device, namely an IP switch  60 . In effect, the IP switch  60  (see  FIG. 7 ) forwards IP packets based on their IP destination address, so that the MAC address table of a prior art LAN switch is no longer needed. Since a MAC source address, a MAC destination address, and a frame type identifier does not exist in the IP frame  54 , the IP switch  60  is not configured to process a MAC source address, a MAC destination address, and a frame type identifier. 
     Comparing  FIG. 1  with  FIG. 7 , it can be seen that the LAN switch S of  FIG. 1  is removed from a LAN  102  and replaced with an IP switch  60  to which the hosts D 3 -D 6  are directly connected. Similarly, the IP switch  60  is connected to other conventional routers or other IP switches. Thus, the IP switch  60  becomes a default gateway for the LAN  102 . The IP switch&#39;s ports are divided into interswitch (or transport ports) (I 1 -I 3 ) and IP access ports (A 1 -A 4 ). Interswitch ports (I 1 -I 3 ) are statically configured to connect routers together wherein these connections cannot be overwritten by a dynamic learning procedure. In contrast, routes through IP access ports (A 1 -A 4 ) are dynamically learned and can be overwritten depending on changing conditions in the network. In  FIG. 7 , the Internet  101  comprises routers R 1 , R 3 , and R 4 , which are connected to each other, to Interswitch ports I 1 , I 3 , and I 4 , respectively, and to the IP switch  60  by transmission lines L 1 , L 2 , L 3 , L 4 , and L 5  in the manner shown, In addition, routers R 1  and R 4 , are connected to hosts D 1  and D 2 , respectively. 
     By removing the layer 2 link between the hosts D 3 -D 6  and the router R 2 ; and replacing it with a single link between each host and the IP switch  60 , the separate ARP and MAC tables of the prior art LAN switch and IP router are replaced by a single IP switching table in the IP switch  60 , thereby avoiding the prior art problem of synchronizing ARP and MAC tables. Similarly, layer 2 loops and unicast flooding are avoided, as are, problems with fragmentation and address resolution. 
     Referring to  FIG. 8 , the IP switch  60  comprises a validator  56   e  for validating an incoming IP frame, an IP address reader  62  which reads the IP destination address of the incoming IP frame, and a comparator  64  which compares the IP destination address with the IP addresses in an archive, namely the IP switching table  66 . The IP switch  60  further comprises a port director  68  which directs an IP frame to a port (i.e., to an interswitch port or to an access port) whose port number corresponds with the matching entry in the switching table  66 . 
     F. Dynamic Learning Procedures in the IP Switch 
     The IP switching table in the IP switch  60  is populated with host IP addresses for each interface thereto, by means of: 
     1 (a) DHCP snooping (using DHCP Option  43  and well known Multicast IP@) by intercepting and interpreting DHCP server replies sent back to a host after the host has requested its IP address with a DHCP request; and 
     (b) a dynamic IP Learning procedure performed only on the IP switch&#39;s access port(s). 
     In broad overview, when an IP switch  60  dynamically discovers (via DHCP snooping or source IP address checking) that a new IP device is directly connected thereto, it adds an IP route entry to its IP switching table and advertises (using IP routing protocols such as OSPF) the new entry to its IP peers. The new entry has a lifetime and can be suppressed immediately when a link goes down or when a DHCP response is intercepted by the IP switch  60 . Regardless of whether it is learned by the dynamic learning procedure or the DHCP snooping procedure, an entry in the IP switching table will have an administrative distance of 0 (to represent a directly connected physical link). A more detailed discussion of the dynamic IP learning procedure and the DHCP snooping procedure follows below. 
     F.1 Dynamic IP Learning Procedure 
     Referring to  FIG. 9 , on receipt (step  70 ) from a host of an incoming IP frame on an access port, the IP switch validates (step  71 ) the CRC of the IP frame. Following validation, the IP switch reads (step  72 ) the IP source address from the IP frame. The IP switch then checks (step  73 ) whether the IP source address is present in its IP switching table. 
     If the IP source address of the IP frame is not present in the IP switching table, the IP source address (with subnet mask/32 to provide a route to a single host) is added (step  74 ) to the IP switching table, together with the number of the port on which the IP frame was received. The /32 subnet mask is included with the IP source address to ensure that the IP address only relates to the specifically identified host and not any other hosts. In particular, the couple (IP address, /32 subnet mask) is an IP subnet containing a single IP address. The administrative distance of the new entry is then set (step  75 ) to zero or to a pre-defined administrative distance threshold such as zero). 
     However, if the IP source address of the IP frame is present in the IP switching table, the administration distance of the entry in the IP switching table is checked  76 . If the administration distance of the entry is not equal to zero (i.e. the entry does not represent a directly connected route) or above a pre-defined administrative distance threshold (e.g. zero), then the IP source address of the IP frame is added (step  77 ) to the IP switching table (to maintain redundancy in the table) together with the subnet mask /32 and the number of the port on which the IP frame was received. The administration distance of the new entry is set (step  78 ) to zero or to a pre-defined administrative distance threshold such as zero). 
     If the IP source address of the incoming IP frame has a matching counterpart in the IP switching table and the administration distance is equal to zero (i.e. is the result of a static configuration) the port number of the entry is compared (step  79 ) with that of the port on which the IP frame was received. 
     If the port number of the entry in the switching table matches that of the port on which the IP frame was received, then step  82  is next executed. 
     If the port number of the entry in the switching table does not match that of the port on which the IP frame was received, it means that the source device was moved to another port. Accordingly, the entry in the IP switching table is overwritten (step  80 ) with the details of the incoming IP frame and port on which it was received. 
     The lifetime of the relevant entry in the IP switch is then reset (step  81 ). Thus, the entries in the IP switching table comprise the following variables: IP subnet (subnet address, subnet mask), [administrative distance/other routing protocol internal metric indicative of confidence in the entry], next hop (when possible), next interface. The administrative distance is indicative of a confidence in the entry&#39;s routing an IP frame from the port identified by to port identifier to the IP address of each entry. The confidence for the entry increases with decreasing administrative distance. An administrative distance of zero (“0”) is a smallest possible administrative distance and denotes a directly connected physical link. For example, the IP switching table could include the following entries: 
     172.17.0.0/16 is variably subnetted, 2 subnets, 2 masks 
     O IA 172.17.0.0/16 [110/11] via 9.100.112.132, 16:53:03, FastEthernet0/0 
     O IA 172.16.0.0/16 [110/2] via 9.100.112.134, 16:53:03, FastEthernet0/0 
     172.19.0.0/32 is subnetted, 2 subnets 
     O E2 172.19.147.138 [110/20] via 9.100.112.130, 16:53:03, FastEthernet0/0 
     O E2 172.19.147.134 [110/20] via 9.100.112.130, 16:53:03, FastEthernet0/0 
     In use, the IP destination address is then read (step  82 ) from the IP frame and compared (step  83 ) with those in the IP switching table. If multiple copies of the IP destination address are found in the IP switching table, the administration distances of the entries are compared (step  84 ) and the entry with the lowest administration distance is used to determine the number of the port from which to transmit the IP frame. The IP frame is then transmitted (step  85 ) from the relevant port of the modified IP switch. Similarly, if there is only one copy of the IP destination address in the IP switching table, the IP frame is transmitted (step  85 ) from the port corresponding thereto. 
     F.2. DHCP Option  43  Dynamic Learning Procedure 
     DHCP option  43  is a field in which an end-host can put an identifier in a DHCP request. At present a DHCP server checks the source MAC address of a DHCP request. However, with the IP switch, MAC addresses are not used any longer. Thus, it is necessary to use another identifier to enable a DHCP server to determine if a host is authorized to acquire an IP address therefrom (by means of a HTTP request). In particular, DHCP option  43  is used with a host identifier instead of a traditional source MAC address to identify the originator of a DHCP request and determine whether or not is entitled to acquire an IP address therefrom. For example, the host name could be used as a host identifier. 
     EXAMPLE 
     Option  43   
     Parameter Hostname: PC0012.officesite.country.companyname.com 
     As a result, the DHCP server will link the IP address it assigned with the hostname it received in the DHCP request. 
     In general, the main purposes of using option  43  in the DHCP request is to authenticate, validate, and account the DHCP client as described above; and to provide an IP address from an appropriate pool, range, or IP subnet. For example, if an option  43  DHCP request comprising the identifier hostname=pc.engineeringstaff.lab.ibm.com is received by a DHCP server, on detecting the option  43  value, the DHCP server could decide to offer an IP address in the subnet 12.12.12.0/24 because it has determined that this host relates to a member of the engineering staff. 
     Referring to  FIG. 10 , in broad overview, the method of populating the IP switching table of the IP switch using the DHCP option  43  dynamic learning procedure comprises the steps of: 
     transmitting (step  86 ) a DHCP option  43  request to a DHCP server; 
     intercepting (step  87 ) the DHCP response from the DHCP server; 
     extracting (step  88 ) the IP address from the DHCP response; and 
     adding (step  89 ) the IP address to the IP switching table. 
     G. Transmission from Interswitch Ports in the IP Switch 
     Interswitch ports are statically configured and do not undergo the above-described dynamic learning process. Accordingly, referring to  FIG. 11 , on receipt (step  90 ) from a router of an incoming IP frame on an interswitch port, the frame is validated (step  91 ) by means of its CRC. The IP destination address is then read (step  92 ) from the IP frame and compared (step  93 ) with the IP destination addresses (and associated subnet masks) in the IP switching table, to find the closest matching entry. The IP frame is then transmitted (step  94 ) from the port (i.e., from an access port or from an interswitch port) whose number is listed in the closest matching entry. 
     In summary, in contrast with the operations of a traditional LAN switch, the IP switch does not check for a protocol type of an incoming IP frame, nor does it check for the MAC addresses in the frame. 
     H. Applications of the IP Switch and IP Frame 
     H.1 Subnet Broadcast Addressing 
     Broadcast addressing refers to the ability to address a message that is broadcast to all hosts on a network. The destination address in a broadcast message consists of all ones (e.g. 0xFFFFFFFF). All stations automatically receive frames with this address. On IP networks, the IP address 255.255.255.255 is a general (or full) broadcast address. Packets with this address are in principle transmissible to all hosts on the Internet. However, it is also possible to broadcast a message to a smaller select group of hosts that are connected to a same sub-network. For example, on a (class C) network with IP address 192.168.1.0 the last byte designates a host address. However, a zero in this host address position does not refer to any given host, but instead provides a way of referring to the entire sub-network. The broadcast address for a specific network includes all ones in the host portion of its IP address. Thus, in the present example, packets with the sub-network broadcast IP address 192.168.1.255 are sent to all hosts on the sub-network. 
     In the IP switch, since it is no longer necessary to broadcast MAC addresses (to implement ARP), full IP broadcast addressing is no longer needed, since the first IP switch for a sub-network will manage the traffic for the sub-network. Thus, only sub-network broadcast IP addressing is required with the IP switch and there is no way of adding a full IP broadcast address to the switching table of the IP switch. 
     If an IP packet is received (from a conventional IP router), with a full IP broadcast address (255.255.255.255) as its IP destination address, there are a number of options available to the IP switch. In particular, the IP switch could redirect the received packet to all of its ports or drop the packet. Neither of these options is desirable. The first option is not particularly efficient insofar as it merely contributes to the amount of broadcast traffic on the network. The second option is undesirable because of the loss of potentially important information. A more desirable solution is for the IP switch to convert the full IP broadcast address to a sub-network broadcast IP address and redirect the modified packet to all the interfaces to hosts on the same relevant IP sub-network. 
     To this end, the IP switch could use a class-based subnetted broadcast of the IP address dynamically learned on the port where the broadcast had been received. For example, referring to  FIG. 12 , let a broadcast IP packet have an IP source address of 192.168.1.1 and a (full broadcast) IP destination address of 255.255.255.255. In the first steps, the IP switch reads (step  95 ) the IP source address of an IP frame and compares (step  96 ) it against the IP entries in its IP switching table. Let the IP switch have an IP route entry for the IP source address wherein the IP source address 192.168.1.1/32 is mapped to port  1 . The IP source address belongs to class C, whose subnet mask is 255.255.255.0 (/24). Thus, the corresponding subnet broadcast address will be 192.168.1.255. 
     Accordingly, the IP switch applies (step  97 ) the subnet mask to yield 192.168.1.255 and replaces (step  98 ) the full IP source broadcast address with the subnetted IP source address and transmits (step  99 ) the IP packet on all of the ports whose IP route entry (in the IP switching table) matches with the IP subnet 192.168.1.0/24 address. 
     If the IP switching table of the IP switch is populated using the DHCP snooping procedure, the DHCP reply from a DHCP server contains a given IP address and subnet mask. Thus, the IP switch could store the IP subnet mask to enable the translation of a full broadcast received on the relevant port to a subnetted IP broadcast, wherein the IP subnet mask found in the DHCP reply could be used to calculate the appropriate subnetted broadcast IP address as discussed above. 
     H.2 Avoiding Fragmentation Problems with the IP Frame 
     H.2(a) L4/L7 Switching 
     An L4/L7 switch enables the development of advanced network architectures by allowing routing and switching to be conducted based on information related to an application, rather than network addresses. L4/L7 switches can read application-level information in packet headers or payloads to enable the switch to intelligently distribute requests to the most suitable application server, based on geographic location, latency, application or server load. To provide this functionality, an L4/L7 switch employs network address translation (NAT) and higher layer addressing. 
     H.2(b) Network Address Translation (NAT) 
     NAT re-writes the source and/or destination addresses of IP packets as they pass through a router or firewall to enable multiple hosts on a private network to access the Internet using a single public IP address. Referring to  FIG. 13 , in a typical configuration, a local network  200  comprises a plurality of private hosts A 1 , A 2 , A 3 , each of which has a private IP address. The private hosts A 1 -A 3  are connected to a NAT device (i.e. a router)  202  which is connected in turn to the Internet  204 . 
     Let an internal private host A 1  attempt to contact an external host B with a packet HTTP(A 1 ,B). The NAT device  202  intercepts host A&#39;s outgoing packet and re-writes the source address (A 1 ) with a public virtual IP address (VIP 1 ) selected from a pool  205  of public addresses in the NAT device  202  and mapped as a temporary alias to the private host A&#39;s private IP address (A 1 ). The source address of the packet from host A 1  is re-written with the virtual IP address (VIP 1 ), to produce a new outgoing packet HTTP(VIP 1 , B) and a local session state is set up in the NAT device  202  for the mapping between the private and the virtual (public) addresses. After this mapping is made, all subsequent packets within this application stream, from this private IP address to the specified virtual address, will also have their source (private IP) address mapped to the virtual address in the same fashion. 
     On receipt of a response packet HTTP(B, VIP 1 ) from external host B, the NAT device  202  checks the destination address of the packet. If the destination address is stored in the NAT pool  205 , the NAT device  202  looks up its translation table and if it finds a corresponding table entry, maps the destination address (VIP 1 ) to the appropriate local private IP address (A 1 ). However, if there is no current mapping entry for the destination address, the packet is discarded. 
     It can be seen from the above, that a NAT device usually alters the IP source address of a request packet and the IP destination address of a reply packet thereto. The resulting packet is then routed through the networks in the Internet to its required destination. However, as a packet is routed through different networks, it may be necessary for an intermediate router (i.e. a gateway between different types of networks) to divide the packet into smaller pieces. This process (known as fragmentation) occurs when a router receives a packet larger than the maximum transmission unit (MTU) (i.e. the largest packet transferable in a network) of the next network segment. For example, if an attempt is made to transfer a large video file (of more than 1500 bytes) through a LAN (operating under the Ethernet protocol), the packet must be fragmented so that the individual fragments can be encapsulated in Ethernet frames and transported through the LAN. 
     If the DF bit of an IP packet is set to zero, an intermediate router can fragment the IP packet and the resulting fragments are received by the destination host and reassembled therein. However, if the DF bit in the IP packet is set to one, the intermediate router is not allowed to fragment the IP packet. In this case, there are two available options. In the first option, the intermediate router over-rides the prohibition on fragmentation (provided by the setting of the DF bit to one) and forces the fragmentation of the IP packet. However, this option is only used if a network administrator is sure of the type of traffic passing through the network device because forcing fragmentation can have a detrimental effect on the Internet stream. Thus, whilst in practice, this course of action is not recommended, nonetheless if used, it would have the same result as if the DF bit had originally been set to zero. 
     The other possibility is not to force the DF bit. In this case, the intermediate router cannot fragment the IP packet. Thus, the intermediate router drops the IP packet and returns an Internet Control Message Protocol (ICMP) packet (i.e. a protocol used between a host server and a gateway to the internet to send message control and error-reporting messages) to the source of the original IP packet. The ICMP message indicates that the original IP packet needs to be fragmented at the source because the DF bit is set to 1 (i.e. the IP packet cannot be fragmented at the intermediate router). However, because of the address translation activities of the L4/L7 switch, the source address of the packet is a virtual IP address. An L4/L7 switch does not manage ICMP messages. Thus, when the ICMP message (from the intermediate router) is received by the L4/L7 switch, the switch doesn&#39;t know to which host in the virtual local network  200  it should send the packet. Accordingly, the L4/L7 switch drops the ICMP message. Thus, the originating host (e.g. A 1 ) never gets the ICMP packet and unwittingly continues to send packets to the required destination server without fragmentation. Thus, the packets from the originating host continue to be dropped by the intermediate router and never reach the destination. 
     However, an IP frame solves this problem because the removal of the MAC addresses therefrom means that it is no longer subject to the size limitations of the Ethernet protocol. As a result, large IP packets need not be fragmented by a gateway (intermediate router) to a LAN and can be transported in their entirety to a destination without being dropped by intermediate routers. 
     H.3 Enabling Layer 2 Redundancy 
     Nowadays, layer 2 redundancy is designed in an active/backup link architecture. Referring to  FIG. 14 , a looped LAN switch comprises three LAN switches S 1 , S 2  and S 3 , wherein switches S 1  and S 3  are respectively connected to hosts H 1  and H 2 . Switch S 1  is connected to switches S 2  and S 3  by lines L 12  and L 13  respectively. Similarly, switch S 2  is connected switch S 3  by line L 23 . With this arrangement (which is also known as an L 2  loop), even if switch S 2  fails, hosts H 1  and H 2  can still communicate through switches S 1  and S 3  via line L 13 . Thus, there is a first active link L 13  and an inactive link L 23  to switch S 3 . 
     However, the looped LAN switch arrangement can give rise to problems with unicast flooding. For example, let host H 1  attempt to communicate with host H 2 . Further, let host H 1  be unaware of the MAC address of host H 2 . The switch S 1  issues a packet through all of its ports (apart from the one connected to host H 1 ). The packet travels through lines L 12  or L 13  to switches S 2  and S 3 . Switches S 2  and S 3  will incorrectly associate the MAC address of host H 1  with their ports connected to lines L 12  or L 13  and in accordance with the normal dynamic learning procedure will add the MAC address of host H 1  to their MAC tables. If neither switch has learned the MAC address for host H 2  yet, they will unicast flood onto line L 23 . Each switch will take the packet sent by the other switch and flood it back out again immediately, since they still don&#39;t know the MAC address of host H 2 . The unicast packets will continue to be transmitted around the loop until the host H 2  replies whereupon its MAC address will be added to the switch&#39;s MAC address table and the unicast flooding will stop. 
     However, a much more serious problem arises with broadcast storms, wherein broadcast packets are broadcast, received and rebroadcast by each switch, so that the broadcast packets never leave (or stop travelling around) the loop. The increased traffic resulting from the never-ending broadcast and rebroadcast of these packets leads to traffic congestion and misconnections on the Internet. It will be understood that broadcast storms can also occur in redundant links between a single switch and a single host. 
     The spanning tree protocol overcomes unicast flooding loops and broadcast loops by breaking such loops. However, the spanning tree protocol takes about 50 seconds to perform such topology changes. A more recent protocol, namely the rapid spanning tree protocol takes only 1-2 seconds to perform such topology changes. Nevertheless, in many applications (e.g. voice over IP or video streaming) a 1-2 second delay is unacceptable. 
     The IP frame and IP switch overcomes the problems of broadcast storms by suppressing L 2  loops between improved IP routers, insofar as frames are natively transported without Ethernet encapsulation. In particular, only the preamble and CRC fields are conserved from an Ethernet frame. The resulting IP packets are directly switched by the IP switch on the basis of the IP destination addresses in the IP header field of the IP frame. In particular, the IP switch no longer uses MAC addresses to switch frames to an appropriate port. Thus, instead of performing a full broadcast (of a LAN switch), the IP switch performs a directed broadcast to all its IP peers with the IP address contained in the direct broadcast subnetwork. Similarly, instead of the aforementioned L2 active main link and inactive L2 backup link between a host and a conventional LAN switch, the IP switch permits the use of multiple active L3 links to a host. This feature enables load-balancing between routers, wherein this option would not otherwise have been available with a conventional LAN switch. 
     H.4 Enabling Layer 3 Redundancy 
     Referring to  FIG. 15 , to eliminate a single point of failure for clients on a network accessing the Internet, a network administrator might consider deploying two routers, R 1  and R 2  connected through a switch S to a one or more hosts H 1 -H n . The TCP/IP settings of the hosts will have been configured with the IP address of a default gateway (router R 1 ). However, if router R 1  fails, a host H 1  will be left with a default gateway at an unreachable IP address. Similarly, if the host uses ARP to resolve the IP address of the default gateway to its MAC address, then even if the hardware of router R 1  is replaced, the host will still not have access to the Internet until its ARP cache has timed out or cleared. 
     The Virtual Router Redundancy Protocol (VRRP) is designed to guard against such failures, and to provide faster and more efficient failover in the event of an outage than traditional dynamic routing techniques. When VRRP is started, it provides a master router with a virtual media access control (VMAC) address, which is taken over by another router (i.e. a backup router) in the event of failover. By employing a virtual MAC address, network hosts need not change their default-gateway address in the event of failover. Thus, in effect, this system employs an L2 link between a host H 1  and switch S and an active and inactive L2 links between the switch S and routers R 1  and R 2  (to support the VRRP). One of the limitations of this approach is that standby routers are idle until a master router fails. 
     By not using MAC addresses, the IP switch enables the above-described redundant router structure to be modified. In particular, the conventional routers R 1  and R 2  are replaced by IP switches and a host directly connected thereto (by removing the interceding LAN switch) by multiple active L3 links. The availability of the multiple active L3 links between a host and an IP switch means that a backup IP router need not be dormant while the master router is active. Instead, both IP switches can be active at the same time, thereby enabling load-sharing therebetween. 
     Similarly, the IP switch no longer needs to use the spanning tree protocol to remove L 2  loops. Instead, the IP switch need only rely on dynamic IP routing protocols (e.g. OSPF) to identify the best next loop (route) for the IP frame to transmit it to its intended destination. This ensures that the convergence time of the IP switch is improved from 1-2 seconds (with the spanning tree protocol) to 200 ms (with OSPF), wherein this delay time is acceptable for real-time, delay-sensitive traffic such as voice over IP. 
     In addition, the IP switch and IP frame enable the replacement of active and inactive links with completely active links, thereby facilitating load-balancing (in a fashion similar to ECMP which is already provided under OSPF). 
     I. Other Features 
     In common with the IP switch, the Network Interface Cards (NIC) in hosts no longer transmit traditional Ethernet packets. Instead, with the IP frame, the NICs forward IP packets natively on the wire. The IP default gateway should be the directly attached IP switch. However, this is not essential. In particular, an IP default gateway is no longer required when there is only one NIC per host if a pair of NICs is used in redundancy mode. Thus, an IP default gateway is no longer needed and both NICs can be used in an active/active fashion, thereby providing the facility for load-sharing. In other words, the existing limitations of using active/backup links when using two NICs on an end-server no longer apply. 
     Furthermore, while a full duplex environment is still required on a LAN to transmit the improved frame. CSMA/CD is no longer needed. Neither the IP frame, nor the IP switch modify traditional IP multicast mechanisms. Indeed, general multicast mechanisms are simplified since IGMP snooping or CGMP are no longer required. The present invention provides a computer program product stored in a medium readable by a computer, the computer program product tangibly embodying readable program means for causing the computer to perform the methods of the present invention. Thus, the computer program product comprises a storage medium having computer readable program code (i.e., the readable program means) stored therein, said program code configured to be executed by a computer to cause the computer to perform the methods of the present invention. 
     The present invention provides a system comprising means for carrying out the methods of the present invention. The system comprises a computer configured to execute program code stored in a storage medium to perform the methods of the present invention. 
     While particular embodiments of the present invention have been described herein for purposes of illustration, many modifications and changes will become apparent to those skilled in the art. Accordingly, the appended claims are intended to encompass all such modifications and changes as fall within the true spirit and scope of this invention.