Abstract:
An apparatus provides a hardware-based solution to enable support for L3 switching, network address port translation and application level gateways. The architecture involved in this hardware approach is such that it is scalable for implementation in a variety networking products that fulfill enterprise security and all possible combinations of wired and wireless networking needs, such as access points, access point concentrators, wireless-ready wiring closet or edge switches, and wireless co-processors.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application claims priority to provisional application 60/484,811, filed on Jul. 3, 2003. 
     
    
     FIELD OF THE INVENTION  
       [0002]     Aspects of the present invention relate generally to network communications, and more particularly, to wired and wireless networks and architectures.  
       BACKGROUND  
       [0003]     The Wireless Local Area Network (WLAN) market has recently experienced rapid growth, primarily driven by consumer demand for home networking. The next phase of the growth will likely come from the commercial segment, such as enterprises, service provider networks in public places (Hotspots), multi-tenant, multi-dwelling units (MxUs) and small office home office (SOHOs). The worldwide market for the commercial segment is expected to grow from 5M units in 2001 to over 33M units in 2006. However, this growth can be realized only if the issues of security, service quality and user experience are addressed effectively in newer products.  
         [0004]      FIG. 1  illustrates possible wireless network topologies. As shown in  FIG. 1 , a wireless network  100  typically includes at least one access point  102 , to which wireless-capable devices such as desktop computers, laptop computers, PDAs, cellphones, etc. can connect via wireless protocols such as 802.11a/b/g. Several or more access points  102  can be further connected to an access point controller  104 . Switch  106  can be connected to multiple access points  102 , access point controllers  104 , or other wired and/or wireless network elements such as switches, bridges, computers, and servers. Switch  106  can further provide an uplink to another network. Many possible alternative topologies are possible, and this figure is intended to illuminate, rather than limit, the present inventions.  
         [0005]     One important issue with respect to wireless networking is the problem of Roaming and Session Persistence. Roaming allows the user to move from one network to another. (across same networks or across subnets) The user may do this intentionally to utilize a better or faster connection through a different Access Point or because user location has changed. Assuming that the user is originally authenticated while roaming user authentication across a WLAN should be transparent. The user should not require any manual action or any special application. There should be no reconfiguration needed when the user changes from one subnet to another. Any reconfiguration necessary should be done automatically. When roaming across subnets the WLAN user will encounter a problem with DHCP. As client changes network the new DHCP-server will provide a new IP-address. This will result in a break in an ongoing connection/session.  
         [0006]     “Session persistence” means more than forwarding packets to a user&#39;s new location. “Persistence” can refer to just the problem of having packets forwarded as users roam among subnets, coverage areas and network types (wired LANs, wireless LANs and wireless WANs). More generally, it should refer to transport and application session persistence because when a transport protocol cannot communicate to its peer, the underlying protocols, like TCP, assume that the disruption of service is due to network congestion. When this occurs these protocols back off, reducing performance and eventually terminating the connection. WLAN networks have coverage holes causing dropouts even with access point overlap. This impacts a mobile device&#39;s range of mobility.  
         [0007]     Meanwhile, many WLAN vendors are integrating combined 802.11a/g/b standards into their chipsets. Such chipsets are targeted for what are called Combo-Access Points which will allow users associated with the Access Points to share 100 Mbits of bandwidth in Normal Mode and up to ˜300 Mbits in Turbo Mode. The table below shows why a software roaming solution without hardware acceleration is not feasible when bandwidth/speeds exceed 100 Mbits.  
                                                                                                           Required                       Processor Speed           Interface       [MHz]   CPU                BW       IPSec +   Subsys       Type   [Mbs]   IPSec   Other   Cost               DSL   1-5    133    200+           Ether    10    300    500+       802.11a   30-50   1200   1500+   $400                       [2002]                       $125                       [2004]       Fast    100   2500   3000+   $600       Ether               [2002]                       $250                       [2004]            Multiple    500   Not Feasible in Software           FE       Needs Dedicated Hardware       Gigabit   1000       Ether                  
 
         [0008]     Although infrastructures for wired networks have been highly developed, the above and other problems of wireless networks are comparatively less addressed. Meanwhile, there is a need to address situations where enterprises and/or networks may have any combination of both wired and wireless components.  
         [0009]     Further, another important feature for network devices that is not implemented in hardware, thus adversely affecting both wired and wireless network throughput, is support for L3 switching, network address port translation (NAPT) and application level gateways (ALGs).  
       SUMMARY  
       [0010]     Aspects of the present invention relate generally to a single-chip solution that addresses current weaknesses in wireless networks, but yet is scalable for a multitude of possible wired and/or wireless implementations. Current solutions to resolve/overcome the weaknesses of WLAN are only available in the form of Software or System. These resolve only specific WLAN problems and they don&#39;t address all of the existing limitations of wireless networks.  
         [0011]     In accordance with an aspect of the invention, an apparatus provides a hardware-based solution to enable support for L3 switching, network address port translation and application level gateways. The architecture involved in this hardware approach is such that it is scalable for implementation in a variety networking products that fulfill enterprise security and all possible combinations of wired and wireless networking needs, such as access points, access point concentrators, wireless-ready wiring closet or edge switches, and wireless co-processors. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     These and other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures, wherein:  
         [0013]      FIG. 1  illustrates wireless network topologies;  
         [0014]      FIG. 2  is a block diagram illustrating a wired and wireless network device architecture in accordance with an embodiment of the present invention; and  
         [0015]      FIG. 3  is a block diagram illustrating operation of a NAPT protocol embodiment. 
     
    
     DETAILED DESCRIPTION  
       [0016]     One aspect of the present invention is the discovery that a hardware network device and solution may address wired and wireless network performance, including support for L3 switching, NAPT and ALGs. Such a device and solution may also be scalable to enable implementation in the various components and alternative topologies of wired and/or wireless networks, such as, for example, in an access point, an access point controller, or in a switch.  
         [0017]     The embodiments of the present invention will now be described in detail with reference to the drawings, which are provided as illustrative examples of the invention so as to enable those skilled in the art to practice various embodiments of the invention. Notably, the figures and examples below are not meant to limit the scope of the present invention. Moreover, where certain elements of the embodiments can be partially or fully implemented using known components, only those portions of such known components that are necessary for an understanding of the embodiment will be described, and detailed descriptions of other portions of such known components will be omitted so as not to obscure the invention. Still further, the present invention encompasses present and future known equivalents to the known components referred to herein by way of illustration, and implementations including such equivalents are to be considered alternative embodiments of the invention.  
         [0018]      FIG. 2  is a block diagram illustrating an example of a single-chip wired and wireless network device  200  that can implement integrated hardware support for L3 switching, network address port translation, and application level gateways according to the present invention. As shown in  FIG. 2 , chip  200  includes ingress logic  202 , packet memory and control  204 , egress logic  206 , crypto engine  208 , an embedded processor engine  210  and an aggregator  212 . Co-pending application No. ______ (Atty. Dkt. 79202-309844; SNT-001) describes the device  200  in more detail and its contents are incorporated herein by reference.  
         [0019]     In one example implementation of the present invention, L3 switching, network address port translation, and application level gateways are supported by hardware in the ingress and egress paths  202  and  206 , as well as by firmware running on the embedded processor engine  210 .  
         [0020]     As is known, Network Address Translation (NAT) is a method by which IP Addresses are mapped from one addressing realm to another, providing transparent routing to end hosts. Traditionally, NAT is used to connect an isolated addressing realm with private unregistered addresses to an external addressing realm with globally registered addresses. Network Address Port Translation (NAPT) extends the notion of translation one step further by also translating the transport identifiers (e.g., TCP/UDP port numbers, ICMP query identifiers). This allows the transport identifiers of multiple private hosts to be multiplexed onto the transport identifiers of a single external address. NAPT allows a set of hosts to share a single IP address or a small number of IP addresses. For packets outbound from the private network, NAPT would translate the source IP address, source transport identifier like the TCP/UDP port or ICMP query identifier, and related fields like the IP header checksum and the TCP/UDP/ICMP header checksum. For inbound packets, the destination IP address, destination transport identifier and the IP and transport header checksums would be modified.  
         [0021]      FIG. 3  illustrates mapping of IP address and port using the NAPT functionality between the wireless station A and the destination B. DA and SA stand for Destination Address-Port pair and Source Address-Port pair respectively. The tuple (A,a) denotes (IP Address=A, Port=a). As shown in  FIG. 3 , a wireless station A, that is associated with an AP labeled X, communicating with a destination B over a TCP or UDP connection. Let DA denote the (Destination IP Address, Destination Port) tuple while SA will denote the (Source IP Address, Source Port) tuple. When station A, with IP Address A, sets up a connection between its own Port a and Port b on destination B with an IP Address B, the outbound session from station A, as shown in the figure, uses DA=(B,b) and SA=(A,a). The NAPT function on the AP alters the SA used to (X,x). The destination B is only aware of a connection with DA=(B,b) and SA=(X,x) and so it sets up a return connection with DA=(X,x) and SA=(B,b). The NAPT function on the AP uses the reverse mapping to remap this connection to one with DA=(A,a) and SA=(B,b), there by enabling a bi-directional connection to be set up. This bi-directional address binding is stored in the AP and used to translate packets between station A and destination B. The AP alters the SA on every packet from the station A to destination B using the (A,a)-&gt;(X,x) mapping while in the reverse direction it uses the (X,x)-&gt;(A,a) mapping to alter the DA on the packets going from the server B to station A. Note that packets exchanged between two wireless stations do not need NAPT support, and the same holds for packets exchanged between two hosts on the wired domain.  
         [0022]     According to the present invention, integrated L3 switching, NAPT and ALG functionality on the device  200  is supported using a unified NAT/Encapsulation Table. One entry is created per direction per connection. In one example, the Table in device  200  will have (2K*2)=4K entries, thereby supporting 2K connections.  
                                                                                 Size   Default       Field   Description   Name   (bits)   Value                                Destination   Index to the location in the ARP Table of the   Dst_IP_Index   13   0       IP Index   Destination IP address in the Header       Source IP   Index to the location in the ARP Table of the   Src_IP_Index   13   0       Index   Source IP address in the Header       Destination   Destination port in the TCP/UDP Header   Dest_Port   16   0       Port       Source Port   Source port in the TCP/UDP Header   Src_Port   16   0       Protocol   Indicates the Transport Protocol for the   Protocol   1   0           entry. Logic 0 indicates UDP while logic 1           indicates TCP.       New IP   Index to the location in the ARP Table of the   New_IP_Index   13   0       Index   IP Address for NAT or Tunnel       New Port   Port for NAT or Tunnel   New_Port   16   0       Operation   Logic 0 indicates swapping fields while logic   Op   1   0           1 indicates encapsulation.       EpeSelect   This bit is set to logic 1 if the packet needs to   EpeSelect   1   0           be sent to the Embedded Processing Engine           (EPE).       EpeNum   Logic 0 indicates EPE0 and logic 1 indicates   EpeNum   1   0           EPE 1.       Age   This field is used to indicate validity and also   Age   2   0           age. 0x3 indicates invalid while the other           values indicate age.                  
 
         [0023]     The Host CPU sets up the entries in the NAT/Encapsulation Table. Setting the Age field to logic 0×3 indicates an invalid entry; other values are used to indicate various levels of age. For the NAPT functionality, the Operation field should have the value 0. A hash-based lookup of this table is uses a key comprising (Dest_IP_Index, Src_IP_Index, Dest_Port, Src_Port, Protocol) and returns (New_IP_Index, New_Port, Operation, EpeSelect, EpeNum). Every time an entry is accessed in the table the Age field is reset. A timer is used to periodically increase the age of the entry.  
         [0024]     For a TCP connection, the first packet with the SYN bit set indicates the start of a connection, while a packet with the FIN bit or RST set indicates the end of a connection. If a packet arrives with a SYN bit set (for TCP) or if a lookup fails (for TCP or UDP), the packet is sent to the Host CPU, which then proceeds to set up an entry indicating the address binding for the connection in the NAT/Encapsulation Table. If a TCP packet arrives with the FIN bit or RST bit set, the corresponding entry is deleted from the table. Note that the Host CPU must wait for TCP_TIME_WAIT period of 4 min before assigning the same address binding to another connection. Alternatively, if a new connection is needed and the NAT/Encapsulation Table is full, an LRU policy is used to replace the existing connections.  
         [0025]     The NAT/Encapsulation Table lookup is preceded by two lookups of the ARP table—one based on the Source IP Address and one based on the Destination IP Address. These are primarily to obtain the indices corresponding to the locations of the Source IP Address and the Destination IP Address in the ARP Table. The NAT Table stores these indices instead of the actual 32-bit addresses to reduce the size of the table. The NAT Table lookup returns a New_IP_Index and a New_Port. However, in the “Wireless-to-Wired” direction, the New_IP_Index and New_Port values are not used to replace the (Src_IP, Src_Port) pair in the packet header immediately. This is because the inbound ACL processing is done using the original (Src_IP, Src_Port) value. In the “Wired-to-Wireless” direction, the New_IP_Index and New_Port values are used to replace the (Dst_IP, Dst_Port) pair right away and the new Destination IP Address is used to perform the lookup in the ARP Table as well as the inbound ACL processing. The IP Header and TCP/UDP Header Checksums need to be updated following the change.  
         [0026]     Some packets need to be sent to the Embedded Processor Engine (EPE) where all the ALGs are to be executed. After the ALGs have been used to update the packet fields, the packet is reintroduced into the packet pipeline. Note that not all packets need to be sent to the EPE. For example, in an FTP session, only the packets from the FTP Control session are sent to the EPE. The FTP ALG running on the EPE maintains a table for where it stores the (Delta_Seq, Delta_Ack) for each direction of each FTP connection. (Delta_Seq, Delta_Ack) are the differences from the original sequence and acknowledgement numbers respectively caused by the modifications to the IP Address and Port carried in the payload of the PORT command and PASV response. Every PORT command and PASV response results in an update to the (Delta_Seq, Delta_Ack) values. Every subsequent control packet, that is not PORT or PASV, has its sequence number and acknowledgement number updated using the (Delta_Seq, Delta_Ack) values.  
         [0027]     The Known Ports Table is used to check if the Source or Destination TCP/UDP ports correspond to ports that require ALG processing. The Known Ports Table has a list of well known ports that are used to set up connections for various applications like FTP, SIP, H.323 etc. In some applications, the later stages of the connection set up usually involve negotiation of ephemeral ports. To trap packets headed to these ports and send them to the EPE, the EPE makes the appropriate entry in the NAT/Encapsulation Table and also sets the NatEn bit for the corresponding IP Address in the ARP Table. Any Wireless-to-Wired packet always performed a NAT/Encapsulation Table lookup. All other packets perform the lookup only if the entry corresponding to the Destination IP Address in the ARP Table has the NatEn bit set.  
         [0028]     Although the present invention has been particularly described with reference to the preferred embodiments thereof, it should be readily apparent to those of ordinary skill in the art that changes and modifications in the form and details may be made without departing from the spirit and scope of the invention. It is intended that the appended claims include such changes and modifications.