Abstract:
Methods and apparatus for enabling a layer 2 node associated with an open systems interconnection (OSI) reference model to perform resource reservation protocol (RSVP) processing are disclosed. According to one aspect of the present invention a layer 2 device associated with an OSI reference model includes a first interface, a processing arrangement, and a second interface. The first interface intercepts a message associated with a on-path signaling protocol for at least one selected from a group including resource reservation and admission control at a layer above layer 2. The processing arrangement processes the message, and the second interface sends the message.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    The present invention relates generally to internet protocol (IP) signaling in networks. More particularly, the present invention relates to extending a resource reservation protocol for use in enabling on-path admission control at Ethernet switching hops located between IP hops. 
         [0003]    2. Description of the Related Art 
         [0004]    An on-path Internet Protocol (IP) reservation protocol is a reservation protocol in which reservation messages and reservation state are established and maintained along the path between an IP sender and IP receiver. One example of an on-path IP reservation protocol, or an on-path signaling protocol, is a resource reservation protocol (RSVP). RSVP is used in networks that enable Internet applications to obtain quality of service for their traffic. RSVP, while not a routing protocol, works in conjunction with routing protocols such as unicast and multicast routing protocols. RSVP effectively carries a request through elements of a network, and attempts to make a resource reservation at each appropriate element in order to achieve a particular quality of service end to end. 
         [0005]    To attempt to make a resource reservation at a network element, e.g., at a router or a server, in response to a resource reservation request, an RSVP daemon of the network element may communicate with an admission control module of the network element. The admission control module generally ascertains whether the network element is able to accommodate the resource reservation request, i.e., whether the network element is able to provide the requested quality of service. If the network element does not have sufficient resources to provide the requested quality of service, an error notification is sent to the application that initiated the resource reservation request. Otherwise, a resource reservation is made at the network element. 
         [0006]    Typically, a resource reservation request begins with a path (PATH) message being sent from a sender or a source to a receiver or a destination. After receiving the PATH message, the receiver sends a reservation (RESV) message back to the sender. The network elements traversed by the PATH message and the RESV message may include IP capable network elements, e.g., layer 3 elements with respect to the Open Systems Interconnection (OSI) reference model specification which may thus be RSVP capable, and network elements that are not IP capable, e.g., layer 2 elements with respect to the OSI reference model specification such as Ethernet switches, which therefore are not RSVP capable. It should be appreciated that some layer 3 elements are also not RSVP capable. 
         [0007]      FIG. 1  is a block diagram representation of a network with IP-capable network elements and a non IP-capable Ethernet switch, in which a resource reservation is to be made. In a network  100 , a sender  104  that has a sender or source IP address of IP 13    0  sends a PATH message  122  towards a receiver  118 . PATH message  122  includes the sender IP address of IP_ 0  and a receiver IP address of IP_ 3 . Before PATH message  122  reaches receiver  118 , PATH message  122  passes through RSVP capable routers  106 ,  114  and an Ethernet switch  110 , which is not IP capable and (hence) not RSVP capable. Assuming that PATH message  122  reaches receiver  118 , receiver  118  originates a RESV message  126  that traverses RSVP capable routers  114 ,  108  and Ethernet switch  110  en route to sender  104 . Routers  114 ,  108  each have IP and media access control (MAC) addresses, and are arranged to reserve resources in response to RESV message  126 . 
         [0008]    With reference to  FIG. 2A , one method of attempting to establish path states prior to reserving resources in network  100  of  FIG. 1  by sending a PATH message will be described. A process  200  of initiating the reservation of resources in network  100  of  FIG. 1  using a PATH message begins at step  202  in which a sender sends a PATH message towards a receiver. The PATH message specifies an IP address associated with the sender, as for example an IP address of IP_ 0 , and an IP address associated with the receiver, as for example an IP address of IP_ 3 . The PATH message also specifies an IP address indicating the RSVP hop, as for example an IP address of IP_ 0  since the sender is the first RSVP hop. In step  204 , a first router receives the PATH message and processes the PATH message as an RSVP message. Typically, when the first router identifies a Router Alert option in the IP header and identifies IP protocol number 46 in the PATH message, the first router initiates RSVP processing. RSVP processing of the PATH message includes updating the IP address of the RSVP hop, which in this case is set by the first router to IP_ 1 . RSVP processing may include using a routing table to determine a layer 3 next hop and, hence, an outbound interface for the PATH message. As shown in  FIG. 1 , the next layer 3 hop towards the receiver is a second router with a MAC address of MAC_ 2 . Hence, the first router sets a specified source MAC address in the Ethernet Header of the frame carrying the PATH message to its own MAC address, i.e., MAC_ 1 , and sets a specified destination MAC address in the Ethernet header of the frame carrying the PATH message to MAC_ 2 . 
         [0009]    As will be appreciated by those skilled in the art, errors may occur during RSVP processing. By way of example, an error may occur if the first router effectively has no route or path to the receiver. Hence, in step  206 , it is determined if an error has arisen during RSVP processing. If it is determined that an error has arisen, a path error (PATH_ERR) message is returned to the sender in step  207 , and the process of reserving resources is terminated. 
         [0010]    Alternatively, if the determination in step  206  is that no error has occurred during RSVP processing, the process flow proceeds to step  208  in which the first router forwards the path message to the Ethernet switch in the path between the first router and the second router. The routing table of the first router is used to identify the interface towards the Ethernet switch as being in the path towards the second router. The Ethernet switch is not an IP capable device and, as a result, is not even aware that the Ethernet frame actually carries an RSVP message. Thus, the Ethernet switch performs no RSVP processing and forwards the PATH message using the specified MAC addresses inside the Ethernet Header. Conventional rules of bridging are generally used by the Ethernet switch to forward the Ethernet frame which carries the PATH message using the MAC addresses to the second router in step  210 . As will be appreciated by those skilled in the art, the Ethernet switch does not update any addresses specified in the PATH message. 
         [0011]    On receipt of the PATH message, the second router will notice that its IP Header contains the Router Alert option and has an IP protocol number of 46 and hence initiate RSVP processing. The second router processes the path message in step  212  and uses a routing table to determine a layer 3 next hop. The second router also updates the IP address on the RSVP hop and sets it to IP_ 2 . A determination is made in step  214  as to whether an error has arisen during RSVP processing. If it is determined that an error has arisen, a PATH_ERR message is returned towards the sender in step  214 . When the second router returns the PATH_ERR message, the PATH_ERR message is returned with a source MAC address of the second router and a destination MAC address of the first router. Once the error message is returned to the sender, the process of establishing path states is terminated. 
         [0012]    Returning to step  214 , if it is determined that no error has arisen during RSVP processing, the indication is that the PATH message may be forwarded by the second router further towards its receiver. As such, the second router forwards the PATH message in step  216  to the receiver using the routing table of the second router to identify the path to the receiver. After the PATH message is forwarded to the receiver, the process of establishing path state end to end is completed. Note that each RSVP hop now knows the previous RSVP hop from the sender to the receiver. 
         [0013]    When a PATH message is successfully received at a receiver, the receiver can send a RESV message back towards the sender of the PATH message to reserve resources. To ensure that the RESV message is sent along the same path used by the PATH message, the RESV message is routed hop-to-hop using path state information, including a previous RSVP hop, that was effectively set up during the processing of the PATH message.  FIG. 2B  is a process flow diagram which illustrates steps associated with processing a RESV message in network  100  of  FIG. 1 . A process  230  of reserving resources using a RESV message begins at step  232  in which a receiver sends a RESV message towards a sender with destination and source IP addresses specified. That is, the RESV message is sent by the receiver with a source IP address of IP_ 3 , as receiver  118  of  FIG. 1  is the source of the RESV message, and a destination IP address of IP_ 2 , as second router  114  of  FIG. 1  is the previous RSVP hop on the path from the sender to the receiver. 
         [0014]    After being sent towards the sender, the RESV message is received and processed as an RSVP message in step  234  by the second router. The second router, i.e., router  114  of  FIG. 1 , identifies the RESV message as being an RSVP message. Path state information set up by the path message will be used by the first router to identify the next hop to which to forward the RESV message. A determination is made in step  236  as to whether there is an error in RSVP processing. An error may arise, for example, if there is an admission control failure relative to the second router. If it is determined that an error has arisen during RSVP processing by the second router, the second router returns a RESV error (RESV_ERR) message to the receiver, i.e., the originator of the RESV message, in step  237 , and the processing of a RESV message is completed. The RESV_ERR message is returned with a source IP address set as the IP address of the second router, namely IP address IP_ 2 , and a destination IP address set as the IP address of the RSVP next hop, namely IP address IP_ 3 . 
         [0015]    Alternatively, if it is determined in step  236  that there has been no error in RSVP processing, the second router forwards the RESV message to the Ethernet switch that is in the path between the second router and the first router. The second router generates the RESV message with a source addresses set to an address of the second router, and with a destination address set to an address of the first router. Upon receiving the RESV message, the Ethernet switch forwards the RESV message to the first router using MAC addresses in step  240 . As the Ethernet switch is not an RSVP capable device, the Ethernet switch uses layer 2 address information to determine how to forward the RESV message. The Ethernet switch does not update addresses in the RESV message. 
         [0016]    Once the Ethernet switch forwards the RESV message to the first router, the first router processes the RESV message as an RSVP message in step  242 . Path state information set up by the path message will be used by the first router to identify the next hop to which to forward the RESV message. It is determined in step  244  whether an error has occurred in the course of RSVP processing. If it is determined that an error has occurred, then the first router returns a RESV_ERR message to the receiver in step  245 . The RESV_ERR message is sent by the first router to the receiver with a source IP address of the RESV_ERR message set as the IP address of the first router, i.e., IP address IP_ 1 , and with the destination IP address of the RESV_ERR message set as the IP address of the next RSVP hop, i.e., IP address IP_ 2 . After the RESV_ERR message is sent, the processing of a RESV message is completed. 
         [0017]    Returning to step  244 , if it is determined that RSVP processing by the first router has not resulted in an error, then the first router forwards the RESV message to the sender using its routing table to identify a suitable outbound interface in step  246 . Once the RESV message is forwarded to the sender, the processing of a RESV message is successfully completed. 
         [0018]    Ethernet switches are not capable of providing admission control capabilities. In other words, Ethernet does not provide native admission control functionality available relative to layer 2 devices or layer 2 networks. Hence, though a path may effectively be reserved, if that path passes through an Ethernet switch or an Ethernet network, traffic sent on the reserved path may encounter congestion due to insufficient capacity when the traffic reaches the Ethernet switch or the Ethernet network. 
         [0019]    To provide some admission control capabilities for layer 2 devices, an RSVP subnet bandwidth manager (SBM) may be implemented on each layer 2 device and on each edge device, or device on the edges of a layer 2 device or a layer 2 network. SBM is an extension of the RSVP protocol that enables on-path admission control at Ethernet hops located between IP hops, and is specified in RFC2814, which is incorporated herein by reference. Referring again to  FIG. 1 , Ethernet switch  110  may be an Ethernet hop that includes a SBM and a MAC layer agent, and routers  106 ,  114  may be IP hops that include SBM clients. 
         [0020]    To implement SBM, an Ethernet hop inserts itself as an RSVP hop in the signaling path. This generally requires that the Ethernet hop implements an IP host functionality which includes having IP reachability into the layer 2 cloud and being allocated an IP address in this layer 2 cloud. Moreover, where multiple virtual local area networks (VLANs) are used in a layer 2 domain, the use of SBM to achieve admission control in substantially all the VLANs would generally require that the Ethernet hop implements an IP host functionality in each VLAN, and utilizes one separate IP address in each VLAN. Implementing such IP host functionality typically results in a more complicated implementation relative to an Ethernet hop, requires significant administration, and impacts scalability. Thus, providing admission control over an Ethernet hop via SBM may be inefficient. 
         [0021]    Therefore, what is needed is a system that allows RSVP to be extended such that layer 2 devices may provide on-path signaling control without supporting IP forwarding functionality. That is, what is desired is a method and an apparatus for efficiently providing admission control capabilities for layer 2 devices. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The invention may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which: 
           [0023]      FIG. 1  is a block diagram representation of a network with resource reservation protocol (RSVP) capable network elements and an Ethernet switch, in which a resource reservation is to be made. 
           [0024]      FIG. 2A  is a process flow diagram which illustrates a method of processing a path (PATH) message. 
           [0025]      FIG. 2B  is a process flow diagram which illustrates a method of processing a reservation (RESV) message. 
           [0026]      FIG. 3A  is a block diagram representation of a layer 2 network element which is capable of processing RSVP packets in accordance with an embodiment of the present invention. 
           [0027]      FIG. 3B  is a diagrammatic representation of a RSVP packet, e.g., RSVP packet  304  of  FIG. 3A . 
           [0028]      FIG. 4A  is a diagrammatic representation of a network with RSVP capable network elements and an Ethernet aggregation network in which a resource reservation is to be made. 
           [0029]      FIG. 4B  is a diagrammatic representation of layer 2 agents in an Ethernet aggregation network, e.g., Ethernet aggregation network  412  of  FIG. 4A , that are arranged to use RSVP information for on-path signaling in accordance with an embodiment of the present invention. 
           [0030]      FIG. 4C  is a diagrammatic representation of a RSVP capable node, e.g., node ‘1’  406  of  FIG. 4A , performing an address resolution protocol (ARP) message to update (media access control) MAC address tables in layer 2 agents of an Ethernet aggregation network e.g., Ethernet aggregation network  412  of  FIG. 4A , in accordance with an embodiment of the present invention. 
           [0031]      FIGS. 5A-5C  are a process flow diagram which illustrates one method of processing a PATH message in a network with layer 2 agents that are arranged to use RSVP information for on-path signaling in accordance with an embodiment of the present invention. 
           [0032]      FIG. 6A  is a process flow diagram which illustrates a first method of performing error processing in response to a PATH message at a layer 2 agent that is arranged to use RSVP information for on-path signaling, i.e., step  515  of  FIG. 5A , in accordance with an embodiment of the present invention. 
           [0033]      FIG. 6B  is a process flow diagram which illustrates a second method of performing error processing in response to a PATH message at a layer 2 agent that is arranged to use RSVP information for on-path signaling, i.e., step  515  of  FIG. 5A , in accordance with an embodiment of the present invention. 
           [0034]      FIG. 6C  is a process flow diagram which illustrates a third method of performing error processing in response to a PATH message at a layer 2 agent that is arranged to use RSVP information for on-path signaling, i.e., step  515  of  FIG. 5A , in accordance with an embodiment of the present invention. 
           [0035]      FIGS. 7A-7C  are a process flow diagram which illustrates one method of processing a RESV message in a network with layer 2 agents that are arranged to use RSVP information for on-path signaling in accordance with an embodiment of the present invention. 
           [0036]      FIG. 8A  is a process flow diagram which illustrates a first method of performing error processing in response to a RESV message at a layer 2 agent that is arranged to use RSVP information for on-path signaling, i.e., step  715  of  FIG. 7A , in accordance with an embodiment of the present invention. 
           [0037]      FIG. 8B  is a process flow diagram which illustrates a second method of performing error processing in response to a RESV message at a layer 2 agent that is arranged to use RSVP information for on-path signaling, i.e., step  715  of  FIG. 7A , in accordance with an embodiment of the present invention. 
           [0038]      FIG. 8C  is a process flow diagram which illustrates a third method of performing error processing in response to a RESV message at a layer 2 agent that is arranged to use RSVP information for on-path signaling, i.e., step  715  of  FIG. 7A , in accordance with an embodiment of the present invention. 
           [0039]      FIG. 8D  is a process flow diagram which illustrates a fourth method of performing error processing in response to a RESV message at a layer 2 agent that is arranged to use RSVP information for on-path signaling, i.e., step  715  of  FIG. 7A , in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0040]    Providing on-path signaling and on-path admission control for devices at layer 2 of an Open Systems Interconnection (OSI) reference model would increase the efficiency with which an overall network may operate. Providing on-path admission control and, hence, reserving resources associated with a layer 2 device, e.g., an Ethernet switch, that is located in a path between layer 3 hops of device, e.g., internet protocol (IP) routers, increases the Quality of Service (QoS) provided by a network. A network with layer 2 devices that provide on-path signaling and on-path admission control may provide substantially increased bandwidth efficiency in suitable networks such as enterprise or service provider networks that support voice or video applications. 
         [0041]    In one embodiment, on-path signaling and on-path admission control is provided through an on-path IP reservation protocol such as a resource reservation protocol (RSVP). Although RSVP is described, it should be understood that RSVP is just one example of an on-path IP reservation protocol. If a protocol such as RSVP may be supported by layer 2 devices or in layer 2 networks such as Ethernet networks substantially without requiring IP forwarding functionality in the layer 2 devices or in layer 2 networks, the implementation and administration of the layer 2 devices or the layer 2 network may be relatively uncomplicated as well as more scaleable. Allowing RSVP to be supported for on-path signaling in a layer 2 environment extends the ability to reserve resources in an overall network. More generally, allowing substantially any on-path IP reservation protocol to be supported for on-path signaling in a layer 2 environment allows for the extended ability to reserve resources. 
         [0042]    Generally, routing at an IP level may be either asymmetric or symmetric. Forwarding in a layer 2 network may be based on a bridge learning algorithm combined with the Spanning Tree Protocol (STP). The bridge learning algorithm uses a source media access control (MAC) address of an Ethernet frame arriving at an interface to determine which interface a frame with the same destination MAC address may be forwarded on. As will be appreciated by those skilled in the art, the Spanning Tree Protocol is used in switched networks to prevent forwarding loops. That is, the Spanning Tree Protocol effectively ensures a loop free topology by putting some links into the blocking state and hence constraining the interfaces that use bridge learning. The Spanning Tree Protocol ensures symmetric forwarding behavior. Therefore, while reservation (RESV) messages generated in response to path (PATH) messages are forwarded hop-by-hop at layer 3 of the OSI reference model using path state information set up by the PATH message to effectively force the RESV messages to follow the reverse path of their corresponding PATH messages and data packets, in a layer 2 network MAC layer forwarding based on bridge learning algorithms constrained by the Spanning Tree Protocol, RESV messages will substantially automatically follow the same path as their corresponding PATH messages and data packets at layer 2. As RESV messages will follow the same path as their corresponding PATH messages and data packets a layer 2, there is effectively no need to rely on path state information to route the RESV messages hop-by-hop at layer 2. Hence, with the Spanning Tree Protocol used with respect to layer 2 forwarding, a layer 2 switch or network, e.g., an Ethernet aggregation network, that is positioned in a path substantially between two layer 3 devices is also on the path that will be followed by PATH and RESV messages between the layer 3 devices. As such, if the layer 2 device snoops RSVP messages it may “see” all the RSVP messages associated with a data flow transiting through itself in steady state. In other words, a layer 2 device may effectively see substantially all PATH, RESV, and other RSVP messages associated with the reservation for a flow transiting through itself. 
         [0043]    The ability to identify RSVP messages may be provided in a layer 2 device through the implementation of a classification mechanism that essentially looks inside a layer 2 frame. For example, a classification mechanism may intercept layer 2 frames containing an IP packet with a protocol identifier that indicates RSVP. The RSVP messages intercepted by the classification mechanism may then be handed over to a local RSVP processing agent that processes RSVP messages. The RSVP processing agent allows the layer 2 device to interpret and to forward an RSVP message, as well as to generate error messages when appropriate, e.g., in the case of an admission control rejection by the layer 2 device. 
         [0044]    A layer 2 device which has the capability to identify and process RSVP messages will be described with reference to  FIG. 3A   FIG. 3A  is a block diagram representation of a layer 2 device with RSVP processing capabilities, i.e., a RSVP snooping agent, in accordance with an embodiment of the present invention. A RSVP snooping agent  302  is arranged to receive a packet  304 . Packet  304 , which will be described below with reference to  FIG. 3B , includes a layer 2 header that contains information such as MAC addresses of a sender of packet  304  and an intended receiver of packet  304 . Packet  304  also includes an IP header that includes an IP protocol number, as well as IP address of a sender of packet  304  and a receiver of packet  304 . 
         [0045]    When RSVP snooping agent  302  receives packet  304  on a receiving interface  306 , RSVP snooping agent  302  may access the IP packet header in packet  304  to identify an IP protocol number  308 . If packet  304  is part of a RSVP message, IP protocol number  308  will indicate that RSVP is the protocol associated with packet  304 . In general, IP protocol number  308  is IP protocol number 46 when packet  304  carries an RSVP message. A RSVP processing block  316  of RSVP snooping agent  316  may identify IP protocol number  308 , and may effectively process packet  304 . Processing packet  304  may include determining whether RSVP snooping agent  302  has sufficient resources that may be utilized to receive and to forward RSVP messages. 
         [0046]    As a part of processing packet  304 , RSVP processing block  316  may also access a MAC address table  312  stored in a memory  314  to identify a next hop to which packet  304  may be forwarded. RSVP snooping agent  302  is generally not arranged to perform IP forwarding, and therefore may not utilize a routing table to forward or route packet  304 . MAC address table  312  is used by RSVP snooping agent  302  to, using MAC addresses associated with packet  304 , identify an appropriate interface and virtual local area network (VLAN) for use in forwarding packet  304  towards its intended receiver. 
         [0047]      FIG. 3B  is a representation of a packet, i.e., packet  304  of  FIG. 3A , that may be processed by a RSVP snooping agent, i.e., RSVP snooping agent  302  of  FIG. 3A , in accordance with an embodiment of the present invention. Packet  304  includes a payload area  320  that is arranged to contain data. Packet  304  also includes layer 2 header  324  is arranged to contain information such as MAC addresses and an IP packet header  318 . IP packet header  318  contains IP addresses and an IP protocol number  322  that indicates, in the described embodiment, that packet  304  is associated with a RSVP message. 
         [0048]    RSVP snooping agents such as RSVP snooping agent  302  of  FIG. 3A  may generally be layer 2 devices, e.g., Ethernet bridges or switches. Such RSVP snooping agents may be located individually along a path between IP hops, or in a network that is traversed by a path between IP hops. In other words, a single RSVP snooping agent may be included between two layer 3 or RSVP capable network elements, or a network of RSVP snooping agents may be included between two layer 3 network elements. With reference to  FIG. 4A , an overall network that includes RSVP capable network elements and a network of layer 2 elements in which a resource reservation is to be made will be described in accordance with an embodiment of the present invention. A network  400  includes a sender SRC  404  and a receiver DST  418 . Sender SRC  404  is arranged to initiate a PATH message  422  that is to be forwarded towards receiver DST  418 . In response to PATH message  422 , receiver DST  418  initiates a RESV message  426  that is to be forwarded to sender SRC  404  hop-by-hop. 
         [0049]    When PATH message  422  is sent towards receiver DST  418 , PATH message is provided to a first node  406  which is a layer 3 node with RSVP processing capabilities. First node  406  forwards PATH message  422  to network  412  which, in the described embodiment, is an Ethernet aggregation network. As will be described below with respect to  FIG. 4B , network  412  includes a plurality of RSVP snooping agents. 
         [0050]    Network  412  processes PATH message  422 , and forwards PATH message  422  to a second node  414  or a second hop. Processing PATH message  422  within network  412  may include forwarding PATH message  422  through different snooping agents in network  412  using MAC address tables of the different snooping agents. Second node  414 , which may be a second router, updates MAC addresses in PATH message  406  as appropriate and forwards PATH message  406  to receiver DST  418 . 
         [0051]    RESV message  426  follows the reverse path of PATH message  422  within overall network  400  and within network  412 , as layer 2 path within network  412  is based on the Spanning Tree Protocol in the described embodiment. Hence, nodes  406 ,  414  are arranged to update MAC addresses in RESV message  426 , while snooping agents within network  412  are arranged to perform RSVP processing on RESV message  426 , but are not arranged to update MAC addresses in RESV message  426 . 
         [0052]      FIG. 4B  is a representation of snooping agents within a network  412  in accordance with an embodiment of the present invention. Network  412  includes RSVP snooping agent A  440   a  and RSVP snooping agent B  440   b . RSVP snooping agent A  440   a  is arranged to receive a PATH message substantially directly from first node  406  and to forward a RESV message substantially directly to first node  406 , while RSVP snooping agent B  440   b  is arranged to receive a RESV message substantially directly from second node  414  and to forward a PATH message substantially directly to second node  414 . Any number of snooping agents may generally be included in network  412 . In the described embodiment, however, two snooping agents  440   a ,  440   b  are included in network  412 . 
         [0053]    Nodes  406 ,  414  are border nodes or routers in that nodes  406 ,  414  border network  412 . It should be appreciated that although network  412  is described as being an Ethernet aggregation network, network  412  may be substantially any layer 2 network. Herein and after, for ease of discussion, nodes  406 ,  414  will generally be referred to as routers. However, nodes  406 ,  414  are not limited to being routers and may be substantially any layer 3 network element. 
         [0054]    Router  406  is arranged to cause MAC address tables (not shown) within snooping agents  440   a ,  440   b  to be updated by sending an address resolution protocol (ARP) message through Ethernet aggregation network  412 . Updating the MAC address tables, as per regular Ethernet bridging MAC learning mechanisms, within layer 2 switches that support RSVP snooping agents  440   a ,  440   b  allows snooping agents  440   a ,  440   b  to update their MAC layer forwarding tables using standard Ethernet bridge learning algorithms. Hence, appropriate VLANs and forwarding interfaces to be used to forward an RSVP message towards an appropriate destination for the RSVP message may be accurately determined. Typically, router  406  initiates an ARP message when a PATH message is to be sent to network  412 . Router  414  generally does not initiate an ARP message when a RESV message is to be sent to network  412 , as a previous ARP message sent by router  406  in response to a PATH message has already caused MAC address tables to be updated. 
         [0055]    If a MAC address table (not shown) of snooping agent A  440   a  is not updated before an RSVP message arrives, the RSVP message may be flooded out of substantially all interfaces associated with a VLAN, thereby causing the RSVP message to be forwarded to nodes (not shown) which are not in a path between sender SRC  404  and receiver DST  418  of  FIG. 4A . While this is generally not a concern, because the RSVP states on invalid paths will eventually time out, it is undesirable as it may unnecessarily tie up resources. Hence, as discussed above, before router  406  provides an RSVP message, i.e., a PATH message, to snooping agent A  440   a , router  406  may send an ARP message for the MAC address of the next hop IP address, i.e., the IP address of router  414 . As a result of the ARP message being sent by router  406 , the MAC address tables in the layer 2 devices supporting the RSVP snooping agents  440   a ,  440   b  may be updated. Ensuring that the MAC address tables of the layer 2 switches supporting the RSVP snooping agents  440   a ,  440   b  in network  412  are correctly populated effectively prevents flooding of a message once the message is forwarded by a border router  406 ,  414  through network  412 . 
         [0056]    Referring next to  FIG. 4C , the initiation of an ARP message by router  406  will be described in accordance with an embodiment of the present invention. Router  406  effectively sends an ARP message  450  for the MAC address of router  414 . ARP message  450  typically includes a field describing the message type and a field containing address information. In general, ARP message  450 , when targeted to router  414 , causes MAC address tables  444   a ,  444   b  to be updated or otherwise refreshed. 
         [0057]    It should be appreciated that although ARP message  450  may generally be sent each time router  406  is to forward a PATH message via network  412 , ARP message  450  may not necessarily be sent each time router  406  intends to forward a PATH message. By way of example, if reducing the number of ARP messages sent by router  406  is desired or if scaling is to be improved within a network, ARP message  450  may be sent only in some instances. In one embodiment, ARP message  450  may be sent when a PATH message is to be forwarded substantially only if the Spanning Tree Protocol Topology Change Notification (TCN) message is detected by router  406 . Alternatively, ARP message  450  may be sent substantially only if it is determined that an age of entries in a MAC address table is less than a configurable amount, indicating that a topology change may have occurred recently. 
         [0058]    Each node or network element of a path between a sender and a receiver may perform RSVP processing, regardless of whether the node is a layer 3 node or a layer 2 node.  FIGS. 5A-5C  are a process flow diagram which illustrates one method of processing a PATH message in a network with layer 2 agents that are arranged to use RSVP information for on-path signaling in accordance with an embodiment of the present invention. Processing a PATH message generally entails establishing path states. In the described embodiment, the network is network  400  of  FIG. 4A . A method  500  of processing a PATH message in a network begins at step  502  in which a sender SRC sends a PATH message towards a receiver DST with source and destination IP addresses. In the described embodiment, the sender SRC is sender SRC  404  of  FIG. 4A  which has an IP address of IP_ 0 , and the receiver DST is receiver DST  418  of  FIG. 4A  which has an IP address of IP_ 3 . The PATH message is received and processed by router ‘1’ in step  502 . Router ‘1’ , e.g., node  406  of  FIG. 4A , processes the PATH message as an RSVP message using a routing table to determine the next hop in a path between the sender SRC and the receiver DST. RSVP PATH message processing is typically initiated by a RSVP function in router ‘1’ when the Router Alert IP Option is detected in the IP Header and protocol 46 is detected in a header of the RSVP message. 
         [0059]    Router ‘1’ is aware that in the path between router ‘1’ and router ‘2’, a layer 2 network that supports RSVP snooping is present. More specifically, with respect to  FIG. 4A , node  406  and node  414  are aware that network  412  supports RSVP snooping. Referring back to  FIG. 5A , a determination is made in step  506  regarding whether an error has arisen in the course of RSVP processing. An error may arise for any number of reasons which include, but are not limited to, a lack of an available route between router ‘1’ and the destination. 
         [0060]    If the determination in step  506  is that an error has arisen as a result of RSVP processing, the indication is that the PATH message may not be sent to the destination specified by the destination IP address in the PATH message. Accordingly, in step  507 , a PATH error (PATH_ERR) message is returned towards the sender SRC by router ‘1’. The PATH_ERR message includes the IP address of router ‘1’ as a source IP address that identifies the source of the PATH_ERR message, and the IP address of the RSVP previous hop as the destination of the PATH_ERR message. Once the PATH_ERR message is sent to the Sender SRC, the processing of a PATH message is completed. 
         [0061]    Alternatively, if the determination in step  506  is that an error has not occurred during the course of RSVP processing by router ‘1’, then router ‘1’ sends an ARP message, or “arps,” in step  508  for the next hop IP address in a path. Arping for the next hop IP address causes the MAC address tables of the devices, e.g., switches, in an Ethernet aggregation network to be updated such that the MAC address tables are correctly populated. After router ‘1’ arps for the next hop IP address, router ‘1’ forwards the PATH towards router ‘2’ and, hence, to snooping agent ‘A’ in the Ethernet aggregation network, e.g., snooping agent ‘A’  440   a  of  FIG. 4B , in step  510 . The PATH message is forwarded with a source MAC address specified as the MAC address of router ‘1’ and a destination MAC address specified as the MAC address of router ‘2’, the border router on the other side of the Ethernet aggregation network. It should be appreciated that the source IP address of the PATH message remains the IP address of the Sender SRC and the destination IP address of the PATH message remains the IP address of the receiver DST. 
         [0062]    After receiving the PATH message from router ‘1’, snooping agent ‘A’ identifies the PATH message in step  512  by looking at a header associated with the PATH message, i.e., an IP packet header, and identifying protocol 46. Upon identifying the PATH message, snooping agent ‘A’ performs RSVP processing, which may include updating the PATH message with information on the characteristics of the path, such as delay. Once RSVP processing is performed, it is determined in step  514  whether an error has occurred during RSVP processing. If an error has occurred, e.g., if there is an admission control failure, error processing is performed in step  515 . Methods for performing error processing will be described below with reference to  FIGS. 6A-6C . 
         [0063]    If it is determined in step  514  that an error has not occurred, snooping agent ‘A’ looks up the destination MAC address specified in the Ethernet frame containing the PATH message using a MAC address table in step  516 . Looking up the destination MAC address in the MAC address table of a device that includes snooping agent ‘A’ allows snooping agent ‘A’ to identify a VLAN and an outbound interface to use to forward the PATH message towards the receiver DST. In the described embodiment, the destination MAC address is the MAC address of router ‘2’. 
         [0064]    Snooping agent ‘A’ forwards the PATH message towards the destination in step  518  without modifying IP addresses or MAC addresses specified in the PATH message. In the described embodiment, snooping agent ‘B’, i.e., snooping agent B  440   b  of  FIG. 4B , is in the path between snooping agent ‘A’ and router ‘2’. Hence, the PATH message is forwarded by snooping agent ‘A’ to snooping agent ‘B’ en route to router ‘2’. After snooping agent ‘B’ receives the PATH message, snooping agent ‘B’ identifies the protocol of the PATH message as being protocol 46, and performs RSVP processing in step  520 . 
         [0065]    It is determined in step  522  whether an error has arisen during the course of the RSVP processing by snooping agent ‘B’. If it is determined that an error has arisen, process flow returns to step  515  in which error processing is performed. As previously mentioned, the steps associated with various methods of performing error processing will be described below with respect to  FIGS. 6A-6C . On the other hand, if it is determined in step  522  that RSVP processing has not resulted in an error, then snooping agent ‘B’ looks up the destination MAC address in a MAC address table of the device that contains snooping agent ‘B’ to identify an appropriate VLAN and interface to use to forward the PATH message in step  524 . From step  524 , process flow proceeds to step  526  in which snooping agent ‘B’ forwards the PATH message towards the receiver DST via router ‘2’ without altering the IP addresses and MAC addresses specified in the PATH message. When router ‘2’ receives the PATH message, router ‘2’ processes the PATH message as an RSVP message in step  528 . Processing the PATH message as an RSVP message includes accessing a routing table to determine the next hop to reach the receiver DST. In the described embodiment, the receiver DST is the next hop. It should be appreciated, however, that there may generally be any number of hops between a border router such as router ‘2’ and the receiver DST. 
         [0066]    In step  530 , it is determined whether an error has resulted from the RSVP processing performed by router ‘2’. If it is determined that no error has occurred, router ‘2’ forwards the PATH message to the receiver DST in step  532 . Alternatively, if it is determined in step  530  that an error has occurred, then a PATH_ERR message is generated and transmitted towards the Sender SRC by router ‘2’ in step  532 . The PATH_ERR message is sent towards the Sender SRC with a source IP address set as the IP address of router ‘2’ and a destination address set as the RSVP Previous hop which is the IP address of router ‘1’. The source MAC address in the PATH_ERR message is set to the MAC address of router ‘2’, while the destination MAC address in the PATH_ERR message is set to the MAC address of router ‘1’. The processing of a PATH message is completed after the PATH_ERR message is sent. 
         [0067]    As mentioned above, the error processing methods used by snooping agents, or layer 2 nodes which are capable of RSVP snooping, may vary. In other words, different methods may be associated with step  515  of  FIG. 5A . The method used to process errors may depend upon whether the snooping agent has an IP address and, hence, some IP host functionality, for example. With reference to  FIG. 6A , performing error processing using a snooping agent which has as IP address will be described in accordance with an embodiment of the present invention. A method  515 ′ of processing an error begins at step  602  in which the snooping agent identifies the MAC address of the source of a received PATH message, and uses the MAC address to perform a look up in a MAC address table to determine a forwarding interface for a PATH_ERR message. The MAC address table of a device that includes the snooping agent is used to determine a forwarding interface, because the snooping agent is not running a routing protocol and, therefore, does not have a routing table. Once the forwarding interface is identified, a PATH_ERR message is sent through the forwarding interface in step  604 . The PATH_ERR message is specified with the MAC address of the snooping agent as a source MAC address, and with the MAC address of router ‘1’ as a destination MAC address. The source IP address of the PATH 13  ERR message may be specified as the IP address of the snooping agent, and the destination IP address of the PATH_ERR message may be specified as the IP address of router ‘1’. Upon sending the PATH_ERR message through the forwarding interface, the processing of an error is completed. 
         [0068]    If a snooping agent does not have an IP address, the snooping agent may process an error depending on whether a PATH message is a first PATH message received in a reservation.  FIG. 6B  is a process flow diagram which illustrates another method of performing error processing in response to a PATH message at a snooping agent in accordance with an embodiment of the present invention. A method  515 ″ of processing an error begins at step  608  in which it is determined if the PATH message is the first PATH message received as part of a reservation. If it is determined that the path message is the first PATH message in a reservation, the path message is discarded in step  609 , and the processing of an error is completed. That is, the PATH message is dropped without sending a corresponding error message. It is anticipated that the Sender SRC of the PATH message would eventually be made aware of an error when the Sender SRC fails to receive either an error message or a RESV message in response to the PATH message after a predetermined amount of time. 
         [0069]    Alternatively, if it is determined in step  608  that the PATH message is not the first PATH message in a reservation, the indication is that there is already an established reservation. Hence, the snooping agent has information relating to the IP address and the MAC address of router ‘2’, and may return a PATH_ERR message to the sender SRC that appears to have been sent by router ‘2’. Accordingly, from step  608 , process flow proceeds to step  610  in which the MAC address and the IP address of router ‘2’ are identified from the RESV state maintained for the corresponding reservation. 
         [0070]    Once the MAC address and the IP address of router ‘2’ are identified, the MAC address of router ‘1’ is determined in step  612 , and the MAC address of router ‘1’ is used to look up an appropriate forwarding interface for the PATH_ERR message in the MAC address table of the device that includes the snooping agent in step  613 . Then, in step  614 , the PATH_ERR message is sent through the forwarding interface. The PATH_ERR message has the MAC address of router ‘2’ specified as the source MAC address, the IP address of router ‘2’ specified both as the source IP address and as the RSVP Error Node address which identifies the node in which the error was detected, the MAC address of router ‘1’ specified as the destination MAC address, and the IP address of router ‘1’ specified as the destination IP address. After the PATH_ERR message is sent, the processing of an error is completed. 
         [0071]    A snooping agent may specify dummy addresses as the source addresses of a PATH_ERR message.  FIG. 6C  is a process flow diagram which illustrates a method of performing error processing in which dummy addresses are specified in a PATH_ERR message in accordance with an embodiment of the present invention. A method  515 ′″ of processing an error begins at step  620  in which the MAC address of router ‘1’ is identified from the PATH message that was received by the snooping agent. The identified MAC address of router ‘1’ is used to look up a forwarding interface to use in forwarding a PATH_ERR message in step  622 . Once a forwarding interface is identified, a PATH_ERR message is sent through the forwarding interface in step  624  with a source MAC address and a source IP address each specified as a dummy address. It should be appreciated that the RSVP Error Node Address which identifies the node in which the error was detected may also be specified a dummy IP address. The destination MAC address in the PATH_ERR message is specified as the MAC address of router ‘1’, and the destination IP address in the PATH_ERR message is specified as the IP address of router ‘1’. The processing of an error is completed after the PATH_ERR message is sent. 
         [0072]    The successful receipt of a PATH message by an intended destination, i.e., a receiver, generally results in a RESV message being initiated by the intended destination. With reference to  FIG. 4A , once receiver DST  418  receives a PATH message initiated by sender SRC  404 , receiver DST  418  sends a RESV message towards sender SRC  404  hop-by-hop along the same path traversed by the PATH message. Referring to  FIGS. 7A-7C , one method of processing a RESV message in a network that includes at least one RSVP snooping agent, e.g., network  400  of  FIG. 4A , will be described in accordance with an embodiment of the present invention. A method  700  of processing a RESV message begins at step  702  in which a receiver DST that received a PATH message originates a RESV message to be forwarded to a sender SRC. The RESV message is routed hop-by-hop using path state information that is set up during the course of processing the preceding PATH message. Hence, the RESV message is specified with a destination address of the RSVP previous hop, i.e., the last RSVP hop before the preceding PATH message was received by receiver DST, and a source address of the receiver DST. 
         [0073]    In step  704 , router ‘2’ receives the RESV message from the receiver DST, and processes the RESV message as an RSVP message. During the course of processing the RESV message, router ‘2’ uses the information stored in the PATH state to determine the next hop, i.e., the RSVP previous hop, for the RESV message. A determination is made in step  706  as to whether an error has arisen during RSVP processing. If it is determined that an error has arisen, then a RESV error (RESV_ERR) message is returned to the receiver DST in step  707  with the IP address of router ‘2’ specified as the IP address of the source of the RESV_ERR message, and as the RSVP Error Node Address, and the IP address of the RSVP next hop specified as the IP address of the destination to which the RESV_ERR message is being sent. In the described embodiment, the RSVP next hop is receiver DST in this case. The RESV_ERR message may be sent by router ‘2’ after router ‘2’ uses a routing table to identify an appropriate outbound interface for the RESV_ERR message. Once the RESV_ERR message is returned to the receiver DST, the processing of a RESV message is completed. 
         [0074]    Returning to step  706 , if it is determined that an error has not arisen as a result of RSVP processing, router ‘2’ forwards the RESV message towards the RSVP previous hop, router ‘1’, in the described embodiment. Snooping agent ‘B’ is the next layer 2 hop in a path to the RSVP previous hop, i.e., router ‘1’. The RESV message is forwarded by router ‘2’ with a source MAC address of the RESV message set as the MAC address of router ‘2’, a destination MAC address of the RESV message set as the MAC address of router ‘1’, a source IP address of the RESV message set as the IP address of router ‘1’, and a destination IP address of the RESV message set as the IP address of router ‘2’. 
         [0075]    Snooping agent ‘B’, upon receiving the RESV message from router ‘2’, identifies the RESV message as being an RSVP message in step  712 , and performs RSVP processing, including establishment of the corresponding RESV state . During the RSVP processing performed by snooping agent ‘B’, the source and destination MAC addresses specified in the RESV message are retained. In step  714 , it is determined whether an error has occurred during the RSVP processing. An error may be, in one embodiment, an admission control failure. If it is determined that an error has occurred, error processing is performed in step  715 . The steps associated with error processing may vary widely. Methods for performing error processing will be described below with reference to  FIGS. 8A-8D . After error processing is performed, the processing of a RESV message is completed. 
         [0076]    Alternatively, if it is determined in step  714  that the RSVP processing did not result in an error, then snooping agent ‘B’ obtains the destination MAC address specified in the RESV message and uses the destination MAC address to identify a forwarding interface to use to forward the RESV message in step  716 . The forwarding interface may be identified using a MAC address table stored in the device, e.g., Ethernet switch, supporting snooping agent ‘B’. After the forwarding interface is identified, snooping agent ‘B’ forwards the RESV message towards its intended destination, i.e., router ‘1’ via snooping agent ‘A’ in step  718 . The RESV message is forwarded without modifying MAC and IP addresses specified in the RESV message. 
         [0077]    Snooping agent ‘A’ receives the RESV message, and identifies the RESV message as having protocol 46 in step  720 . Snooping agent ‘A’ also performs RSVP processing on the RESV message. A determination is made in step  722  regarding whether an error has arisen as a result of the RSVP processing. If it is determined that an error has arisen, process flow moves from step  722  to step  715  in which error processing is performed. As previously mentioned, methods for performing error processing will be discussed below with respect to  FIGS. 8A-8D . 
         [0078]    If the determination in step  722  that no error has arisen as a result of the RSVP processing, snooping agent ‘A’ uses the destination MAC address specified in the RESV message to index into a MAC address table in step  724  to identify a VLAN and a forwarding interface to use to forward the RESV message towards its intended destination. Then, in step  726 , snooping agent ‘A’ forwards the RESV message to router ‘1’ without modifying MAC and IP addresses associated with the RESV message. 
         [0079]    When router ‘1’ receives the RESV message, router ‘1’ processes the RESV message as an RSVP message in step  728 , and uses the information stored in the Path state to determine the next hop, i.e., the RSVP previous hop, for sending the RESV message. A determination is made in step  730  as to whether an error has occurred during the RSVP processing. If the determination is that an error has occurred, a RESV_ERR message is returned by router ‘1’ towards the receiver DST, i.e., the source of the RESV message, in step  731 . The RESV_ERR message has its source IP address set as the IP address of router ‘1’ and its destination IP address set as the IP address of the RSVP next hop which is router ‘2’. Once the RESV_ERR message is sent by router ‘1’, the processing of a RESV message is completed. 
         [0080]    Alternatively, if the determination in step  730  is that no error has occurred during the RSVP processing, router ‘1’ forwards the RESV message towards the sender SRC in step  732 , and the processing of a RESV message is successfully completed. The RESV message is forwarded by router ‘1’ with a source IP address of the RESV message set as the IP address of router ‘1’ and a destination IP address of the RESV message set as the IP address of the RSVP previous hop, which is the sender SRC in this case. 
         [0081]    As previously mentioned, methods for performing error processing may vary, Suitable methods for performing error processing will be described below with reference to  FIGS. 8A-8D .  FIG. 8A  is a process flow diagram which illustrates a first method of performing error processing in response to a RESV message at a layer 2 agent that is arranged to use RSVP information for on-path signaling, i.e., step  715  of  FIG. 7A , in accordance with an embodiment of the present invention. A method  715 ′ for performing error processing begins at step  802  in which a MAC address of a source of a received RESV message is identified in a MAC address table. Such an identification allows a forwarding interface for a RESV error message to be determined. Once the MAC address of the source of the received RESV message is identified, a RESV error message is sent in step  804 . The RESV error message is sent to the destination through an interface with a source MAC address specified as the MAC address of the snooping agent, the destination MAC address specified as the MAC address of router ‘2’, the IP source address specified as the IP address of the snooping agent, and the IP destination address specified as the IP address of router ‘2’. After the RESV error message is sent, error processing is completed. 
         [0082]      FIG. 8B  is a process flow diagram which illustrates a second method of performing error processing in response to a RESV message at a layer 2 agent that is arranged to use RSVP information for on-path signaling, i.e., step  715  of  FIG. 7A , in accordance with an embodiment of the present invention. A method  715 ″ for performing error processing begins at step  810  in which the MAC address and the IP address of router ‘1’ are identified from a previous PATH message, or from MAC and destination IP addresses of a RESV message. In step  812 , the MAC address of the source of the RESV message is identified using a MAC address table to determine a forwarding interface for the RESV error message. Finally, in step  814 , a RESV error message is sent through the interface with a source MAC address specified as the MAC address of router ‘1’, the destination MAC address specified as the MAC address of router ‘2’, the IP source address specified as the IP address of router ‘1’, and the IP destination address specified as the IP address of router ‘2’. After the RESV error message is sent, error processing is completed. 
         [0083]      FIG. 8C  is a process flow diagram which illustrates a third method of performing error processing in response to a RESV message at a layer 2 agent that is arranged to use RSVP information for on-path signaling, i.e., step  715  of  FIG. 7A , in accordance with an embodiment of the present invention. A method  715 ′″ of processing an error begins at step  820  in which the amount of requested bandwidth in the RESV message is increased to a high value. Then, in step  822 , the MAC address of the destination of the RESV message is identified using a MAC address table to determine a forwarding interface for the RESV message. From step  822 , process flow moves to step  824  in which the RESV message is sent through the forwarding interface with the source MAC address, the destination MAC address, the source IP address, and the destination IP address as received in the RESV message. When router ‘1’ receives the RESV message, router ‘1’ generates an RESV error message in step  826 . In one embodiment, router ‘1’ generates the RESV error message when the high value of the requested bandwidth in the RESV message is identified. Once the RESV error message is generated, error processing is completed. 
         [0084]    A fourth method of performing error processing in response to a RESV message at a layer 2 agent that is arranged to use RSVP information for on-path signaling, i.e., step  715  of  FIG. 7A , will be described with in accordance with an embodiment of the present invention with respect to  FIG. 8D . A method  715 ″″ of processing an error begins at step  830  in which the MAC address of router ‘2’ is identified from the RESV message. Once the MAC address of router ‘2’ is identified, the MAC address is used in step  832  to look up a forwarding interface in the MAC address table. Then, in step  834 , a RESV error message is sent through the interface with a source MAC address specified as a dummy system address, a destination MAC address specified as the MAC address of router ‘2’, an IP source address specified as a dummy source IP address, and an IP destination address specified as the IP address of router ‘2’. After the RESV error message is sent through the interface, the processing of an error is completed. 
         [0085]    Although only a few embodiments of the present invention have been described, it should be understood that the present invention may be embodied in many other specific forms without departing from the spirit or the scope of the present invention. By way of example, while a network that includes a plurality of layer 2 elements with RSVP snooping capabilities are being described as being in a path between a source node and a destination node, a single layer 2 element may instead be present between the source node and the destination node. Alternatively, layer 2 elements may be interspersed between multiple layer 3 elements along a path between a source node and a destination node. In general, the number of layer 3 nodes and layer 2 nodes in a path between a source node and a destination node, as well as the relative locations of the nodes, may vary widely. 
         [0086]    While RSVP has been described as a protocol that may be snooped to provide layer 2 network elements with on path signaling and admission control capabilities, other protocols may be snooped by layer 2 network elements. That is, the present invention is not limited for use with RSVP, and may also be used for other protocols which provide on path signaling and admission control capabilities. 
         [0087]    In one embodiment, snooping agents or layer 2 nodes with RSVP snooping capabilities may be arranged to further prevent RSVP flooding in an overall network by not relaying snooped RSVP message for which a destination MAC address is unknown. An unknown destination MAC address may be a MAC address that is not present in a MAC address table of a layer 2 node that supports a snooping agent. A snooped RSVP message for which a destination MAC address is unknown may effectively be silently discarded, i.e., the snooped RSVP message may be discarded without sending a corresponding RSVP error message. 
         [0088]    Snooping agents are not limited to being layer 2 nodes with RSVP snooping capabilities. By way of example, some layer 3 nodes may not have RSVP capabilities. For such layer 3 nodes, RSVP snooping capabilities may be provided without departing from the spirit or the scope of the present invention. 
         [0089]    The present invention may be embodied at least in part as code devices or computer code which, in cooperation with processing arrangements, may be executed to enable RSVP processing functionality. In addition, with regards to layer 3 nodes that send ARP messages, the functionality for sending ARP messages may also be embodied as code devices. 
         [0090]    The steps associated with the methods of the present invention may vary widely. Steps may be added, removed, altered, combined, and reordered without departing from the spirit of the scope of the present invention. Therefore, the present examples are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope of the appended claims.