Abstract:
Various embodiments of the invention allow for rapid communication in virtual link trunking (VLT) networks in which network traffic flows over not all-homed VLT peer devices, while honoring Equal Cost Multi Path (ECMP) decisions and normal route decisions about next hops. Traffic flow is made deterministic and free of sub-optimal paths that otherwise cause unnecessary traffic over inter-node links in the VLT domain. In embodiments, this is accomplished by using receiving VLAN interface-IP addresses from VLT devices in order to create and use a sub-LAG egress table from which sets of ports that lead to intended VLT devices are derived. In embodiments, instead of a VLAN interface-IP addresses a routing MAC address is used when forming the sub-LAG.

Description:
BACKGROUND 
       [0001]    A. Technical Field 
         [0002]    The present invention relates to networks and, more particularly, to systems, devices, and methods of routing data in a multipathing domain, such as a Virtual Link Trunking (VLT) network configuration. 
         [0003]    B. Background of the Invention 
         [0004]    When transmitting packets of data using an aggregation interconnection, such as a VLT network, a router has generally no control over which of multiple possible peer devices in the VLT a particular packet will be hashed. If the packet is hashed over a device that is not multi-homed on all VLT peers, an additional hop over an interconnect link (ICL) is therefore likely to occur before the packet is sent to its intended destination. Also, since existing VLT routing and Link Aggregation Group (LAG) hashing are performed over the entirety of a VLT LAG, a packet may reach any next hop ignoring desirable equal-cost multi-path (ECMP) decisions. 
         [0005]      FIG. 1  illustrates an existing VLT network with sub-optimal paths over next hops. Network  100  comprises 3-node VLT LAG domain  102  formed by a group of VLT peer devices  112 - 116 , downstream device router A  130 , upstream devices routers B  132  and C  134 , and host H4  136 . VLT peer devices X  112 , Y  114 , and Z  116  are network switching devices that couple to network nodes via router ports and forward or route traffic according to known data structures that contain routing information. Suitable data structures include routing and next hop tables, e.g., ARP tables that map IP address to routing MAC addresses and its outgoing ports. VLT peer device X  112 , Y  114 , and Z  116  may be coupled to each other, at their ports, via any number of network links, such as ICL  115 . 
         [0006]    As shown in  FIG. 1 , south-bound VLT LAG  120  comprises links that are connected between VLT peer device X  112 , Y  114 , and Z  116  and router A  130 , such that router A  130  may view all VLT peer devices  112 - 116  as a single device or unit having combined ports for purposes of exchanging network traffic with a given destination, such as router A  130 . In other words, router A  130  need not be concerned with which of VLT peer device  112 - 116  receives a data packet that router A  130  sends for performing the requested routing function on the packet. Similarly, north-bound VLT LAG  122  comprises links that connect router B  132  to VLT peer X  112  and Y  114 , i.e., router B  132  is multi-homed on VLT peer X  112  and Y  114 , but is not directly coupled to VLT peer Z  116 . VLT LAG  124  comprises links that connect router C  134  to VLT peer X  112  and Z  116 , i.e., router C  132  is multi-homed on VLT peer X  112  and Z  116 , but not on VLT peer Y  114 . Routers B  132  and C  134  are coupled to destinations host H2  140  and host H3  142 , respectively. Orphan port  126  is directly connected to host H4  136 . In other words, devices that are connected to a VLT LAG are not necessarily also multi-homed. 
         [0007]    In operation, when a packet is to be forwarded from router A  130  to router B  132  intended for host H2  140  or from router A  130  to router C  134  via VLT domain  102  to final destination host H3  142 , and if router A  130  LAG-hashes network traffic to VLT peer Z  116 , then router A  130  has no control over which of VLT peers  112 - 116  the packet will be actually transmitted. In scenarios where the data packet is directed to VLT peer Z  116 , an unnecessary additional hop along ICL  115  will be required to carry traffic to VLT peer Y  114  before the packet can then be transmitted to router B  132 . This creates sub-optimal paths that tends to oversubscribe ICL  113 ,  115 . 
         [0008]    Similarly, any traffic from host H1  144  destined for host H4  136  could get LAG-hashed alternatively to ports on VLT peer X  112  or Y  114 , again, requiring that ICL  113 ,  115  be utilized to carry network traffic. In short, in scenarios where traffic is hashed to VLT peer Z  116 , an additional hop over ICL  115  has to be utilized to detour the traffic to peer Y  114  before data packets can be delivered to router B  132 . 
         [0009]    In fact, in an N-node VLT domain with N&gt;2 there is a likelihood that VLT devices  130 - 136  at the termination of a VLT LAG are not multi-homed on all VLT peers  112 - 116 . Even for 2-node VLT systems, current VLT routing does not guarantee that a packet is routed to the actual next hop, because it is LAG hashing on the VLT that determines the actual next hop that a packet will reach, i.e., which ports coupled to corresponding network links the hashing mechanism will choose to forward any given packet. Thus, sub-optimal network paths may result any time the destination device or an intermediate router is single-homed. 
         [0010]    Further, although both L3-routing and ECMP view individual VLT peers  112 - 116  as next hops, since LAG hashing takes priority over ECMP decisions, traffic may be directed to any of VLT peers  112 - 116  irrespective of ECMP decisions in favor of LAG hashing. 
         [0011]    Therefore, it would be desirable to have systems and methods that honor ECMP decisions while avoiding the creation sub-optimal network paths in networks where the entire VLT LAG is used to perform VLT routing and LAG hashing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Reference will be made to embodiments of the invention, examples of which may be illustrated in the accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in the context of these embodiments, it should be understood that this is not intended to limit the scope of the invention to these particular embodiments. 
           [0013]      FIG. 1  shows an existing VLT network with sub-optimal paths over next hops. 
           [0014]      FIG. 2  illustrates an example VLT network that facilitates a routing scheme according to various embodiments of the invention. 
           [0015]      FIG. 3A  is a flowchart illustrating a routing MAC-based generation of a sub-LAG egress table using the VLT network in  FIG. 2 , according various embodiments of the invention. 
           [0016]      FIG. 3B  is a flowchart illustrating a VLAN/IP based generation of a sub-LAG egress table using the VLT network in  FIG. 2 , according various embodiments of the invention. 
           [0017]      FIG. 4A and 4B  illustrate exemplary sub-LAG egress tables according to various embodiments of the invention. 
           [0018]      FIG. 4C  illustrates an exemplary ARP table in accordance with various embodiments of the invention. 
           [0019]      FIG. 5  is a flowchart illustrating the use of an ARP table according to various embodiments of the invention. 
           [0020]      FIG. 6  depicts a simplified block diagram of an information handling system according to various embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    In the following description, for the purpose of explanation, specific details are set forth in order to provide an understanding of the invention. It will be apparent, however, to one skilled in the art that the invention can be practiced without these details. One skilled in the art will recognize that embodiments of the present invention, described below, may be performed in a variety of ways and using a variety of means. Those skilled in the art will also recognize that additional modifications, applications, and embodiments are within the scope thereof, as are additional fields in which the invention may provide utility. Accordingly, the embodiments described below are illustrative of specific embodiments of the invention and are meant to avoid obscuring the invention. 
         [0022]    Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the invention. The appearance of the phrase “In embodiments,” “in an embodiment,” or the like in various places in the specification are not necessarily referring to the same embodiment. 
         [0023]    The terms “packet,” “datagram,” “segment,” or “frame” shall be understood to mean a group of bits that can be transported across a network. These terms shall not be interpreted as limiting embodiments of the present invention to particular layers (e.g., Layer 2 networks, Layer 3 networks, etc.); and, these terms along with similar terms such as “data,” “data traffic,” “information,” “cell,” etc. may be replaced by other terminologies referring to a group of bits, and may be used interchangeably. 
         [0024]    Embodiments of the present invention presented herein will be described using virtual link trunking (VLT) terminology. These examples are provided by way of illustration and not by way of limitation. One skilled in the art shall also recognize the general applicability of the present inventions to other applications and to other similar technologies that are called by different names. For example, a number of different vendors have implemented their own versions or VLT or VLT-like technologies. For example, Dell Force  10  markets Virtual Link Trunking (VLT). Cisco markets EtherChannel and Port Aggregation Protocol (along with its related Virtual Switching System (VSS), virtual PortChannel (vPC), Multichassis EtherChannel (MEC), and Multichassis Link Aggregation (MLAG)). Avaya markets Multi-Link Trunking (MLT), Split Multi-Link Trunking (SMLT), Routed Split Multi-Link Trunking (RSMLT), and Distributed Split Multi-Link Trunking (DSMLT). ZTE markets “Smartgroup” and Huawei markets “EtherTrunks.” Other vendors provide similar offerings. A standard for this technology is under development in the IEEE  802 . 1  standards committee; the project is called distributed resilient network interconnect (DRNI). Accordingly, references to VLT herein shall be read generally as any similar aggregation/multipathing technology. 
         [0025]    Furthermore, connections between components or between method steps in the figures are not restricted to connections that are affected directly. Instead, connections illustrated in the figures between components or method steps may be modified or otherwise changed through the addition thereto of intermediary components or method steps, without departing from the teachings of the present invention. 
         [0026]    Furthermore, it shall be noted that: (1) certain steps may optionally be performed; (2) steps may not be limited to the specific order set forth herein; (3) certain steps may be performed in different orders; and (4) certain steps may be done concurrently. 
         [0027]    In this document, the terms “hop-to-sub-LAG mapping table,” “sub-LAG egress table,” “next hop-to-sub-LAG mapping table,” and “egress table” are used interchangeably. The term “interface” as used with respect to an Address Resolution Protocol (ARP) table refers to a port or to a sub-LAG if a group of ports are members of the sub-LAG. The term “information handling system” (IHS) comprises any instrumentality or aggregate of instrumentalities operable to compute, calculate, determine, classify, process, transmit, receive, retrieve, originate, route, switch, store, display, communicate, manifest, detect, record, reproduce, handle, or utilize any form of information, intelligence, or data for business, scientific, control, or other purposes. For example, the IHS may be a personal computer (e.g., desktop or laptop), tablet computer, mobile device (e.g., personal digital assistant or smart phone), server (e.g., blade server or rack server), a network storage device, or any other suitable device and may vary in size, shape, performance, and functionality. The IHS may include random access memory, one or more processing resources, (e.g., CPU) or hardware or software control logic, ROM, and/or other types of nonvolatile memory. Additional components of the IHS may include one or more disk drives, one or more network ports for communicating with external devices as well as various input and output (I/O) devices, such as a keyboard, mouse, touchscreen and/or video display. The IHS may also include one or more buses operable to transmit communications between the various hardware components. 
         [0028]      FIG. 2  illustrates an example VLT network that facilitates a routing scheme according to various embodiments of the invention. Network  200  comprises 3-node VLT LAG domain  202  formed by a group of VLT peer devices  212 - 216 . VLT peer devices  212 - 216  are coupled north-bound to VLT LAG  222  and  224  comprising VLAN 30 and VLAN 20, respectively. Also shown in  FIG. 2 , host H4  136  is coupled to VLT Peer Z  216  and south-bound VLT LAG  220  that comprises VLAN 10. Each VLT peer device X  212 , Y  214 , and Z  216  in VLT LAG domain  202  is connected to router A  130  via links that are members of respective sub-LAG  250 ,  252 , and  254 . It shall be noted that  FIG. 2  is provided by way of example to help facilitate illustration of methods according to embodiments of the present invention. One skilled in the art shall recognize that aspects of the present invention may be applied to a vast array of different types of network configurations. For example, one skilled in the art will appreciate that although  FIG. 2  displays network  200  in a 3-node VLT LAG domain configuration  202 , any number of VLT peer devices having network links may be used and may be coupled to any number of network devices directly or via VLT LAGs. Further, routers  130 - 136  represent any network node, including switches or other information handling systems. 
         [0029]      FIG. 3A  is a flowchart illustrating a routing MAC-based generation of a sub-LAG egress table using the VLT network in  FIG. 2 , according various embodiments of the invention. The process for generating the sub-LAG egress table includes step  302  where packets from each VLT peer are received at a routing device, such as a router. In embodiments, the packets comprise LLDP with organization specific TLV and the VLT peer&#39;s routing MAC address. 
         [0030]    At step  304 , a sub-LAG egress table is updated with VLT peer neighbor, routing MAC, and port list information. 
         [0031]    At step  306 , the set of interfaces or ports from where LLDP with identical routing MAC organization specific TLV is received from VLT peer is grouped to form a sub-LAG at step  308 . 
         [0032]    At step  310 , for each resolved ARP entry whose routing MAC matches that received from the VLT peer, the outgoing interface information with newly formed SUB-LAG is updated. 
         [0033]    The sub-LAG egress table comprising sub-LAGs with unique sub-LAG IDs (e.g.,  100 - 102 ) may be generated using a Link Layer Discovery Protocol (LLDP) mechanism. The LLDP format typically supports an organization-specific TLV (type-length-value). 
         [0034]      FIG. 3B  is a flowchart illustrating a VLAN/IP based generation of a sub-LAG egress table using the VLT network in  FIG. 2 , according various embodiments of the invention. In embodiments, each routing information may comprise a VLAN ID and a VLT peer device IP address. Process  350  for generating the sub-LAG egress table includes step  352  where packets from each VLT peer are received at a routing device, such as a router. In embodiments, the packets comprise LLDP with organization specific TLV and the VLT peer&#39;s (VLAN, IP) pair information. 
         [0035]    At step  354 , a sub-LAG egress table is updated with VLT peer neighbor, (VLAN, IP) pair, and port list information. 
         [0036]    At step  356 , the set of interfaces or ports from where LLDP with identical (VLAN, IP) pair organization specific TLV is received from VLT peer is grouped to form a sub-LAG at step  358 . 
         [0037]    It will be appreciated by those skilled in the art that additional steps may be incorporated with the steps illustrated herein without departing from the scope of the invention. Packets may be sent from any physical interface. For example, router A  130  in  FIG. 2  may send out packets from ports 0-5 and, similarly, LLDP-enabled VLT peer devices  212 - 216  may send out LLDP packets from physical ports. Each physical interface or routing interface (e.g., VLAN 10  220 ) may be associated with both a MAC address and an IP address, such that a physical interface having an IP address may also have a different MAC address. 
         [0038]    In embodiments, the LLDP data units with organization-specific TLV are encoded in the MAC address and include in an LLDP specific TLV a unique routing MAC address for each VLT peer device  212 - 214  (e.g., M1 for VLT peer X  212 ), such that each set of links leading from VLT peer device  212 - 214  to router A  130  will receive LLDP packets associated with its respective VLT peer device  212 - 214 . The organization-specific TLVs that point to a same MAC address, i.e., are associated with the same VLT peer device  212 - 214 , point to the same physical layer. For example, two distinct links from VLT peer X  212  to router A will carry the LLDP packet on both links such that router A  130  receives LLDP data units on port 0 and 1 from VLT peer X  212 . 
         [0039]    Using the LLDP information, router A  130  may form a corresponding sub-LAG by bundling a set of links that connects to VLT peer X  212 —a single physical device,—but does not lead to both VLT peer X  212  and VLT peer Y  214  at the same time. By extension, if an LLDP packet is received on N distinct links calling unique TLVs that carry the same MAC address, the N links may be bundled into a specific sub-LAG. 
         [0040]    In embodiments, router A  130  associates this routing information with the identified sub-LAGs to generate a sub-LAG egress table that assigns a subset of ports and a sub-LAG ID to each sub-LAG. With the creation of the sub-LAG egress table with the routing information and sub-LAGs, it is known which output ports of router A  130  will reach VLT peer X  212 . 
         [0041]      FIG. 4A  illustrates an exemplary sub-LAG egress table according to various embodiments of the invention. In embodiments, sub-LAG egress table  400  is used as an outgoing interface for ARP information to reach individual VLT devices. In example in  FIG. 4A , table  400  is a sub-LAG egress LLDP egress table that comprises a column for storing routing MAC addresses  404  and a column for corresponding port lists  406  that each represent a subset of egress ports. Each egress port designates next hops within a path, wherein each next hop has a routing MAC address  404 . 
         [0042]    In embodiments, egress table  400  uses LLDP information to create sub-LAGs  408  that contain subsets of ports that lead to individual VLT devices. For example, VLT peer devices X-Z  422 ,  432 , and  442  may have respective unique routing MAC addresses  424 ,  434 , and  444  M1-M3 in an LLDP organization-specific TLV. VLT peer X  422  may send on ports 0 and 1  426  an LLDP packet with the same routing MAC address  424 , M1, indicating that these two links  426  lead to a single physical device, VLT peer X  422 , having that physical MAC address  424 . In this example, sub-LAG  408  is formed using links  426  to identify the specific physical device, VLT peer X  422 , and sub-LAG ID  100   428  is assigned to sub-LAG  408 . 
         [0043]    Similarly, VLT peer Y  432  sends on port 2 and 3  436  an LLDP packet with the identical routing MAC address  434 , M2, indicating these two ports  436  are connected to a physical device identified by that physical MAC address. From this information a sub-LAG is formed and, again, sub-LAG ID  101   438  is assigned. For VLT peer Z  442  having MAC address M3  444  a sub-lag with ports 4 and 5  446  is formed and associated with sub-LAG ID  102   448 . Packets ingres sing at a router from any of VLT peer devices X-Z  422 ,  432 , and  442  may be associated with a parent LAG (not shown) having a parent LAG ID that comprises all six ports 0-5. 
         [0044]    The egress table in  FIG. 4B  enables a similar approach, except that instead of unique routing MAC addresses, VLAN and IP addresses  454  are used to identify port lists  456  that designate next hops to reach peer devices  452  having unique IP addresses. Egress table  450  comprises a column  452  for storing routing VLANs that the LLDP TLV carries with corresponding IP addresses of peer devices that have logical interfaces (here VLAN 10) assigned and a column for storing a corresponding ports list  476 . As a result, a router may communicate only to VLAN 10 VLT on peer X  472 , such that when the router resolves an ARP for a given next hop address learned through the routing protocol, it can receive the IP address IP1 on VLAN 10 and knows that it is trying to resolve the IP address for IP1 on VLAN 10. Similarly, a router (e.g., router B) coupled to VLAN 30 may assign a routing information (VLAN 30, IP 4) to VLT peer X and a routing information (VLAN 30, IP 5) to VLT peer Y. 
         [0045]    Ports list  476  in table  450  in  FIG. 4B  includes a subset of egress ports that designate a next hop in a path to reach a given routing IP address. In embodiments, first, each of the logical interfaces of VLT peer devices  452  is configured in an organization-specific TLV to have a corresponding IP address that can serve as the next hop. For example, VLAN 10 is configured and an individual IP address IP1 (e.g., 10.1.1.1) is assigned to VLT peer X  472  at VLAN 10. Likewise, the configuration for VLT peer Y  482  uses the same VLAN 10 but is assigned a different IP address IP2 (e.g., 10.1.1.2), such that with respect to router A, the typical next hops in the VLT path to reach host 2 on VLAN 10 will be IP1 and IP2. 
         [0046]    In embodiments, an organization-specific LLDP TLV will carry all VLANs and corresponding IP addresses  474 . Since each of the IP addresses is LLDP information, a lookup in an ARP table will be based on LLDP information of the VLAN-IP combination. Paths matching sets of outgoing ports 0 and 1  476  then form single sub-LAG  478 . In other words, in order to identify sub-LAG  458  for VLT peer device  472 , instead of carrying a routing MAC address of the device  452 , as was illustrated in  FIG. 4A , for each VLAN, a specific data set comprising VLAN ID and corresponding IP address  454  is configured, as shown in  FIG. 4B . This data set is used to identify sub-LAG  458  leading to a particular VLT device. In this example, a specific sub-LAG  458  is formed for any two ports  456  (e.g., 0 and 1) that carry the same LLDP packet and organization-specific TLV content. One skilled in the art will appreciate that, depending on network configuration, tables  400  and  450  may comprise rows and columns for any number of VLT peer devices, addresses, pairs, port lists, sub-LAGs, to associate information contained in two or more columns with each other. 
         [0047]    It is noted that in organization-specific LLDP TLV only one unique routing MAC address is included per logical interface or VLAN even if, for example, a router may house one unique MAC address per routing interface. In such instances, this embodiment may provide no mechanism to identify multiple MAC addresses for all VLANs, e.g., when each VLT peer device  422 - 442  sends out only one unique routing MAC address per switch. Therefore, when peer device  422 - 442  receives a packet with that MAC address, it may not be able to correctly identify each sub-LAG when performing its IP lookup in preparation to routing a packet. 
         [0048]    Once sub-LAGs are identified in the egress table, they may be used to program an ARP table of a router, for example, when processing an ARP response to resolve requests. Address resolution generally requires that for each IP address a corresponding MAC address be known. At the control plane level, where information about routes is learned by inspecting data traffic, once an ARP response is received, the MAC address can be determined therefrom. 
         [0049]      FIG. 5  is a flowchart illustrating the use of an ARP table according to various embodiments of the invention. The process for using the ARP egress table begins, at step  502 , when packets are received, for example, at a routing device from a host sending the packet to an intended host in a network path. 
         [0050]    At step  504 , a next hop routing address is determined from a route table that may be stored in memory. 
         [0051]    Based on the next hop routing address, at step  506 , an egress interface entry is looked up in an ARP table. In embodiments, the egress interface entry corresponds to the routing information previously mentioned with respect to  FIGS. 3A-B  and  4 A-C. 
         [0052]    Once the entry is found in the ARP table, then, at step  508 , the egress interface is determined from the ARP table. 
         [0053]    Finally, at step  510 , the sub-LAG is used for egress, for example, by forwarding packets to an intended VLT node. One skilled in the art will appreciate that fewer or additional steps may be incorporated with the steps illustrated herein, and that no particular order is implied by the arrangement of blocks within the flowchart or its description. 
         [0054]    With reference to  FIG. 2 , assuming router A  130  knows that VLT peer X  212  is identified by IP address IPx (e.g., 10.1.1.1), then router A  130  also knows the corresponding MAC address (e.g., M1—the same MAC address that router A  130  already uses for the LLDP). In embodiments, router A  130  receives routing information in the ARP response and looks up a matching sub-LAG correspondence in a sub-LAG egress table. A lookup in LLDP egress table in  FIG. 4A , for example, reveals that MAC address M1  424  refers to VLT peer X, port list (0,1)  426 , and a sub-LAG having sub-LAG ID  100   428 . Router A may use that information to build its ARP table and attempt to resolve the ARP for a given next hop address learned through the routing protocol. 
         [0055]      FIG. 4C  illustrates an exemplary ARP table according to various embodiments of the invention. In addition to information about IP-to-MAC mapping, ARP table  480  comprises information about egress interface  414 , e.g., a sub-LAG coupled to the next hop for which the ARP is resolved. In embodiments, router A places the looked-up sub-LAG information  464  into its hardware ARP table  480  such that physical interfaces  414  corresponding to a sub-LAG may be used as next hop routing information, for example, to point to sub-LAG  200   464 , which as learned from VLT peer X comprises outgoing ports 0 and 1. For each ARP that is resolved per VLAN, the corresponding routing MAC address  462  may be looked up in the egress table and the port list for each sub-LAG  464  may be derived based on that address. 
         [0056]    In embodiments, pointing to the sub-LAG is not based on a MAC address for an IP address on a particular VLAN as in  FIG. 4A , but rather on the routing information of the VLAN10-IPx combination (illustrated in  FIG. 4B ) that the router tries to resolve. As a result, when trying to resolve ARP on VLAN10 for a given next hop address, e.g., VLT peer X at address IP1  474 , upon receiving an ARP response, instead of using the MAC address for IP1 to look up a corresponding port list in the egress table, the VLAN-IP address combination  454  is used to look up the port list, so that the corresponding sub-LAG can be obtained based on the combination. 
         [0057]    Finally, information about egress interface can be programmed into the ARP table, written into the hardware of router A, and made available for subsequent packets as an outgoing port for the ARP information to serve as next hop. Programming the ARP table into the hardware forces packets to be sent via a given VLT peer device to use a particular one of the sub-LAGs that leads to the corresponding VLT peer device. 
         [0058]    In embodiments, for each of the parent port channels on which the ARP response would have been received, the parent port channel is replaced with a sub-LAG, such that traffic destined for forwarding to the VLT peer points to the corresponding sub-LAG instead of pointing to the parent port channel. In  FIG. 2 , for example, instead of pointing to parent VLT LAG  220  that includes all ports 0-5 of router A  130  and, thus, includes a path to VLT peer Z  216 , VLT peer X  212  may be programmed to identify a particular sub-LAG comprising member ports to ensure that the packet will directly flow, for example, to VLT peer X  212 , and not to VLT peer Y  214  or VLT peer Z  216  before the packet is routed to destination host H2  140 . Similarly, if VLT peer Y  214  is elected to reach host H2  140 , the sub-LAG to which VLT peer Y  214  may be programmed will ensure that the packet flows to VLT peer Y  214  prior to being routed to router B  132 , which then forwards the packet to destination host H2  140 . 
         [0059]    An ARP response from, e.g., VLT peer Y received with a MAC address M2 (as identified in LLDP egress table  FIG. 4A , and that would otherwise be associated with the parent port channel in the control plane) may be used to look up in table  400  that M2 MAC address  434  corresponds to VLT peer Y and identifies sub-LAG  101   438 . Sub-LAG  101   438  may then be programmed into an ARP table in order to point to ports 2 and 3  436  that can reach VLT peer Y  214  (e.g., 10.1.1.2). In short, from information learned when an ARP response containing a device&#39;s MAC address is received, VLT content that is based on routing MAC address  404  is looked up, sub-LAG  408  is identified, and the router updates the ARP table to have its interface column point to a sub-LAG  408  instead of a parent LAG that includes all ports of the router. 
         [0060]    As a result, the ARP response sent by VLT peer X  212  in  FIG. 2 , for example, will be received on router A  130  sent from hardware associated with the appropriate ports with the effect that when router A  130  performs load balancing, VLT peer Z  216  is excluded as a possible path to route the packet to host H2  140 , while network  200  continues to honor ECMP routing decisions and is not prone to looping issues. In other words, VLT peer Z  216  is not involved, at all, as might happen if VLT LAG  220  were identified instead of a sub-LAG. 
         [0061]    In contrast, prior art routing schemes use a parent VLT LAG that includes all ports 0-5 of router A  130 . However, the parent VLT LAG has no control over which of VLT peers  212 - 216  a particular packet is sent. Therefore, existing designs may disadvantageously choose VLT peer Z  216  to route the packet to host H2  140 . Such a detour over a sub-optimal path, however, unnecessarily increases network processing that adds delay. 
         [0062]    In embodiments, incoming traffic at router A  130  from any of VLT devices  212 - 216  is associated with parent VLT LAG  220  while leaving the ingress LAG table unmodified. As a result, broadcast traffic is prevented from looping back to any of VLT peer devices  212 - 216 . It is noted that even if sub-LAG  250 - 254  may be associated with multiple ports (e.g., sub-LAG  252  comprises ports 0 and 1), this has no harmful effect as all ports sub-LAG  250 - 254  may direct network traffic to the same physical device and not to any other device before packets are then routed to a router that forwards the packets to the desired host. In this manner, the traffic to a destination pointed to by an intended next hop will be used, thereby, avoiding oversubscription of ICL links. 
         [0063]    In embodiments, in case of a failure in the sub-LAG links, the ARP entries are updated with reassigned entries that point to the parent VLT LAG, such that traffic can be forwarded via the parent VLT LAG to ensure packets still reach their intended destination. 
         [0064]      FIG. 6  depicts a simplified block diagram of an information handling system according to various embodiments of the present invention. It is understood that the functionalities shown for device  600  may operate to support various embodiments of an IHS (or node)—although it is understood that an IHS may be differently configured and include different components. IHS  600  may include a plurality of I/O ports  605 , bus  610 , network processing unit (NPU)  615 , one or more tables  620 , and CPU  625 . The system includes a power supply (not shown) and may also include other components, which are not shown for sake of simplicity. 
         [0065]    In embodiments, I/O ports  605  are connected via one or more cables to one or more other network devices or clients. Network processing unit  615  may use information included in the network data received at node  600 , as well as information stored in table  620 , to identify a next hop for the network data, among other possible activities. In embodiments, a switching fabric then schedules the network data for propagation through the node to an egress port for transmission to the next hop. 
         [0066]    It is noted that aspects of the present invention may be encoded on one or more non-transitory computer-readable media with instructions for one or more processors to cause steps to be performed. It is also noted that the non-transitory computer-readable media may include volatile and non-volatile memory. It is noted that alternative implementations are possible, including hardware and software/hardware implementations. Hardware-implemented functions may be realized using ASICs, programmable arrays, digital signal processing circuitry, and the like. Accordingly, the “means” terms in any claims are intended to cover both software and hardware implementations. Similarly, the term “computer-readable medium or media” as used herein includes software and/or hardware having a program of instructions embodied therein, or a combination thereof. With these implementation alternatives in mind, it is understood that the figures and accompanying description provide the functional information one skilled in the art would require to write program code (i.e., software) and/or to fabricate circuits (i.e., hardware) to perform the processing required. 
         [0067]    One skilled in the art will recognize that no particular IHS, protocol, or programming language is critical to the practice of the present invention. One skilled in the art will also recognize that a number of the elements described above may be physically and/or functionally separated into sub-modules or combined together. 
         [0068]    It will be appreciated to those skilled in the art that the preceding examples and embodiments are exemplary and not limiting to the scope of the present invention. It is intended that all permutations, enhancements, equivalents, combinations, and improvements thereto that are apparent to those skilled in the art upon a reading of the specification and a study of the drawings are included within the true spirit and scope of the present invention.