FabricPath Configuration Guide, Cisco DCNM for LAN, Release 5.x
FabricPath Forwarding
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FabricPath Forwarding

Table Of Contents

FabricPath Forwarding

Information About FabricPath Forwarding

FabricPath Forwarding Overview

FabricPath VLANs

Forwarding Known Unicast Packets Using ECMP

Forwarding Trees for Broadcast, Unknown Unicast, and Multicast Packets

Forwarding Multicast Packets

Creating Multiple Nondefault FabricPath Topologies

High Availability

Licensing Requirements for FabricPath Forwarding

Platform Support

Configuring Additional, Nondefault Topologies using DCNM (Optional)

Configuring Additional Nondefault Topologies on One Device (Optional)

Configuring Additional Topologies on Multiple Devices Using the FabricPath Wizard (Optional)

Displaying Information about the FabricPath Network

Displaying Basic FabricPath Network Information

Displaying FabricPath Interface Network Information

Displaying Reachability Information

Field Descriptions for FabricPath Forwarding Information

Fabricpath Topology: Fabricpath Topology Details: Basic Settings Section

Fabricpath Topology: Fabricpath Topology Details: Interface Settings Section

Fabricpath Topology: Reachability Status: Reachability Status Section

Feature History for Configuring FabricPath Using the DCNM


FabricPath Forwarding



Note See the Cisco DCNM Fundamentals Configuration Guide for more information on displaying the FabricPath topologies.


This chapter describes the forwarding behavior of FabricPath on the Cisco Nexus 7000 Series NX-OS devices.

This chapter includes the following sections:

Information About FabricPath Forwarding

Licensing Requirements for FabricPath Forwarding

Platform Support

Configuring Additional, Nondefault Topologies using DCNM (Optional)

Displaying Information about the FabricPath Network

Field Descriptions for FabricPath Forwarding Information

Feature History for Configuring FabricPath Using the DCNM

Information About FabricPath Forwarding


Note You must have an F Series module in your chassis to run FabricPath.


This section includes the following sections:

FabricPath Forwarding Overview

FabricPath VLANs

Forwarding Known Unicast Packets Using ECMP

Forwarding Trees for Broadcast, Unknown Unicast, and Multicast Packets

Creating Multiple Nondefault FabricPath Topologies

High Availability

FabricPath Forwarding Overview

Beginning with Cisco Release 5.2(1) for the Cisco Nexus 7000 Series devices, you can create additional, nondefault FabricPath topologies. You can create up to three topologies in addition to the default topology (topo0); each topology creates two trees. See "Creating Multiple Nondefault FabricPath Topologies" section for information on creating additional topologies.

FabricPath provides a multipath Layer 2 domain that does not require STP for a loop-free environment. Using the Intermediate System-to-Intermediate System (IS-IS) protocol, the device provides multiple paths for Layer 2 packets.

Each FabricPath interface can learn multiple parallel paths to the other nodes in the FabricPath network. Because you do not need to use STP, all the paths are available for forwarding traffic. The device assigns the optimal path per flow.

The flow for known unicast packets is determined by the hierarchical FabricPath Outer Destination Address (ODA) and the Outer Source Address (OSA) value (see Chapter 3 "Configuring FabricPath Switching" for more information on FabricPath hierarchical encapsulation). The system uses IS-IS Equal Cost Multipathing (ECMP) to choose the forwarding path for these flows, using FabricPath Layer 2 IS-IS.

For multidestination traffic (unknown unicast, broadcast, and multicast), the FabricPath system creates two paths, or trees. The broadcast and unknown unicast traffic flows through one of these trees. The system distributes the multicast traffic between the two trees based on a hash. Thus, the system load balances multicast traffic in the FabricPath network (see "Forwarding Trees for Broadcast, Unknown Unicast, and Multicast Packets" section for more information).

FabricPath Layer 2 IS-IS defines the trees. The highest system ID is chosen for the root and the tree flows from that. The system ID is configurable per device. The second tree is the same but with a different root priority. After the system chooses the root switch, the tree is built with that as the root for the first tree. Then, the root switch for the first tree elects the root of the second tree, again based on system ID, and the second tree flows from that root switch. All of this information is advertised to the FabricPath network using Layer 2 IS-IS, so all the devices have in the network have the same information.

The system assigns the path at ingress and encodes that path in the FTag portion of the FabricPath header. The system assigns one FTag per tree. Once decided and tagged, the packet uses the same tree throughout the entire FabricPath network. All the nodes in the FabricPath network forward traffic based on this same information because all nodes have the same information using Layer 2 IS-IS.

The FabricPath frame has a Reverse Path Forwarding (RPF) mechanism for multidestination packets, which verifies that the packet is arriving on an interface that leads to the source switch. RPF drops the packet if it is received from an interface that is not part of the tree.

The FabricPath Layer 2 IS-IS protocol floods the link-state information across the FabricPath network. Each device sends hello packets on each FabricPath link and discovers its neighbors. When a neighbor is discovered, the system creates an IS-IS adjacency. Each device also sends advertisements and updates to the link-state database through all the existing adjacencies.

FabricPath VLANs

To interact with the Classical Ethernet (CE) network, you set VLANs to either CE or FabricPath (FP) mode. The CE VLANs carry traffic from the CE hosts to the FabricPath interfaces, and the FP VLANs carry traffic throughout the FabricPath topology. Only the active FP VLANs configured on a switch are advertised as part of the topology in the Layer 2 Intermediate System-to-Intermediate System (IS-IS) messages.


Note For information on changing the VLAN mode from Classical Ethernet (CE) to Fabricpath (FP), see the Cisco DCNM Layer 2 Switching Configuration Guide.


The system automatically assigns all FabricPath interfaces and FP VLANs to the topology. So, there is no added configuration required. (See Chapter 4 "FabricPath Interfaces" for information on FabricPath interfaces.) All the FP VLANs and FabricPath interfaces belong to that same topology. All ports on the same device in the same topology must be in the same VDC.


Note When you create additional, nondefault topologies, you must assign the specific FabricPath interfaces and the FabricPath VLANs to the specific topology.


Figure 5-1 shows a sample FabricPath topology with Classical Ethernet switches and FP/CE VLANs.

Figure 5-1 Example FabricPath Topology and Classical Ethernet Hosts

The default VLAN mode on the device is the CE VLAN mode. The FabricPath interfaces carry traffic only on the FP VLANs; the CE VLANs do not come up on these interfaces. The CE interfaces on the F Series modules carry traffic for both CE VLANs (traffic from the hosts) and FP VLANs.

You must exit the VLAN configuration mode for the VLAN mode change to take effect.


Note Once you configure VLANs and interfaces, no further configuration is required. The system automatically creates and assigns the paths, as well as provides load balancing.


Forwarding Known Unicast Packets Using ECMP

The system forwards unicast traffic per flow using the ODA field in the FabricPath header for known unicast traffic. The FabricPath-enabled system assigns the switch ID and the ODA for all encapsulated traffic at the ingress switch. (See Chapter 3 "Configuring FabricPath Switching" for more information on FabricPath encapsulation.)

Once the system assigns the ODA, the FabricPath device uses the FabricPath Layer 2 IS-IS ECMP to forward known unicast traffic. FabricPath, using Layer 2 IS-IS, has up to 16 active Layer 2 paths. This feature provides up to 16-way ECMP at Layer 2 for all known unicast packets. The Layer 2 IS-IS messages used by FabricPath are separate and distinct from the Layer 3 IS-IS messages used by the routing protocols and the Overlay Transport Virtualization (OTV).

The devices within the FabricPath network exchange topology information using IS-IS adjacencies and forward the traffic along those paths for known unicast traffic flows. Each node in the FabricPath network looks at the FabricPath header for each traffic flow and makes an ECMP forwarding choice based on the available next hops.

Forwarding Trees for Broadcast, Unknown Unicast, and Multicast Packets

FabricPath introduces a new loop-free broadcast functionality that carries broadcast, unknown unicast, and multicast packets, or multidestination traffic. For each broadcast, unknown unicast, and multicast traffic flow, the system chooses the forwarding path from among multiple system-created paths or trees. For this release, the system creates two trees to forward the multidestination traffic for each topology.

For the FabricPath network, the system creates a broadcast tree that carries broadcast traffic, unknown unicast traffic, and multicast traffic through the FabricPath network. The system also creates a second tree; all the multicast traffic flows are load balanced across these two trees for each flow. Each tree is identified in the FabricPath network by a unique value, or FTag. Within the FabricPath network, the system elects a root node that becomes root for the broadcast tree. That node also identifies another bridge to become root for the second multidestination tree, which load balances the multicast traffic.

The FTag is assigned by the ingress switch, along with the ODA and OSA, as part of the FabricPath encapsulation. The FTag determines which loopfree tree the multidestination traffic flow follows through the FabricPath network. The system assigns the trees per flow.

Figure 5-2 shows these trees.

Figure 5-2 Trees for Forwarding Multidestination FabricPath Flows for a Given Flow

Each node in the FabricPath network shares the same view of the forwarding trees for a given FTag.

Forwarding Multicast Packets

Using FabricPath and an F Series module, you can configure Layer 2 multicast multipathing. FabricPath uses a hash-based system to assign each of the multicast flows to one of the two designated trees to ensure that the multicast traffic is load balanced.

The system uses FabricPath Layer 2 IS-IS in conjunction with Classical Ethernet IGMP Snooping to learn the multicast group information at the boundaries of the FabricPath/Classical Ethernet network. The system carries that information through the FabricPath network using a new Layer 2 IS-IS LSP called Group Membership LSP (GM-LSP). GM-LSPs carry multicast group/source membership information. This information is carried across the FabricPath network. All FabricPath switches maintain multicast routing information and forward multicast data packets only to switches that have interested receivers. Each node in each FabricPath topology shares the same view and has all the same information.

The multicast traffic uses the per-VLAN source, multicast group, and flow information to allocate traffic to one or the other of the two trees. This system constrains multicast based on the group IP address.

IGMP snooping and FabricPath IS-IS, using GM-LSP, work together to build per-VLAN multicast group-based trees across the FabricPath network. IGMP snooping on edge interfaces learns of receivers and routers and builds an edge-port multicast state. FabricPath Layer 2 IS-IS propagates this attached group information through the FabricPath network using GM LSPs, building a state in the FabricPath network. Devices at the edge of the FabricPath network that have multicast groups originate the GM-LSP.

For Layer 2 multicast traffic, you need not run PIM at all when using FabricPath.

For Layer 3 multicast packets, the system sets the ODA to a special multicast group that identifies all IP routers for that group and forwards the traffic along the tree for that group.

Creating Multiple Nondefault FabricPath Topologies

You can create additional, nondefault FabricPath topologies to provide multiple paths through the FabricPath network. You can create up to three additional topologies, and each topology has two trees. If you use topologies other than the default topology, you must assign the FP VLANs and FabricPath interfaces to a newly created topology.

A FabricPath interface can belong to multiple FabricPath topologies, and multiple FabricPath interfaces can be configured with the same topology.

The FabricPath topology functions analogously to the Multiple Spanning Tree (MST) protocol in that you assign a group of VLANs to one instance in MST and to one topology using FabricPath. One VLAN can belong to only one FabricPath topology.

Each VLAN can have its own topology or a group of VLANs can share a topology. If you are not using the default FabricPath topology, you assign the FP VLAN to an FabricPath topology. Basically, you associate topologies, rather than VLANs, to all the FabricPath interfaces. The system maintains a table that shows each FabricPath interface and the alternate topologies available on the device.

You use created, nondefault FabricPath topologies for traffic separation and traffic engineering (see Figure 5-3.

Figure 5-3 Default and Additional FabricPath Topologies


Note Once you configure the topology or topologies, VLANs, and interfaces, no further configuration is required. The system automatically creates and assigns the paths, as well as providing load-balancing.


The new topology comes up on a FabricPath interface when the first VLAN comes onto that interface. And when the last FabricPath VLAN on that interface goes down, the topology goes down for that interface.

High Availability

The FabricPath topologies retain their configuration through ISSU.

See the Cisco Nexus 7000 Series NX-OS High Availability and Redundancy Guide, Release 5.x, for more information on high availability.

Licensing Requirements for FabricPath Forwarding

The following table shows the licensing requirements for this feature:

Product
License Requirement

Cisco NX-OS

FabricPath requires an Enhanced Layer 2 license. For a complete explanation of the Cisco NX-OS licensing scheme, see the Cisco Nexus 7000 Series Licensing Guide.

Cisco DCNMS

FabricPath requires no license. For a complete explanation of the DCNM licensing scheme, see the Cisco DCNM Installation and Licensing Guide, Release 5.x.


Platform Support

The following platform supports this feature. For platform-specific information, including guidelines and limitations, system defaults, and configuration limits, see the corresponding documentation.

Platform
Documentation

Cisco Nexus 7000 Series Switches

Cisco Nexus 7000 Series Switches Documentation


Configuring Additional, Nondefault Topologies using DCNM (Optional)


Note You must have FabricPath enabled on the devices.
You must make these configurations on each switch that you want to participate in the FabricPath network.


If you are using additional, nondefault FabricPath topologies, you must create those topologies and assign the FP VLANs and interfaces to the specified topology.

For information on setting the FabricPath port mode, see the Cisco DCNM Interfaces Configuration Guide and for information on setting the FabricPath VLANs, see the Cisco DCNM Layer 2 Switching Configuration Guide.

This section describes how to configure additional FabricPath topologies and includes the following topics:

Configuring Additional Nondefault Topologies on One Device (Optional)

Configuring Additional Topologies on Multiple Devices Using the FabricPath Wizard (Optional)

Configuring Additional Nondefault Topologies on One Device (Optional)

You can configure additional nondefault FabricPath topologies on a selected device. You can also remove VLANs from selected topologies.


Note Ensure FabricPath VLANs are created before creating FabricPath topologies. For more information on creating VLANs, see Cisco DCNM Layer 2 Switching Configuration Guide.


BEFORE YOU BEGIN

Ensure that you have enabled FabricPath.

Ensure that you are working on the N7K-F132XP-15 module.

DETAILED STEPS


Step 1 From the Feature Selector pane, choose Switching > Fabricpath > Fabricpath Topology to open the Topology pane.

Step 2 From the Contents pane, in the Summary pane, click the device in which you want to configure additional nondefault topologies.

The system highlights the device in the Summary pane, and the Events tab appears.

Step 3 From the menu bar, choose New Fabricpath Topology > Current Device to create an additional nondefault topology in the selected device.

A line appears in the Summary table under the device you have selected

Step 4 Enter the number of the number of the new topology.

Step 5 In the VLANs column of the Summary table, click the arrow at the end of the row.

A pop-up box appears.

Step 6 In the pop-up box, enter the VLAN(s) that you want added to this topology.

Beginning with Cisco Release 5.2(1), the pop-up box also displays the configured mode for each VLAN, either Classical Ethernet (CE) or FabricPath.

Step 7 From the contents pane, in the summary pane, right-click the device you want to delete and click Delete.

Step 8 (Optional) From the menu bar, choose File > Deploy to apply your changes to the device.


Configuring Additional Topologies on Multiple Devices Using the FabricPath Wizard (Optional)

You configure additional nondefault FabricPath topologies on multiple devices using the FabricPath Topology Creation Wizard.

BEFORE YOU BEGIN

Ensure that FabricPath feature-set is installed and the VDCs are in the FabricPath feature-set allowed state.

Ensure that you are working on the N7K-F132XP-15 module.

DETAILED STEPS


Step 1 From the Feature Selector pane, choose Switching > Fabricpath > Fabricpath Topology to open the Topology pane.

Step 2 From the menu bar, choose New Fabricpath Topology > Multiple Device to create an additional nondefault topology in the selected device.

The Fabricpath Topology Creation Wizard opens and displays Step 1 of 5: Select Topology ID, VLANs & Devices.

Step 3 In the Topology ID field, enter the value for this topology.

Step 4 In the VLANs field enter the VLAN(s) that you want added to this topology.

The VLANs will be created in the device if not present.


Note All the VLANs you select for the topology are automatically changed to become FP-mode VLANs.


Step 5 In the Available Devices field, select the devices you want to include in this topology and click Add.

You can include all the devices by clicking Add All.


Note The Remove button allows you to change the devices added before you reach the Fabricpath Topology Configuration Overview pane.


Step 6 Check the Fabricpath IS-IS will decide Root Switch checkbox if you want the root automatically elected.

This is the IS-IS route on Layer 2.

Step 7 Click Next.

The Step 2 of 5: Select Fabricpath Physical Links pane appears.


Note All the interfaces you select are automatically configured as FabricPath ports upon selection, if you did not configure them previously.


Step 8 To select physical links, click the Physical Links button.

a. In the Available Interfaces field, select the links you want to include in this topology.

b. Click Add.


Note The Delete button allows you to change the interfaces added before you reach the Fabricpath Topology Configuration Overview pane.


Step 9 To select interfaces, click the Interfaces button.

A table appears in the Available Interfaces field listing the available devices and their interfaces, the mode for the interface, and the topologies to which that interface already belongs.

a. In the Available Interfaces field, select the Interfaces you want to include in this topology.

b. Click Add.

Step 10 To complete the topology setup with out modifying any IS-IS configurations, check the Skip IS-IS Authentication & Basic Configurations checkbox.

If you check this, go directly to Step 16.

Step 11 Click Next.

The Step 3 of 5: Fabricpath IS-IS Authentication Configurations pane appears.

Step 12 (Optional) The Existing Authentication Setting table will display all the existing IS-IS Authentication setting for each device. To change the authentication setting:

a. Check the Authentication Check checkbox to set to enable authentication check.

b. In the type field, click on the pull-down arrow to choose one of the following:

None

Text Authentication

Md5 Authentication

c. In the Keychain field, click the pull-down arrow and choose one of the following:

KeyChain Name

Key String

Encryption Type


Note Keychain field is enabled only if the devices configured are licensed devices.


Step 13 To complete the topology setup with out modifying any IS-IS basic configurations, check the Skip IS-IS Basic Configurations checkbox.

If you check this, go directly to Step 16.

Step 14 Click Next.

The Step 4 of 5: Fabricpath IS-IS Basic Configuration (Optional) pane appears.

Step 15 (Optional) If you want to change the default configuration for any of the Fabricpath IS-IS Process or Interfaces settings, enter the information.

Step 16 Click Next.

The Step 5 of 5: Fabricpath Topology Configuration Overview pane appears that displays information on the Fabricpath Topology that you configured.


Note If you want to change any of the configurations, click the Back button until you reach the page with the configuration you wish to change. Change the information and click through the screens to again display the topology information.


Step 17 Click Finish.

The Fabricpath Topology Configuration Deployment Status window displays the progress of the Fabricpath Topology configuration with a status bar and a checklist that appears as checked once the system completes each of the four configuration tasks.

If the system cannot configure a step of the task, a cross appears next to that task, and the system displays an error message.

Step 18 Click Done.


Displaying Information about the FabricPath Network

See the Cisco DCNM Fundamentals Configuration Guide for more information on viewing topology information for the FabricPath network.

You can display information about the FabricPath network.

This section covers the following topics:

Displaying Basic FabricPath Network Information

Displaying FabricPath Interface Network Information

Displaying Reachability Information

Displaying Basic FabricPath Network Information

BEFORE YOU BEGIN

Ensure that you have enabled FabricPath.

DETAILED STEPS


Step 1 From the Feature Selector pane, choose Switching > Fabricpath > Fabricpath Topology to open the Topology pane.

Step 2 From the Contents pane, in the Summary pane, click the device for which you want to view basic FabricPath network information.

Step 3 Click the + sign in front of the device to expand the pane and display the FabricPath networks to which the device belongs.

The system highlights the topology in the Summary pane, and tabs appear in the Details pane.

Step 4 In the Details pane, click the Fabricpath Topology Details tab.

Step 5 Click the Basic Settings section.

The system displays the FabricPath topology ID you are viewing, the VLANs in that FabricPath topology, and the status of that topology.


Displaying FabricPath Interface Network Information

You can view FabricPath interface network information.

BEFORE YOU BEGIN

Ensure that you have enabled FabricPath.

DETAILED STEPS


Step 1 From the Feature Selector pane, choose Switching > Fabricpath > Fabricpath Topology to open the Topology pane.

Step 2 From the Contents pane, in the Summary pane, click the device for which you want to view basic FabricPath network information.

Step 3 Click the + sign in front of the device to expand the pane and display the FabricPath networks to which the device belongs.

The system highlights the topology in the Summary pane, and tabs appear in the Details pane.

Step 4 In the Details pane, click the Fabricpath Topology Details tab.

Step 5 Click the Interface Settings section.

The system displays the information on both the local and neighboring FabricPath interfaces that belong to that FabricPath topology.


Displaying Reachability Information

You can gather the latest reachability information and view it for the FabricPath network.

BEFORE YOU BEGIN

Ensure that you have enabled FabricPath.

DETAILED STEPS


Step 1 From the Feature Selector pane, choose Switching > Fabricpath > Fabricpath Topology to open the Topology pane.

Step 2 From the Contents pane, in the Summary pane, click the device for which you want to view basic FabricPath network information.

Step 3 Click the + sign in front of the device to expand the pane and display the FabricPath networks to which the device belongs.

The system highlights the topology in the Summary pane, and tabs appear in the Details pane.

Step 4 In the Details pane, click the Reachability Status tab.

Step 5 Click the Reachability Status section.

The system displays information on the last time information was gathered and the devices that belong to the FabricPath topology along with their status.

Step 6 To gather current reachability status for the FabricPath network, click the Fetch button.


Field Descriptions for FabricPath Forwarding Information

These field descriptions are used for configuring optional additional FabricPath topologies and displaying information about the FabricPath Network. This section includes the following topics:

Fabricpath Topology: Fabricpath Topology Details: Basic Settings Section

Fabricpath Topology: Fabricpath Topology Details: Interface Settings Section

Fabricpath Topology: Reachability Status: Reachability Status Section

Fabricpath Topology: Fabricpath Topology Details: Basic Settings Section

Table 5-1 Fabricpath Topology: Fabricpath Topology Details: Basic Settings Section 

Field
Description

Topology ID

Display only. ID number of topology.

VLANs

VLANs in FabricPath topology.

State

Display only. State of FabricPath device in the network. The following are the options:

Up

Down


Fabricpath Topology: Fabricpath Topology Details: Interface Settings Section

Table 5-2 Fabricpath Topology: Fabricpath Topology Details: Interface Settings Section 

Field
Description
Local

Interface

Display only. All of the FabricPath interfaces of the FabricPath network in the device. Can be Ethernet or port-channel interface.

Topo. Status

Display only. Displays the interface status. The following are the options:

Up

Down

Adj. Status

Display only. Displays the FabricPath Layer 2 IS-IS adjacency status for the interface. The following are the options:

Up

Down

Oper. Status

Display only. Displays the operational status of the interface. The following are the options:

Up

Down

Neighbor Status

Topo. Status

Display only. Displays the interface status. The following are the options:

Up

Down

Adj. Status

Display only. Displays the FabricPath Layer 2 IS-IS adjacency status for the interface. The following are the options:

Up

Down

Oper. Status

Display only. Displays the operational status of the interface. The following are the options:

Up

Down


Fabricpath Topology: Reachability Status: Reachability Status Section

Table 5-3 Fabricpath Topology: Reachability Status: Reachability Status Section 

Field
Description

Last Fetch Time

Display only. Displays the last time this information was gathered, down to the second.

Status

Display only. Displays the status for all devices in the FabricPath network. The following are the choices:

Reachable

Unreachable


Feature History for Configuring FabricPath Using the DCNM

Table 5-4 lists the release history for this feature.

Table 5-4 Feature History for FabricPath

Feature Name
Releases
Feature Information

FabricPath

5.1(1)

These features were introduced.

Additional FabricPath topologies

5.2(1)

These features were introduced.