Appendix: Port-based split horizon

This chapter provides Port-Based Split Horizon configuration information.

Overview

Note:

Port-based split horizon is supported on all 7210 SAS platforms as described in this document, except the 7210 SAS-Mxp.

The port-based split horizon feature can be used to disable local switching on the 7210 SAS. A loop-free topology can be achieved using split horizon on 7210 SAS switches.

Traffic arriving on an access or a network port within a split horizon group will not be copied to other access and a network ports in the same split horizon group, but will be copied to an access or network ports in other split horizon groups.

Since split horizon is a per port feature in 7210 SAS, all SAPs associated with the port becomes part of split horizon group configured on that port.

Topology

The following figure shows an example of split horizon groups used to prevent communication between two access SAPs and between two network ports.

Figure 1. Split horizon group example

Using 7210 SAS-1 as an example:

  1. Split horizon group ‟access” is created to prevent any communication between the SAP part of port 1/1/4 and port 1/1/5 (configured as access port) within the same VPLS.

  2. Split horizon group ‟network” is created to prevent any communication between port 1/1/1 and port 1/1/3 (configured as a network port) within the same VPLS.

  3. VPLS 100 is created on 7210 SAS-1 with spoke-SDPs on network port 1/1/1 and 1/1/3, and SAPs on 1/1/4 and 1/1/5 as part of this VPLS. CE1, CE2 and CE3 are the customer sites.

  4. With this configuration, any communication between ports 1/1/4 and 1/1/5 gets blocked, similarly communication between ports 1/1/1 and 1/1/3 gets blocked but any traffic received on ports (for example, spoke-SDPs on these ports) that belong to split horizon group ‟network” will be switched to ports (for example, SAPs on these ports) that belong to split horizon group ‟access” and the other way around based on the FDB entries for VPLS 100.

Configuration guidelines

The following configuration guidelines must be followed to configure a split horizon group:

Note:

When configuring split horizon on a port, it must be configured before creating any SAPs associated with the port.

  1. Create a split horizon group in the config prompt. The group name must be unique across the system.

    7210-SAS1>config#info
#--------------------------------------------------
echo "Split-horizon-group Configuration"
#--------------------------------------------------
    split-horizon-group access create 
        description ‟Block access between access Ports”
    split-horizon-group network create
        description "Block access between network Ports"
    exit 
#-------------------------------------------------- 
7210-SAS1>config#

  2. Configure ports 1/1/4 and 1/1/5 as access ports and associate these ports with split horizon group ‟access”.

    7210-SAS1>config#info
#--------------------------------------------------
echo "Port Configuration"

#--------------------------------------------------
    port 1/1/4
        split-horizon-group access
        ethernet
            mode access 
            access
            exit
        exit
        no shutdown
    exit 
    port 1/1/5
        split-horizon-group access
        ethernet
            mode access 
            access
            exit
        exit
        no shutdown
     exit
#--------------------------------------------------
7210-SAS1>config#

  3. Configure ports 1/1/1 and 1/1/3 as network ports and associate these ports with split horizon group ‟network”. The default Ethernet encapsulation for network port is null.

    7210-SAS1>config# info
#--------------------------------------------------
echo "Port Configuration"

#--------------------------------------------------
    port 1/1/1
        split-horizon-group network
        ethernet
        exit
        no shutdown
exit 
    port 1/1/3
        split-horizon-group network
        ethernet
        exit
        no shutdown
  exit
#--------------------------------------------------
7210-SAS1>config#

  4. Create a VPLS instance 100.

    #--------------------------------------------------
echo "Service Configuration"
#--------------------------------------------------
    service
          customer 2 create
          exit
         vpls 100 customer 2 create
            stp
                shutdown
            exit
            sap 1/1/4 create
            exit
            sap 1/1/5 create
            exit
            spoke-sdp 1:1 create
            exit
            spoke-sdp 2:1 create
            exit
         no shutdown
    exit
...
#--------------------------------------------------

Verification

The following output verifies the split horizon configuration on a 7210 SAS.

7210-SAS1# show split-horizon-group 
===============================================================================
Port: Split Horizon Group
===============================================================================
Name                               Description                                 
-------------------------------------------------------------------------------
access                             Block access between access Ports
network                            Block access between network Ports
No. of Split Horizon Groups: 2
===============================================================================
7210-SAS1#

The following shows the command usage to verify the port association with split horizon groups:

7210-SAS1# show split-horizon-group access 
===============================================================================
Port: Split Horizon Group
===============================================================================
Name                               Description                                 
-------------------------------------------------------------------------------
access                             Block access between access Ports
-------------------------------------------------------------------------------
Associations
-------------------------------------------------------------------------------
Port1/1/4                          10/100/Gig Ethernet SFP                     
Port1/1/5                          10/100/Gig Ethernet SFP                     
 
Ports Associated : 2     
===============================================================================
7210-SAS1#


7210-SAS1# show split-horizon-group network
===============================================================================
Port: Split Horizon Group
===============================================================================
Name                               Description                                 
-------------------------------------------------------------------------------
network                           Block access between network Ports
-------------------------------------------------------------------------------
Associations
-------------------------------------------------------------------------------
Port1/1/1                          10/100/Gig Ethernet SFP                     
Port1/1/3                          10/100/Gig Ethernet SFP                     
 
Ports Associated : 2     
===============================================================================
7210-SAS1#