CH A P T E R
39
Layer 2 over Multipoint GRE (L2omGRE)
Note
•
Prerequisites for L2omGRE, page 39-1
•
Restrictions for L2omGRE, page 39-2
•
Information About L2omGRE, page 39-2
•
Default Settings for L2omGRE, page 39-3
•
How to Configure L2omGRE, page 39-3
•
Verifying the L2omGRE Configuration, page 39-5
•
For complete syntax and usage information for the commands used in this chapter, see these
publications:
http://www.cisco.com/en/US/products/ps9536/prod_command_reference_list.html
•
Tip
Cisco IOS Release 12.2SY supports only Ethernet interfaces. Cisco IOS Release 12.2SY does not
support any WAN features or commands.
For additional information about Cisco Catalyst 6500 Series Switches (including configuration examples
and troubleshooting information), see the documents listed on this page:
http://www.cisco.com/en/US/products/hw/switches/ps708/tsd_products_support_series_home.html
Participate in the Technical Documentation Ideas forum
Prerequisites for L2omGRE
None.
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Restrictions for L2omGRE
Restrictions for L2omGRE
•
The L2omGRE feature is supported in VSS mode.
•
The VLAN interface used to support L2omGRE cannot also be configured to support any Layer 3
features.
•
You can configure QoS to police (rate limit) Layer 2 traffic that is flooded in a VLAN because it is
addressed to a currently unlearned MAC-Layer destination address (see match l2 miss in the
“Traffic Classification” section on page 60-2).
Information About L2omGRE
The L2omGRE feature provides Layer 2 connectivity between multiple separate network sites by
extending the topology of a Layer 2 broadcast domain through an mGRE tunnel (see Figure 39-1).
Figure 39-1
L2omGRE Topology
Local VLANs
Local VLANs
Catalyst 6500
Switch One
Catalyst 6500
Switch Two
Tunneled VLANs
Tunneled VLANs
mGRE Tunnels
Tunneled VLANs
Local VLANs
330528
Catalyst 6500
Switch Three
The L2omGRE feature associates a VLAN interface with an mGRE tunnel interface. mGRE tunnel
interfaces configured to support the L2omGRE feature function like Layer 2 LAN ports to provide
Layer 2 switching (bridging) for traffic of all types in the VLAN, so that the tunnel only carries traffic
addressed to devices accessible through the mGRE tunnel (see the “Information about Layer 2 Ethernet
Switching” section on page 18-2). The switch will learn MAC addresses that are accessible through
mGRE tunnels and the show mac address-table command displays the learned addresses.
The PFC and any DFCs support bridging and mGRE tunnel encapsulation and decapsulation in
hardware.
Each tunnel can carry multiple L2omGRE-connected VLANs. The tunnel encapsulation includes the
VLAN ID. When the tunneled traffic is decapsulated, the VLAN ID in the tunneled traffic is used to
select the correct VLAN for the traffic.
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Default Settings for L2omGRE
Default Settings for L2omGRE
None.
How to Configure L2omGRE
•
Configuring a Loopback Interface, page 39-3
•
Configuring an mGRE Tunnel Interface, page 39-3
•
Configuring a VLAN Interface, page 39-4
•
L2omGRE Configuration Examples, page 39-5
Configuring a Loopback Interface
To configure a loopback inteface to support L2omGRE, perform this task:
Command or Action
Purpose
Step 1
Router> enable
Enables privileged EXEC mode. Enter your password if
prompted.
Step 2
Router# configure terminal
Enters global configuration mode.
Step 3
Router(config)# interface loopback number
Creates the loopback interface and enters interface
configuration mode.
Step 4
Router(config-if)# ip address address mask
Configures an IP address on the interface.
Note
Step 5
Router(config-if)# end
Tunnel interfaces on other switches refer to this IP
address on this switch.
Returns to global configuration mode.
Configuring an mGRE Tunnel Interface
To configure an mGRE tunnel inteface, perform this task:
Step 1
Command or Action
Purpose
Router(config)# interface tunnel number
Creates a tunnel interface and enters interface
configuration mode.
Note
Step 2
Router(config-if)# ip address address mask
VLAN interfaces on this switch refer to this
tunnel number.
Configures an IP address on the interface.
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How to Configure L2omGRE
Step 3
Command or Action
Purpose
Router(config-if)# ip nhrp map tunnel_address
loopback_address
Configures the IP-to-nonbroadcast multiaccess (NBMA)
address mapping to the loopback interface IP addresses
configured on the other switches with L2omGRE tunnel
interfaces.
•
Enter the tunnel_address loopback_address values
configured on the other L2omGRE switches.
•
Repeat this command for each of the other
L2omGRE switches.
Step 4
Router(config-if)# ip nhrp network-id ID
Enables the Next Hop Resolution Protocol (NHRP) for
the mGRE tunnels. Use the same ID value on all of the
L2omGRE tunnel interfaces.
Step 5
Router(config-if)# tunnel source loopback number
Associates this tunnel interface with the loopback
interface.
Step 6
Router(config-if)# tunnel mode gre multipoint
Configures multipoint GRE as the tunnel mode.
Step 7
Router(config-if)# end
Returns to global configuration mode.
Configuring a VLAN Interface
To configure a VLAN interface to support L2omGRE, perform this task:
Command or Action
Purpose
Step 1
Router(config)# interface vlan number
Creates the VLAN interface and enters interface
configuration mode.
Step 2
Router(config-if)# no ip address
Ensures that no IP address is configured on the interface.
Step 3
Router(config-if)# platform xconnect l2gre
tunnel number
Associates the VLAN interface with an L2omGRE tunnel
interface.
Step 4
Router(config-if)# end
Returns to global configuration mode.
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Verifying the L2omGRE Configuration
L2omGRE Configuration Examples
The L2omGRE configuration commands must be coordinated as follows:
•
The ip nhrp map commands on each switch point to the tunnel and loopback IP addresses on each
of the other switches.
•
On each switch, the tunnel source loopback command points to the loopback interface configured
on that switch.
•
On each switch, the platform xconnect l2gre tunnel command points to the L2omGRE tunnel
interface on that switch.
Enter the show platform l2transport gre summary command to display information about the
L2omGRE configuration on a switch.
Switch One
Switch Two
Switch Three
interface loopback 1
interface loopback 1
interface loopback 1
ip address 10.3.3.3 255.255.255.255
ip address 10.2.2.2 255.255.255.255
ip address 10.1.1.1 255.255.255.255
interface tunnel 10
interface tunnel 10
interface tunnel 10
ip address 10.30.30.3 255.255.255.0
ip address 10.20.20.2 255.255.255.0
ip address 10.10.10.1 255.255.255.0
no ip redirects
no ip redirects
no ip redirects
ip nhrp map 10.10.10.1 10.1.1.1
ip nhrp map 10.10.10.1 10.1.1.1
ip nhrp map 10.20.20.2 10.2.2.2
ip nhrp map 10.20.20.2 10.2.2.2
ip nhrp map 10.30.30.3 10.3.3.3
ip nhrp map 10.30.30.3 10.3.3.3
ip nhrp network-id 10
ip nhrp network-id 10
ip nhrp network-id 10
tunnel source loopback1
tunnel source loopback 1
tunnel source loopback 1
tunnel mode gre multipoint
tunnel mode gre multipoint
tunnel mode gre multipoint
interface vlan 10
interface vlan 10
interface vlan 10
no ip address
no ip address
no ip address
platform xconnect l2gre tunnel 10
platform xconnect l2gre tunnel 10
platform xconnect l2gre tunnel 10
Verifying the L2omGRE Configuration
Enter the show platform l2transport gre command to display information about L2omGRE, including
traffic statistics.
Tip
For additional information about Cisco Catalyst 6500 Series Switches (including configuration examples
and troubleshooting information), see the documents listed on this page:
http://www.cisco.com/en/US/products/hw/switches/ps708/tsd_products_support_series_home.html
Participate in the Technical Documentation Ideas forum
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Layer 2 over Multipoint GRE (L2omGRE)