This section provides a detailed explanation
of how to configure peer routing in a VLT domain.
In the following example, devices are configured as
follows:
Access switch A1 is connected to two VLT peers (Dell-1
and Dell-2).
The two VLT peers are connected to an upstream switch
R1.
OSPF is configured in Dell-1, Dell-2, and R1 switches.
Dell-1 is configured as the root bridge.
Dell-1 is configured as the VLT primary.
As the Router ID of Dell-1 is the highest in the topology
(highest loopback address of 172.17.1.1), Dell-1 is the OSPF Designated
Router.
As the Router ID of Dell-2 is the second highest in
the topology (172.16.1.1), Dell-2 is the OSPF Backup Designated Router.
Figure 1. Peer Routing
Configuration Example
Dell-1 Switch
Configuration
In the following output, RSTP is enabled with a bridge
priority of 0. This ensures that Dell-1 becomes the root bridge.
DellEMC#1#show run | find protocol
protocol spanning-tree pvst
no disable
vlan 1,20,800,900 bridge-priority 0
The following output shows the existing VLANs.
DellEMC#1#show vlan | find NUM
NUM Status Description Q Ports
* 1 Active U Po10 (Te 0/0-1)
U Te 0/4,47
20 Active OSPF PEERING VLAN U Po1 (Te 0/6)
V Po10 (Te 0/0-1)
800 Active Client-VLAN V Po10 (Te 0/0-1)
900 Active Client-VLAN-2 V Po10 (Te 0/0-1)
The following is the configuration in interfaces:
DellEMC#1#sh run int ma0/0
interface ManagementEthernet 0/0
description Used_for_VLT_Keepalive
ip address 10.10.10.1/24
no shutdown
(The management interfaces are part of a default VRF
and are isolated from the switch’s data plane.) In Dell-1, te 0/0
and te 0/1 are used for VLTi.
DellEMC#1#sh run int te0/0
interface TenGigabitEthernet 0/0
description VLTi LINK
no ip address
no shutdown
(VLTi Physical link)
!
DellEMC#1#sh run int te0/1
interface TenGigabitEthernet 0/1
description VLTi LINK
no ip address
no shutdown
(VLTi Physical link)
The following example shows that te 0/0 and te 0/1 are included
in port channel 10. Also note that configuration on the VLTi links
does not contain the switchport command.
DellEMC#1#sh run int po10
interface Port-channel 10
description VLTi Port-Channel
no ip address
channel-member TenGigabitEthernet 0/0-1
no shutdown
Te 0/4 connects
to the access switch A1.
DellEMC#1#sh run int te0/4
interface TenGigabitEthernet 0/4
description To_Access_Switch_A1_fa0/13
no ip address
port-channel-protocol LACP
port-channel 2 mode active
no shutdown
Te 0/6 connects to
the uplink switch R1.
DellEMC#1#sh run int te0/6
interface TenGigabitEthernet 0/6
description To_CR1_fa0/13
no ip address
port-channel-protocol LACP
port-channel 1 mode active
no shutdown
Port channel 1 connects the uplink switch R1.
DellEMC#1#sh run int po1
interface Port-channel 1
description port-channel_to_R1
no ip address
switchport
vlt-peer-lag port-channel 1
no shutdown
Port channel 2 connects the access switch A1.
DellEMC#1#sh run int po2
interface Port-channel 2
description port-channel_to_access_switch_A1
no ip address
portmode hybrid
switchport
vlt-peer-lag port-channel 2
no shutdown
Vlan 20 is used in Dell-1, Dell-2, and R1 to form
OSPF adjacency. When OSPF is converged, the routing tables in all
devices are synchronized.
DellEMC#1#sh run int vlan 20
interface Vlan 20
description OSPF PEERING VLAN
ip address 192.168.20.1/29
untagged Port-channel 1
no shutdown
!
DellEMC#1#sh run int vlan 800
interface Vlan 800
description Client-VLAN
ip address 192.168.8.1/24
tagged Port-channel 2
no shutdown
The following output shows Dell-1 is configured with
VLT domain 1. The peer-link port-channel command
makes port channel 10 as the VLTi link. The peer-routing command enables
peer routing between VLT peers in VLT domain 1. The IP address configured
with the backup-destination command is the management IP address of
the VLT peer (Dell-2).
DellEMC#1#sh vlt brief
VLT Domain Brief
------------------
Domain ID: 1
Role: Primary
Role Priority: 4096
ICL Link Status: Up
HeartBeat Status: Up
VLT Peer Status: Up
Local Unit Id: 0
Version: 6(3)
Local System MAC address: 90:b1:1c:f4:2c:bb
Remote System MAC address: 90:b1:1c:f4:29:f1
Configured System MAC address: 90:b1:1c:f4:01:01
Remote system version: 6(3)
Delay-Restore timer: 90 seconds
Peer routing : Enabled
Peer routing-Timeout timer: 0 seconds
Multicast peer routing timeout: 150 seconds
Verify that the heartbeat mechanism is operational
Use the show vlt detail command to
verify that VLT is functional and that the correct VLANs are allowed.
DellEMC#1#sh vlt detail
Local LAG Id Peer LAG Id Local Status Peer Status Active VLANs
------------ ----------- ------------ ----------- -------------
1 1 UP UP 20
2 2 UP UP 1, 800, 900
The following output displays the OSPF configuration
in Dell-1
DellEMC#1#sh run | find router
router ospf 1
router-id 172.17.1.1
network 192.168.9.0/24 area 0
network 192.168.8.0/24 area 0
network 172.17.1.0/24 area 0
network 192.168.20.0/29 area 0
passive-interface default
no passive-interface vlan 20
While the passive-interface default command prevents all interfaces from establishing an OSPF neighborship,
the no passive-interface vlan 20 command enables
the interface for VLAN 20, the OSPF peering VLAN, to establish OSPF
adjacencies.
The following output displays that Dell-1 forms neighborship
with Dell-2 and R1.
DellEMC#1#show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface Area
172.16.1.2 1 FULL/BDR 00:00:31 192.168.20.2 Vl 20 0
172.15.1.1 1 FULL/DROTHER 00:00:39 192.168.20.3 Vl 20 0
The following output displays the routes learned using
OSPF.
DellEMC#1#show ip route ospf
Destination Gateway Dist/Metric Last Change
----------- ------- ----------- -----------
O 2.2.2.2/24 via 192.168.20.3, Vl 20 110/2 02:13:50
O 3.3.3.2/24 via 192.168.20.3, Vl 20 110/2 02:13:50
O 4.4.4.2/24 via 192.168.20.3, Vl 20 110/2 02:13:50
O 172.15.1.1/32 via 192.168.20.3, Vl 20 110/2 02:13:50
O 172.16.1.2/32 via 192.168.20.2, Vl 20 110/1 02:13:50
The following output displays the MAC address of all
interfaces in the system. All interfaces, physical and virtual, have
the same MAC address. This is the address used for peer routing.
DellEMC#1#show interfaces | grep Hardware
Hardware is DellEMCEth, address is 90:b1:1c:f4:2c:bd
Hardware is DellEMCEth, address is 90:b1:1c:f4:2c:bd
Hardware is DellEMCEth, address is 90:b1:1c:f4:2c:bd
Hardware is DellEMCEth, address is 90:b1:1c:f4:2c:bd
! Output truncated for brevity
Verify if peer routing has populated the CAM table
with the correct information using the show cam mac command.
DellEMC#1#sh cam mac stack-unit 0 port-set 0
!
VlanId Mac Address Region Interface
20 90:b1:1c:f4:29:f3 STATIC Po 10
20 00:0d:bc:6e:93:00 DYNAMIC Po 1
20 ff:ff:ff:ff:ff:ff STATIC 00001
900 90:b1:1c:f4:29:f3 STATIC Po 10
900 ff:ff:ff:ff:ff:ff STATIC 00001
800 90:b1:1c:f4:29:f3 STATIC Po 10
800 ff:ff:ff:ff:ff:ff STATIC 00001
0 ff:ff:ff:ff:ff:ff STATIC 00001
0 90:b1:1c:f4:2c:bd LOCAL_DA 00001
0 90:b1:1c:f4:29:f3 LOCAL_DA 00001A
The above output shows that the 90:b1:1c:f4:2c:bd
MAC address belongs to Dell-1. The 90:b1:1c:f4:29:f3 MAC address belongs
to Dell-2. Also note that these MAC addresses are marked with LOCAL_DA.
This means, these are the local destination MAC addresses used by
hosts when routing is required. Packets sent to this MAC address are
directly forwarded to their destinations without being sent to the
peer switch.
Dell-2 Switch
Configuration
In the following output, RSTP is enabled with a bridge
priority of 32768, which is the second lowest in this topology. This
ensures that Dell-2 becomes the root bridge if Dell-1 fails.
DellEMC#2#sh run | find protocol
protocol spanning-tree pvst
no disable
vlan 1,20,800,900 bridge-priority 32768
The following output shows the existing VLANs.
DellEMC#1#show vlan | find NUM
NUM Status Description Q Ports
* 1 Active U Po10 (Te 0/0-1)
20 Active OSPF PEERING VLAN U Po1 (Te 0/6)
V Po10 (Te 0/0-1)
800 Active Client-VLAN V Po10 (Te 0/0-1)
U Te 0/4
900 Active Client-VLAN-2 V Po10 (Te 0/0-1)
Configuration on Interfaces
DellEMC#2#sh run int ma0/0
interface ManagementEthernet 0/0
description Used_for_VLT_Keepalive
ip address 10.10.10.2/24
no shutdown
In Dell-2,
te 0/0 and te 0/1 are used for VLTi.
In Dell-2,
tw 1/1 and tw 1/2 are used for VLTi.
DellEMC#2#sh run int te0/0
interface TenGigabitEthernet 0/0
description VLTi LINK
no ip address
no shutdown
!
DellEMC#1#sh run int te0/1
interface TenGigabitEthernet 0/1
description VLTi LINK
no ip address
no shutdown
The following example shows that te 0/0 and te 0/1
are included in port channel 10. Also note that configuration on the
VLTi links does not contain the switchport command.
Dell-2#sh run int po10
interface Port-channel 10
description VLTi Port-Channel
no ip address
channel-member TenGigabitEthernet 0/0-1
no shutdown
Te 0/4
connects to the access switch A1.
Dell-2#sh run int te0/4
interface TenGigabitEthernet 0/4
description To_Access_Switch_A1_fa0/13
no ip address
port-channel-protocol LACP
port-channel 2 mode active
no shutdown
Te 0/6
connects to the uplink switch R1.
Dell-2#sh run int te0/6
interface TenGigabitEthernet 0/6
description To_CR1_fa0/13
no ip address
port-channel-protocol LACP
port-channel 1 mode active
no shutdown
Port channel 1 connects the uplink switch R1.
Dell-2#sh run int po1
interface Port-channel 1
description port-channel_to_R1
no ip address
switchport
vlt-peer-lag port-channel 1
no shutdown
Port channel 2 connects the access switch A1.
Dell-2#sh run int po2
interface Port-channel 2
description port-channel_to_access_switch_A1
no ip address
portmode hybrid
switchport
vlt-peer-lag port-channel 2
no shutdown
Vlan 20 is used in Dell-1, Dell-2, and R1 to form
OSPF adjacency. When OSPF is converged, the routing tables in all
devices are synchronized.
Dell-2#sh run int vlan 20
interface Vlan 20
description OSPF PEERING VLAN
ip address 192.168.20.2/29
untagged Port-channel 1
no shutdown
!
Dell-2#sh run int vlan 800
interface Vlan 800
description Client-VLAN
ip address 192.168.8.2/24
tagged Port-channel 2
no shutdown
The following output shows Dell-2 is configured with
VLT domain 1. The peer-link port-channel command makes port channel
10 as the VLTi link. The peer-routing command enables
peer routing between VLT peers in VLT domain 1. The IP address configured
with the backup-destination command is the management IP address of
the VLT peer (Dell-1). A priority value of 55000 makes Dell-2 as the
secondary VLT peer.
Dell-2#sh vlt brief
VLT Domain Brief
------------------
Domain ID: 1
Role: Secondary
Role Priority: 55000
ICL Link Status: Up
HeartBeat Status: Up
VLT Peer Status: Up
Local Unit Id: 1
Version: 6(3)
Local System MAC address: 90:b1:1c:f4:29:f1
Remote System MAC address: 90:b1:1c:f4:2c:bb
Configured System MAC address: 90:b1:1c:f4:01:01
Remote system version: 6(3)
Delay-Restore timer: 90 seconds
Peer routing : Enabled
Peer routing-Timeout timer: 0 seconds
Multicast peer routing timeout: 150 seconds
Verify if the heartbeat mechanism is operational on
Dell-2
Use the show vlt detail command to verify that VLT
is functional and that the correct VLANs are allowed.
Dell-2#sh vlt detail
Local LAG Id Peer LAG Id Local Status Peer Status Active VLANs
------------ ----------- ------------ ----------- -------------
1 1 UP UP 20
2 2 UP UP 1, 800, 900
The following output displays the OSPF configuration
in Dell-2
Dell-2#sh run | find router
router ospf 1
router-id 172.17.1.2
network 192.168.8.0/24 area 0
network 192.168.9.0/24 area 0
network 172.16.1.0/24 area 0
network 192.168.20.0/29 area 0
passive-interface default
no passive-interface vlan 20
While the passive-interface default command prevents
all interfaces from establishing an OSPF neighborship, the no passive-interface
vlan 20 command allows the interface for VLAN 20, the OSPF peering
VLAN, to establish OSPF adjacencies.
The following output displays that Dell-1 forms neighborship
with Dell-2 and R1.
Dell-2#show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface Area
172.17.1.1 1 FULL/DR 00:00:31 192.168.20.1 Vl 20 0
172.15.1.1 1 FULL/DROTHER 00:00:33 192.168.20.3 Vl 20 0
The following output displays the routes learned using
OSPF. Dell-2 also learns the routes to the loopback addresses on R1
through OSPF.
Dell-2#show ip route ospf
Destination Gateway Dist/Metric Last Change
----------- ------- ----------- -----------
O 2.2.2.2/24 via 192.168.20.3, Vl 20 110/2 02:15:25
O 3.3.3.2/24 via 192.168.20.3, Vl 20 110/2 02:15:25
O 4.4.4.2/24 via 192.168.20.3, Vl 20 110/2 02:15:25
O 172.15.1.1/32 via 192.168.20.3, Vl 20 110/2 02:15:25
O 172.16.1.2/32 via 192.168.20.1, Vl 20 110/1 02:15:25
The following output displays the MAC address of all
interfaces in the system. All interfaces, physical and virtual, have
the same MAC address. This is the address used for peer routing.
DellEMC#2#show interfaces | grep Hardware
Hardware is DellEMCEth, address is 90:b1:1c:f4:29:f3
Hardware is DellEMCEth, address is 90:b1:1c:f4:29:f3
Hardware is DellEMCEth, address is 90:b1:1c:f4:29:f3
Hardware is DellEMCEth, address is 90:b1:1c:f4:29:f3
(Output truncated for brevity)
Verify if peer routing has populated the CAM table
with the correct information using the show cam mac command.
DellEMC#2#sh cam mac stack-unit 0 port-set 0
VlanId Mac Address Region Interface
20 90:b1:1c:f4:29:f3 STATIC Po 10
20 00:0d:bc:6e:93:00 DYNAMIC Po 1
20 ff:ff:ff:ff:ff:ff STATIC 00001
900 90:b1:1c:f4:29:f3 STATIC Po 10
900 ff:ff:ff:ff:ff:ff STATIC 00001
800 90:b1:1c:f4:29:f3 STATIC Po 10
800 ff:ff:ff:ff:ff:ff STATIC 00001
0 ff:ff:ff:ff:ff:ff STATIC 00001
0 90:b1:1c:f4:2c:bd LOCAL_DA 00001
0 90:b1:1c:f4:29:f3 LOCAL_DA 00001
The MAC addresses of the VLAN interfaces of both VLT
peers are registered in the L2 CAM as LOCAL_DA addresses.
R1 Configuration
Configuration on Interfaces
R1#show run | find Loopback2
interface Loopback2
ip address 2.2.2.2 255.255.255.0
!
interface Loopback3
ip address 3.3.3.2 255.255.255.0
!
interface Loopback4
ip address 4.4.4.2 255.255.255.0
R1#show run int port-channel 1
interface Port-channel1
switchport
ip address 192.168.20.3 255.255.255.248
R1#show run | find router
router ospf 1
router-id 172.15.1.1
passive-interface default
no passive-interface Port-channel1
network 2.2.2.0 0.0.0.255 area 0
network 3.3.3.0 0.0.0.255 area 0
network 4.4.4.0 0.0.0.255 area 0
(The above subnets correspond to loopback interfaces lo2, lo3 and lo4. These three loopback interfaces are advertised to the VLT pair, DellEMC#1 and DellEMC#2)
network 172.15.1.0 0.0.0.255 area 0
network 192.168.20.0 0.0.0.7 area 0
CR1#show ip ospf neighbor
(R1 is a DROTHER)
Neighbor ID Pri State Dead Time Address Interface
172.16.1.2 1 FULL/BDR 00:00:31 192.168.20.2 Port-channel1
172.17.1.1 1 FULL/DR 00:00:38 192.168.20.1 Port-channel1
CR1#show ip route
(Output Truncated)
2.0.0.0/24 is subnetted, 1 subnets
C 2.2.2.0 is directly connected, Loopback2
3.0.0.0/24 is subnetted, 1 subnets
C 3.3.3.0 is directly connected, Loopback3
O 192.168.8.0/24 [110/2] via 192.168.20.2, 02:02:34, Port-channel1
[110/2] via 192.168.20.1, 02:02:34, Port-channel1
(OSPF-learned route back to client subnet – VLAN 800)
4.0.0.0/24 is subnetted, 1 subnets
C 4.4.4.0 is directly connected, Loopback4
O 192.168.9.0/24 [110/2] via 192.168.20.2, 02:02:34, Port-channel1
[110/2] via 192.168.20.1, 02:02:34, Port-channel1
(OSPF-learned route back to client subnet #2 – VLAN 900)
172.17.0.0/24 is subnetted, 1 subnets
O 172.17.1.1 [110/1] via 192.168.20.1, 02:02:34, Port-channel1
172.16.0.0/24 is subnetted, 1 subnets
O 172.16.1.2 [110/1] via 192.168.20.2, 02:02:34, Port-channel1
192.168.20.0/29 is subnetted, 1 subnets
C 192.168.20.0 is directly connected, Port-channel1
(OSPF peering VLAN)
10.0.0.0/24 is subnetted, 1 subnets
C 10.10.10.0 is directly connected, FastEthernet0/2
Access Switch
A1 Configurations and Verification
A1 access switch is configured to not be the STP root
bridge
A1#sh run | be spanning
spanning-tree mode pvst
spanning-tree vlan 1,800,900 priority 61440
This default route is configured for testing purposes,
as described in the next section. The access switch (A1) is used to
generate ICMP test PINGs to a loopback interface on CR1. This default
route points to DellEMC#2’s VLAN 800 SVI interface. It’s in place
to ensure that routed test traffic has DellEMC#2’s MAC address as
the destination address in the Ethernet frame’s header
When A1 sends a packet to R1, the VLT peers act as
the default gateway for each other. If the packet reaches Dell-1,
irrespective of the default gateway used, Dell-1 routes the packet
to R1. Similarly, if the packet reaches Dell-2, irrespective of the
default gateway used, Dell-2 routes the packet to R1.
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