Dell Networking Extends Multipathing Capabilities with VLT Routing

Dell Networking recently released enhancements to their VLT multipathing technology in FTOS 9.2 now available on S4810, S4820T, and Z9000. For a quick primer on Dell’s VLT technology read my prior blog post here. The most noticeable enhancement is the support of layer 3 routing protocols over VLT. Additional enhancements include the ability of VLT peers to synchronize ARP entries learned from non-VLT interfaces, support for IPv6, and the ability to synchronize multicast routing tables between peer VLT ports. In this blog, I use 4 x Dell S4810s [FTOS 9.2] and 1 x Dell S60 (for a management switch) [FTOS 8.3.3.9] to demonstrate routed VLT.

Below is the network diagram for this lab.

Network Diagram for Routed VLT Lab

Network Diagram for Routed VLT Lab

As you can see VLT is configured on two S4810 switches (‘Dell_S4810_1’ and ‘Dell_S4810_2’) down to a third S4810 switch, ‘Dell_S4810_3’. I have configured OSPF on all four Dell S4810 switches and will demonstrate routing over VLT using OSPF.

Dell_S4810_4 Config:

– enable
– conf
– protocol spanning-tree rstp
– no disable
– bridge-priority 8192
– exit

– interface range tengigabitethernet 0/17 – 18
– switchport
– no shutdown
– exit

– interface vlan 30
– untagged tengigabitethernet 0/17
– untagged tengigabitethernet 0/18
– ip address 30.0.0.1/24
– no shutdown
– exit

– interface loopback 0
– ip address 40.0.0.1/24
– exit

– interface loopback 1
– ip address 50.0.0.1/24
– exit

– router ospf 1
– network 30.0.0.0/24 area 0
– network 40.0.0.0/24 area 0
– network 50.0.0.0/24 area 0
– end
– write

Dell_S4810_1 Config (VLT Peer):

– enable
– conf
– protocol spanning-tree rstp
– no disable
– bridge-priority 0
– exit

– interface managementethernet 0/0
– ip address 10.11.129.145/20
– no shutdown
– exit

– interface tengigabitethernet 0/17
– ip address 30.0.0.2/24
– no shutdown
– exit

– interface range tengigabitethernet 0/11 – 12
– no shutdown
– exit

– interface port-channel 100
– channel-member tengigabitethernet 0/11
– channel-member tengigabitethernet 0/12
– no shutdown
– exit

– vlt domain 100
– back-up destination 10.11.129.146
– peer-link port-channel 100
– primary-priority 1
– unit-id 0
– peer-routing timeout 10
– exit

– interface tengigabitethernet 0/15
– port-channel-protocol LACP
– port-channel 10 mode active
– no shutdown
– exit

– interface port-channel 10
– switchport
– vlt-peer-lag port-channel 10
– no shutdown
– exit

– interface vlan 10
– untagged port-channel 10
– ip address 10.0.0.2/24
– no shutdown
– exit

– router ospf 1
– network 10.0.0.0/24 area 0
– network 30.0.0.0/24 area 0
– end
– write

Dell_S4810_2 Config (VLT Peer):

– enable
– conf
– protocol spanning-tree rstp
– no disable
– bridge-priority 4096
– exit

– interface managementethernet 0/0
– ip address 10.11.129.146/20
– no shutdown
– exit

– interface tengigabitethernet 0/17
– ip address 30.0.0.3/24
– no shutdown
– exit

– interface range tengigabitethernet 0/11 – 12
– no shutdown
– exit

– interface port-channel 100
– channel-member tengigabitethernet 0/11
– channel-member tengigabitethernet 0/12
– no shutdown
– exit

– vlt domain 100
– back-up destination 10.11.129.145
– peer-link port-channel 100
– primary-priority 1
– unit-id 0
– peer-routing timeout 10
– exit

– interface tengigabitethernet 0/16
– port-channel-protocol LACP
– port-channel 10 mode active
– no shutdown
– exit

– interface port-channel 10
– switchport
– vlt-peer-lag port-channel 10
– no shutdown
– exit

– interface vlan 10
– untagged port-channel 10
– ip address 10.0.0.3/24
– no shutdown
– exit

– router ospf 1
– network 10.0.0.0/24 area 0
– network 30.0.0.0/24 area 0
– end
– write

Dell_S4810_3 Config:

– enable
– conf
– protocol spanning-tree rstp
– no disable
– bridge-priority 8192
– exit

– interface range tengigabitethernet 0/15 – 16
– no shutdown
– port-channel-protocol lacp
– port-channel 10 mode active
– exit

– int port-channel 10
– ip address 10.0.0.1/24
– no shutdown
– exit

– router ospf 1
– network 10.0.0.0/24 area 0
– end
– write

Note, the new “peer-routing timeout” command on both VLT peer switches. This is the command that enables VLT routing. The ‘timeout’ value is optional and is set to ‘0’ or no timeout by default. The value is entered in seconds and the maximum value it can be is ‘65535’. When the timer expires, the VLT peer is checked to see if it is available; if the VLT peer is not available, peer-routing is disabled on that peer. Below I show the output of the ‘show vlt brief’ command on both VLT peer switches to confirm VLT is up and running.

Dell_S4810_1 - 'show vlt brief' output

Dell_S4810_1 - 'show vlt brief' output


Dell_S4810_2 - 'show vlt brief' output

Dell_S4810_2 - 'show vlt brief' output

You can also see that I created loopback addresses for networks 40.0.0.0/24 and 50.0.0.0/24 on ‘Dell_S4810_4’. I did this so I had more networks to populate the OSPF database with. Below I confirm the routes in the routing table on ‘Dell_S4810_4’. Further below I then confirm that the routes are learned from OSPF and reachable on ‘Dell_S4810_3’ which has the lag connecting up to ‘Dell_S4810_1’ and ‘Dell_S4810_2’ via VLT. Welcome to VLT Routing!

Dell_S4810_4 - 'show ip route' displays routing table

Dell_S4810_4 - 'show ip route' displays routing table

Dell_S4810_3 - OSPF routes learned and reachable over VLT!

Dell_S4810_3 - OSPF routes learned and reachable over VLT!

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3 Responses to Dell Networking Extends Multipathing Capabilities with VLT Routing

  1. Tony Lizzerri says:

    Humair, thank you for the cofiguration demo, but you have not explained WHY anyone would want to do this? What problem does it solve? Where is the value? When would someone want to do this?

    vLT offers L2 multipathing, got that much.
    OSPF offers L3 multipathing.

    So, if I am going to deploy a routing protocol, like OSPF, that supports ECMP, why do I need vLT? What did this buy me?

  2. Adrian says:

    Hi Humair,

    I am trying to understand your scenario as I am in the process of configuring ospf between 2 VLTs.
    Does peer-routing actually help on configuring ospf or it just replaces the need to do VRRP to achieve redundancy on the host side and has nothing to do with ospf?
    Also, by looking at your routing table i see that you have two entries for each subnet, in other words 30.0.0.0/24 has two gateways 10.0.0.2 and 10.0.0.3, is that all right?
    I see exactly the same thing in my routing table, same subnet being advertised by both remote vlt members and not sure if that’s ok.
    I would appreciate your input.

  3. Brent says:

    Hi Humair / all

    if I had a peer routing in VLT DOmain both switches do I need to have a ip routing for intervlan routing? on both switches(S4810)

    also if I create a ACL also I need to configured both switches with the same ACL policy?

    Thank you very much
    BRent

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