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When "mclag-separate-ip" Should be Used in Dell Networking Enterprise SONiC OS MF-CLI

Summary: This article explains when the feature "mclag-separate-ip" should be used in VLAN interfaces.

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Instructions

Dell Enterprise SONiC "mclag-separate-ip" Usage

By default, a given VLAN on both MC-LAG peers uses the same MAC and IP addresses, which prevents L3 protocols to pass traffic between them.

To enable L3 protocols such as BGP, OSPF, and BFD, to transmit packets on VLANs between MC-LAG peers, configure each peer VLAN interface using "mclag-separate-ip" command.
 
NOTE: If a gateway MAC is configured with "mclag-separate-ip" on the VLAN interfaces, the VLANs take different MAC addresses. See the following Dell article 191547. How to Configure a Gateway MAC Address in Dell Networking SONiC MF-CLI for more details.
 

Command Syntax

Command Explanation
admin@sonic:~$ sonic-cli Enter DELL SONiC MF-CLI.
sonic# configure terminal Enter configuration mode.
sonic(config)# interface vlan <ID> Enter VLAN interface.
sonic(conf-if-VlanX)# no Ip address <Ip address or subnet> Remove any exiting IP address from interface.
sonic(conf-if-VlanX)# mclag-separate-ip Configure "mclag-separate-ip."
sonic(conf-if-VlanX)# Ip address <Ip address or subnet> Assign the IP address.

Verification
Command Explanation
sonic# show mclag separate-ip-interfaces Show separate-ip-interfaces in MC-LAG.

Sample output
 
Sample output from show mclag separate-ip-interfaces command
Figure 1: Sample output from show mclag separate-ip-interfaces command.
 

Explanation

Here, we explain with the topology diagram seen below.
Sample MC-LAG Topology
Figure 2: Sample MC-LAG Topology

IP Address 
Active VLAN 25 IP address     : 10.0.0.1 /24
Standby VLAN 25 IP address    : 10.0.0.2 /24
Downstream VLAN 25 IP address : 10.0.0.3 /24
Consider we are pinging from downstream to Active and Standby member VLAN 25 IP address.
 
Pinging Active and Standby VLAN members shows unreachable
Figure 3: Pinging Active and Standby VLAN members shows unreachable.

We do not have reachability to 10.0.0.2.

When inspecting the ARP Entry for the IP address in the Downstream switch, we see both 10.0.0.1 and 10.0.0.2 have the same MAC address.
 
ARP IP addresses show the same MAC Address
Figure 4: ARP IP addresses show the same MAC Address. 
 
Now let us configure "mclag-separate-ip" in interface VLAN 25 on both peers.
 
NOTE: We have to remove any existing IP address, configure "mclag-separate-ip," and assign IP back.
 
Screenshot of configure interface VLAN 25 in MCLAGSW1
Figure 5: Screenshot of configure interface VLAN 25 in MCLAGSW1.
 
Screenshot of configure interface VLAN 25 in MCLAGSW2
Figure 6: Screenshot of configure interface VLAN 25 in MCLAGSW2.

We can ping to both Active and Standby Peer.
 
Pinging Active and Standby VLAN members shows reachable
Figure 7: Pinging Active and Standby VLAN members shows reachable.

ARP Entry for the IP address in downstream switch
 
ARP IP addresses show different MAC Address
Figure 8: ARP IP addresses show different MAC Address.

Affected Products

PowerSwitch S6000 ON, PowerSwitch S5248F-ON, PowerSwitch S5296F-ON, PowerSwitch S6100-ON, PowerSwitch Z9100-ON, PowerSwitch Z9264F-ON, PowerSwitch Z9332F-ON
Article Properties
Article Number: 000191392
Article Type: How To
Last Modified: 30 Jun 2023
Version:  3
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