Symptoms

MC-LAG is affected when the keepalive session status goes down in SONiC.The following MC-LAG status is seen at the time of the keepalive session down: SONIC-1# show mclag brief Domain ID : 1 Role : active Session Status : down Peer Link Status : up Source Address : 192.168.2.1 Peer Address : 192.168.2.2 Peer Link : PortChannel100 Keepalive Interval : 1 secs Session Timeout : 30 secs Delay Restore : 300 secs System Mac : XX:XX:XX:XX:XX:XX Mclag System Mac : 00:00:00:00:00:01 Number of MLAG Interfaces:1 ----------------------------------------------------------- MLAG Interface Local/Remote Status ----------------------------------------------------------- PortChannel1 up/unknown

Cause

MC-LAG gets affected when the keepalive session status goes down in SONiC. The keepalive in SONiC is configured with IPv4 L3 communication similar to the backup-link in OS9 and OS10, which usually is not affecting VLT-Portchannel status. The peer-link status in OS9 and OS10 is going to affect VLT-Portchannel status instead. However, in SONiC, the keepalive session status has to be up in order to MC-LAG to be up. For the keepalive link, carries periodic heartbeat between MC-LAG peer devices and is also used to synchronize the state between MC-LAG peer devices. As opposed to SONiC, OS9 and OS10 use the peer-link to synchronize state between VLT peer devices.Once the keepalive session link gets down, MC-LAG status on both of the MC-LAG peer devices becomes up/unknown because of the synchronization failure between both peer devices.In Normal State SONIC-1#show version Software Version : 4.1.0-Enterprise_Base Product : Enterprise SONiC Distribution by Dell Technologies Distribution : Debian 10.13 Kernel : 5.10.0-8-2-amd64 Config DB Version : version_4_1_1 Build Commit : 93589a15db Build Date : Tue Apr 18 17:56:48 UTC 2023 Built By : sonicbld@sonic-lvn-csg-001 Platform : x86_64-kvm_x86_64-r0 HwSKU : DellEMC-S5248f-P-25G-DPB SONIC-1# show ip interfaces Flags: U-Unnumbered interface, A-Anycast IP ----------------------------------------------------------------------------------------------------------------- Interface IP address/mask VRF Admin/Oper Flags ----------------------------------------------------------------------------------------------------------------- PortChannel200 192.168.2.1/24 up/up Vlan636 172.16.0.1/24 up/up SONIC-1# SONIC-1# SONIC-1# show PortChannel summary Flags(oper-status): D - Down U - Up (portchannel) P - Up in portchannel (members) ---------------------------------------------------------------------------------------------------------------------------- Group PortChannel Type Protocol Member Ports ---------------------------------------------------------------------------------------------------------------------------- 1 PortChannel1 (U) Eth LACP Eth1/1(P) 100 PortChannel100 (U) Eth NONE Eth1/8(P) Eth1/9(P) 200 PortChannel200 (U) Eth LACP Eth1/5(P) Eth1/6(P) SONIC-1# SONIC-1# SONIC-1# show mclag brief Domain ID : 1 Role : active Session Status : up Peer Link Status : up Source Address : 192.168.2.1 Peer Address : 192.168.2.2 Peer Link : PortChannel100 Keepalive Interval : 1 secs Session Timeout : 30 secs Delay Restore : 300 secs System Mac : XX:XX:XX:XX:XX:XX Mclag System Mac : 00:00:00:00:00:01 Number of MLAG Interfaces:1 ----------------------------------------------------------- MLAG Interface Local/Remote Status ----------------------------------------------------------- PortChannel1 up/up SONIC-1# SONIC-1# SONIC-1# show running-configuration interface PortChannel 1 ! interface PortChannel1 mode active switchport trunk allowed Vlan 636 no shutdown mclag 1 SONIC-1# show running-configuration interface PortChannel 100 ! interface PortChannel100 mode on switchport trunk allowed Vlan 1-4094 no shutdown SONIC-1# show running-configuration interface PortChannel 200 ! interface PortChannel200 mode active no shutdown ip address 192.168.2.1/24 SONIC-1# SONIC-1# SONIC-1# ping 172.16.0.3 //IP address assigned to VLAN636 on uplink SW. PING 172.16.0.3 (172.16.0.3) 56(84) bytes of data. 64 bytes from 172.16.0.3: icmp_seq=1 ttl=64 time=3.26 ms 64 bytes from 172.16.0.3: icmp_seq=2 ttl=64 time=3.47 ms 64 bytes from 172.16.0.3: icmp_seq=3 ttl=64 time=3.21 ms 64 bytes from 172.16.0.3: icmp_seq=4 ttl=64 time=2.84 ms 64 bytes from 172.16.0.3: icmp_seq=5 ttl=64 time=11.1 ms ^C SONIC-1# SONIC-2#show version Software Version : 4.1.0-Enterprise_Base Product : Enterprise SONiC Distribution by Dell Technologies Distribution : Debian 10.13 Kernel : 5.10.0-8-2-amd64 Config DB Version : version_4_1_1 Build Commit : 93589a15db Build Date : Tue Apr 18 17:56:48 UTC 2023 Built By : sonicbld@sonic-lvn-csg-001 Platform : x86_64-kvm_x86_64-r0 HwSKU : DellEMC-S5248f-P-25G-DPB SONIC-2# show ip interfaces Flags: U-Unnumbered interface, A-Anycast IP ----------------------------------------------------------------------------------------------------------------- Interface IP address/mask VRF Admin/Oper Flags ----------------------------------------------------------------------------------------------------------------- PortChannel200 192.168.2.2/24 up/up Vlan636 172.16.0.2/24 up/up SONIC-2# SONIC-2# SONIC-2# show PortChannel summary Flags(oper-status): D - Down U - Up (portchannel) P - Up in portchannel (members) ---------------------------------------------------------------------------------------------------------------------------- Group PortChannel Type Protocol Member Ports ---------------------------------------------------------------------------------------------------------------------------- 1 PortChannel1 (U) Eth LACP Eth1/1(P) 100 PortChannel100 (U) Eth NONE Eth1/8(P) Eth1/9(P) 200 PortChannel200 (U) Eth LACP Eth1/5(P) Eth1/6(P) SONIC-2# SONIC-2# SONIC-2# show mclag brief Domain ID : 1 Role : standby Session Status : up Peer Link Status : up Source Address : 192.168.2.2 Peer Address : 192.168.2.1 Peer Link : PortChannel100 Keepalive Interval : 1 secs Session Timeout : 30 secs Delay Restore : 300 secs System Mac : XX:XX:XX:XX:XX:XX Mclag System Mac : 00:00:00:00:00:01 Number of MLAG Interfaces:1 ----------------------------------------------------------- MLAG Interface Local/Remote Status ----------------------------------------------------------- PortChannel1 up/up SONIC-2# SONIC-2# SONIC-2# SONIC-2# SONIC-2# show running-configuration interface PortChannel 1 ! interface PortChannel1 mode active switchport trunk allowed Vlan 636 no shutdown mclag 1 SONIC-2# show running-configuration interface PortChannel 100 ! interface PortChannel100 mode on switchport trunk allowed Vlan 1-4094 no shutdown SONIC-2# show running-configuration interface PortChannel 200 ! interface PortChannel200 mode active no shutdown ip address 192.168.2.2/24 SONIC-2# SONIC-2# SONIC-2# ping 172.16.0.3 PING 172.16.0.3 (172.16.0.3) 56(84) bytes of data. 64 bytes from 172.16.0.3: icmp_seq=1 ttl=64 time=3.48 ms 64 bytes from 172.16.0.3: icmp_seq=2 ttl=64 time=2.94 ms ^CSONIC-2# In Problem State (Keepalive-link Status Down by Shutting Down Po200 Member Ports) SONIC-1# show mclag brief Domain ID : 1 Role : active Session Status : down Peer Link Status : up Source Address : 192.168.2.1 Peer Address : 192.168.2.2 Peer Link : PortChannel100 Keepalive Interval : 1 secs Session Timeout : 30 secs Delay Restore : 300 secs System Mac : XX:XX:XX:XX:XX:XX Mclag System Mac : 00:00:00:00:00:01 Number of MLAG Interfaces:1 ----------------------------------------------------------- MLAG Interface Local/Remote Status ----------------------------------------------------------- PortChannel1 up/unknown SONIC-1# SONIC-1# SONIC-1# ping 172.16.0.3 PING 172.16.0.3 (172.16.0.3) 56(84) bytes of data. 64 bytes from 172.16.0.3: icmp_seq=1 ttl=64 time=8.00 ms 64 bytes from 172.16.0.3: icmp_seq=2 ttl=64 time=3.08 ms 64 bytes from 172.16.0.3: icmp_seq=3 ttl=64 time=2.99 ms 64 bytes from 172.16.0.3: icmp_seq=4 ttl=64 time=2.92 ms 64 bytes from 172.16.0.3: icmp_seq=5 ttl=64 time=3.07 ms ^C SONIC-1# SONIC-2# show PortChannel summary Flags(oper-status): D - Down U - Up (portchannel) P - Up in portchannel (members) ---------------------------------------------------------------------------------------------------------------------------- Group PortChannel Type Protocol Member Ports ---------------------------------------------------------------------------------------------------------------------------- 1 PortChannel1 (U) Eth LACP Eth1/1(P) 100 PortChannel100 (U) Eth NONE Eth1/8(P) Eth1/9(P) 200 PortChannel200 (D) Eth LACP Eth1/5(D) Eth1/6(D) SONIC-2# show mclag brief Domain ID : 1 Role : standby Session Status : down Peer Link Status : up Source Address : 192.168.2.2 Peer Address : 192.168.2.1 Peer Link : PortChannel100 Keepalive Interval : 1 secs Session Timeout : 30 secs Delay Restore : 300 secs System Mac : XX:XX:XX:XX:XX:XX Mclag System Mac : 00:00:00:00:00:01 Number of MLAG Interfaces:1 ----------------------------------------------------------- MLAG Interface Local/Remote Status ----------------------------------------------------------- PortChannel1 up/unknown SONIC-2# SONIC-2# ping 172.16.0.3 PING 172.16.0.3 (172.16.0.3) 56(84) bytes of data. From 172.16.0.2 icmp_seq=1 Destination Host Unreachable From 172.16.0.2 icmp_seq=1 Destination Host Unreachable From 172.16.0.2 icmp_seq=1 Destination Host Unreachable From 172.16.0.2 icmp_seq=1 Destination Host Unreachable ^C

Resolution

In order for MC-LAG to keep up and running without any issue, the keepalive link status also must keep up and running. Management port is normally used for the keepalive link, but port channel with IP address assigned to it can be used for the keepalive link for redundancy purposes. The behavior (that MC-LAG will be affected when the keepalive link status gets down) described in this KB article is expected in all the versions at least until SONiC version 4.2.0.

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