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First of all, let's define the concepts of VPC, VSS and MLAG.
<blockquote>
vPC (Virtual Port-Channel), also known as multichassis EtherChannel
(MEC) is a feature on the Cisco Nexus switches that provides the
ability to configure a PortChannel across multiple switches (i.e vPC
peers). vPC is similar to Virtual Switch System (VSS) on the Catalysts
6500s.
MLAG is similar to VPC or VSS where LAG or link aggregation is a way
of bonding multiple physical links into a combined logical link. MLAG
or multi-chassis link aggregation extends this capability allowing a
downstream switch or host to connect to two switches configured as an
MLAG domain. This provides redundancy by giving the downstream switch
or host two uplink paths as well as full bandwidth utilization since
the MLAG domain appears to be a single switch to Spanning Tree (STP).
Because the MLAG domain appears to STP as a single switch there are no
blocked ports.
</blockquote>
<a href="https://i.stack.imgur.com/0t23l.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/0t23l.png" alt="enter image description here" /></a>
Now that we understand the basics of MLAG, let's dive into the configuration of MLAG.
First, let's verify and make sure the default control plane policy allows MLAG traffic to be handled by the CPU. Line 70 and 80 confirms that we have the correct ACE in place.
<pre><code>mlag-1#show ip access-lists 
 IP Access List default-control-plane-acl [readonly] 
 statistics per-entry 
 10 permit icmp any any [match 38, 3 days, 8:36:07 ago] 
 20 permit ip any any tracked [match 450111, 0:00:00 ago] 
 30 permit udp any any eq bfd ttl eq 255 
 40 permit ospf any any 
 50 permit tcp any any eq ssh telnet www snmp bgp https msdp [match 9, 0:19:12 ago] 
 60 permit udp any any eq bootps bootpc snmp rip ntp [match 4, 3 days, 12:10:07 ago] 
 70 permit tcp any any eq mlag ttl eq 255 [match 75, 3 days, 9:42:37 ago] 
 80 permit udp any any eq mlag ttl eq 255 
 90 permit vrrp any any 
 100 permit ahp any any 
 110 permit pim any any 
 120 permit igmp any any 
 130 permit tcp any any range 5900 5910 
 140 permit tcp any any range 50000 50100 
 150 permit udp any any range 51000 51100 
</code></pre>
Configure Port-Channel between the switches. Usually you would want to configure at least 2 links in the Port-Channels but 4 or 8 might be required if you have considerable amounts of data between the switches or for redundancy.
Port-channel between the switches
On both MLAG-1 and MLAG-2 switches
<pre><code>interface Ethernet 1 - 4 
 description port-channel 
 channel-group 10 mode active 
 
 interface port-channel 10 
 description port-channel 
 switchport mode trunk 
</code></pre>
Configure VLAN used by MLAG and disable spanning-tree on this VLAN.
On both MLAG-1 and MLAG-2 switches
<pre><code>vlan 4094 
 trunk group mlagpeer
 
 interface port-channel 10 
 switchport trunk group mlagpeer 

 no spanning-tree vlan 4094 
</code></pre>
We can safely disable spanning-tree because the trunk group ensures that VLAN 4094 will only traverse port-channel 10. Trunk group names must be identical on both switches for it to work properly.
Let's get the SVI configured on both switches so they can communicate.
<pre><code> MLAG-1# 
 interface vlan 4094 
 description MLAG_VLAN 
 ip address 172.20.1.1/30 
 no shut 

 MLAG-2# 
 interface vlan 4094 
 description MLAG_VLAN 
 ip address 172.20.1.2/30 
 no shut 
</code></pre>
Now the easy part on bringing up MLAG between the switches.
<pre><code>MLAG-1# 
 mlag 
 local-interface vlan 4094 
 peer-address 172.20.1.2 
 peer-link port-channel 10 
 primary-priority 1 
 domain-id mlagcore 

 MLAG-2# 
 mlag 
 local-interface vlan 4094 
 peer-address 172.20.1.1 
 peer-link port-channel 10 
 domain-id mlagcore
</code></pre>
Note:
Primary-priority is a hidden command and it is needed for the deterministic election of MLAG Primary switch and lower priority wins. Commands related to spanning-tree comes from the MLAG primary switch. For example, when you configure spanning-tree vlan root priority on the MLAG secondary switch, the setting will not take effect.
Once the communication establishes MLAG will be active.
Verification
Notice 'mlag-1' switch shows that it is MLAG primary and that the status of the MLAG is active on both switches.
The command show mlag is updated to show if the MLAG configuration is consistent or inconsistent compared with the peer configuration.
For example, here is the output if the configuration is consistent.
<pre><code>mlag-1#show mlag
MLAG Configuration:
domain-id : mlagcore
local-interface : Vlan4094
peer-address : 172.20.1.2
peer-link : Po10
peer-config : consistent 

MLAG Status: 
state : Active
negotiation status : Connected
peer-link status : Up
local-int status : Up
system-id : 02:1c:73:09:79:1b
 
MLAG Ports: 
Disabled : 0
Configured : 0
Inactive : 0
Active-partial : 0
Active-full : 4
</code></pre>
show mlag detail : Confirm MLAG is active, which peer is Primar­y/S­eco­ndary, timers, number of active­-fu­ll/­act­ive­-pa­rtial interf­aces, etc.
<a href="https://i.stack.imgur.com/SY3yE.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/SY3yE.png" alt="enter image description here" /></a>
show mlag config­-sanity : Run on both peers to confirm no incons­ist­encies or issues
show mlag interfaces [detai­l|m­emb­ers­|st­ates] : Confirm inform­ation on MLAG interf­aces.
show mlag issu warnings : Displays a warning message regarding the backwa­rd-­com­pat­ibility of this feature before upgrading.
tcpdump : #bash tcpdump -nei vlan4094 port 4432 ==&gt; to confirm control plane traffic for mlag is being sent and received.
It is also recommended that both MLAG-1 and MLAG-2 have identical LAYER 2 commands such as STP root priority etc. Because if the primary switch were to reboot, the secondary switch will takeover and STP commands would be different resulting in a sub-optimal configuration.
Now let's configure MLAG port-channel on MLAG-1 and MLAG-2 switch and also configure regular port-channel on the access layer switch AXS1. Highly recommended to use LACP ACTIVE and not just channel-group mode on.
<pre><code>mlag-1# 
 interface Ethernet11 
 description MLAG:PO_ASX1 
 no shutdown 
 channel-group 11 mode active 
 interface Port-Channel11 
 description MLAG:PO_ASX1 
 switchport mode trunk 
 mlag 11 


mlag-2# 
 interface Ethernet11 
 description MLAG:PO_ASX1 
 no shutdown 
 channel-group 11 mode active 
 interface Port-Channel11 
 description MLAG:PO_ASX1 
 switchport mode trunk 
 mlag 11


ASX1#
 interface Ethernet1/9 
 description MLAG:PO_TO_MLAG-1 
 switchport mode trunk 
 spanning-tree port type edge 
 channel-group 11 mode active 
 interface Ethernet1/11 
 description MLAG:PO_TO_MLAG-2 
 switchport mode trunk 
 channel-group 11 mode active 
</code></pre>
Let's verify that our port-channels are up on MLAG-1 and MLAG-2 to the ASX1 switch.
<pre><code> mlag-1#sh etherchannel detailed 
 Active Ports: 
 Port Time became active Protocol Mode 
 -------------------- ------------------------ ------ 
 Ethernet11 4:32:34 LACP Active 
 PeerEthernet11 4:34:24 LACP Active 


 mlag-1#show mlag interfaces detail 
 local/remote 
 mlag state local remote oper config last change changes 
 ------ ------------- ------- -------- ------- ---------- -------------- 
 1 active-full Po11 Po11 up/up ena/ena 0:08:23 ago 24 
</code></pre>
Notice that 'mlag-1#' shows 'PeerEthernet11' which is a good sign because it recognizes the other Ethernet11 on mlag-2 switch as a part of the port-channel.
<pre><code> ASX1# show port-channel summary 
 Flags: D - Down P - Up in port-channel (members) 
 I - Individual H - Hot-standby (LACP only) 
 s - Suspended r - Module-removed 
 S - Switched R - Routed 
 U - Up (port-channel) 
 M - Not in use. Min-links not met 
 -------------------------------------------------------------------------------- 
 Group Port- Type Protocol Member Ports 
 Channel 
 -------------------------------------------------------------------------------- 
 1 Po1(SU) Eth LACP Eth1/9(P) Eth1/11(P) 
</code></pre>
Notice that from ASX1 perspective this is just a normal port-channel with no special configurations. As far as ASX1 is concerned both Eth1/9 and Eth1/11 are connected into the same switch.
Spanning-tree show commands on both mlag-1 and mlag-2 switch.
<pre><code> mlag-1#sh spanning-tree vlan 101 
 Spanning tree instance for vlan 101 
 VL101 
 Spanning tree enabled protocol rapid-pvst 
 Root ID Priority 32869 
 Address 021c.7309.791b 
 This bridge is the root 
 Bridge ID Priority 32869 (priority 32768 sys-id-ext 101) 
 Address 021c.7309.791b 
 Hello Time 2.000 sec Max Age 20 sec Forward Delay 15 sec 
 Interface Role State Cost Prio.Nbr Type 
 ---------------- ---------- ---------- --------- -------- -------------------- 
 Po12 designated forwarding 1999 128.100 P2p 

 mlag-2#sh spanning-tree vlan 101 
 Spanning tree instance for vlan 101 
 VL101 
 Spanning tree enabled protocol rapid-pvst 
 Root ID Priority 32869 
 Address 021c.7309.791b 
 This bridge is the root 
 Bridge ID Priority 32869 (priority 32768 sys-id-ext 101) 
 Address 021c.7309.791b 
 Hello Time 2.000 sec Max Age 20 sec Forward Delay 15 sec 
 Interface Role State Cost Prio.Nbr Type 
 ---------------- ---------- ---------- --------- -------- -------------------- 
 Po11 designated forwarding 1999 128.100 P2p 
</code></pre>
Notice that both switches are acting as spanning-tree root bridge. Also note that the bridge address comes from the negotiated MLAG system-id (show mlag detail).
Caveats/Thoughts/Conclusions
<ul>
<li>Make sure to have a deterministic MLAG primary switch.</li>
<li>Set all STP commands the same on both switches.</li>
<li>At least have 2 links between the switches for MLAG communication in a port-channel for optimal redund­ancy.</li>
<li>If you have a single homed server, traffic might need to traverse the port-channel to the other switch adding an extra hop latency.</li>
<li>Turn off STP on the MLAG peering VLAN to prevent the peer link from going into the discarding state.</li>
<li>Recomm­ended to use VLAN4094 but any VLAN can be used. Use the same VLAN throughout all MLAG domains for consis­tency.</li>
<li>Put the MLAG peering VLAN into a trunk group to ensure this VLAN isn't used by any other ports and avoid any possible loop conditions being created.</li>
<li>Use &quot;no autost­ate­&quot; on the MLAG SVI to ensure this interface remains UP.</li>
<li>The Peer Link capacity should be equal to the Leaf-t­o-Spine total capacity to avoid losing capacity if the uplinks fail.</li>
<li>The MLAG Domain ID needs to be identical (case-­sen­sitive) across Peers as well as be unique in regards to other Leaf MLAG pairs.</li>
<li>The MLAG IDs need to match across Peers, but it is recomm­ended to use the same port-c­hannel ID across both Peers if possible for simplicity in operations and troubl­esh­ooting.</li>
<li>MLAG timers should be kept to the default values. Reload Delay is the interval that MLAG interfaces are disabled after an MLAG peer reboots. Non MLAG Reload Delay is the interval that non-MLAG links are disabled after an MLAG peer reboots.</li>
<li>After 4.21.1F, &quot;­swi­tchport mode trunk native vlan tag&quot; is no longer needed to be explicitly configured on the MLAG Peer Link.</li>
</ul>
<blockquote>
MLAG System ID : Derived after Primary Peer is elected (lowest MAC address); persistent across reboots; LACP and STP control packets uses this to emulate one &quot;­log­ica­l&quot; switch.
</blockquote>
<blockquote>
STP : Active only on the Primary Peer; config­uration needs to be consistent across both peers for seamless failover; Secondary will forward BPDUs to Primary across the Peer Link.
</blockquote>
<blockquote>
TCP and UDP Port 4432 : Must be permitted in control plane ACL on both peers if non-de­fault control plane ACL is used.
</blockquote>
<blockquote>
MAC address table : Sync'ed between MLAG peers for active­/active member ports.
</blockquote>
<blockquote>
IGMP Snooping Tables : Sync'ed between MLAG peers for active­/active member ports; config­uration should be consistent across both peers.
</blockquote>
<blockquote>
ARP table sync? : No ARP table sync with MLAG.
</blockquote>
<blockquote>
L3 Sync? : MLAG is L2 active­/active techno­logy. To get an active­/active L3 Gateway use VARP, but keep in mind that though MLAG forms one logical switch between two switches, there are two separate Layer 3 control planes on each peer.
</blockquote>
Ref: <a href="https://aristanetworks.force.com/AristaCommunity/s/article/mlag-basic-configuration" rel="nofollow noreferrer">https://aristanetworks.force.com/AristaCommunity/s/article/mlag-basic-configuration</a>
Ref: <a href="https://www.arista.com/en/support/toi/eos-4-15-2f/13733-mlag-config-check" rel="nofollow noreferrer">https://www.arista.com/en/support/toi/eos-4-15-2f/13733-mlag-config-check</a>
Ref: <a href="https://aristanetworks.force.com/AristaCommunity/s/question/0D52I00007ERqClSAL/replacing-vpc-of-network" rel="nofollow noreferrer">https://aristanetworks.force.com/AristaCommunity/s/question/0D52I00007ERqClSAL/replacing-vpc-of-network</a>
Ref: <a href="http://ithitman.blogspot.com/2014/08/configuring-arista-mlag-basic-setup.html" rel="nofollow noreferrer">http://ithitman.blogspot.com/2014/08/configuring-arista-mlag-basic-setup.html</a>
Ref: <a href="https://cheatography.com/sh-arista/cheat-sheets/arista-mlag/" rel="nofollow noreferrer">https://cheatography.com/sh-arista/cheat-sheets/arista-mlag/</a>

I have EVE-NG up and running and Have successfully imported an Arista EOS image. Connected a couple of VPCS to it. But I can't seem to get them to ping each other. I did assign IPs to the VPCS for testing but no luck. Wondering what needs to be done on switch side for the two computers to be able to see each other. I thank you in advance for any help you are able to provide.

Arista vEOS and EVE-NG setup

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我已经启动并运行了EVE-NG，并成功导入了Arista EOS映像.连接了几个VPCS。但我似乎不能让他们互相调情。我确实为VPCS分配了I进行测试，但没有运气。想知道这两台电脑需要在开关边做些什么才能看到对方。我预先感谢您所能提供的任何帮助。

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