Posted on October 3, 2017 3:41 pm
 |  Asked by Pawel Gawel
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I need a help with proper design.

I have a pair 7050X with MLAG configuration. To the downstream devices I have 2 mlag port-channels each contain 2 links.

7050X will provide L3 functionality : gateways and routing.

 I would like to enabling ecmp and load-balance the traffic. What will be the best method to choose in this scenario ?


Thank you

Posted by Aesha Parikh
Answered on October 4, 2017 11:58 pm

Hi Pawel,

If I understood correctly, you want 7050X mlag pair to act as GW for downstream devices and would want to load balance traffic to both mlag peers. You can configure VARP (ip virtual-router address) and use an anycast Virtual IP as GW. Based on port-channel hashing, traffic will either hit mlag peer1 or peer 2. Both peers are in active-active router redundancy state meaning both peer can route traffic to spine. 

You can find more information on below link.

Posted by Pawel Gawel
Answered on October 6, 2017 1:41 pm

Hello Aesha,

Thank you for your information.Yes you understand me correctly.

I have a plan to use VARP, my question is more about the hashing algorithm, in my design which one should be good for me ?

Please see below.

Arista7050QX-32(config)#port-channel load-balance trident fields ip ?
destination-ip Use layer 3 IP destination address in the port channel hash for IP packets
destination-port Use layer 4 TCP/UDP destination port in the port channel hash for IP packets
ip-tcp-udp-header Use the layer 3/4 hashes in the port channel hash for IP packets
mac-header Use the MAC hash in the port channel hash for IP packets
source-ip Use layer 3 IP source address in the port channel hash for IP packets
source-port Use layer 4 TCP/UDP source port in the port channel hash for IP packets
symmetric-hash Use normalized addresses and ports in hash for IP packets


Thank you.

Posted by prajwala an
Answered on October 26, 2017 9:01 am

Hi Pawel,

From your initial mail, I understand that you have the topology as attached below :

Could you please clarify some of our questions , from where do you plan to load-balance the traffic ( upstream ( MLAG ) or downstream ) ?

If your requirement is to load balance traffic from MLAG to the downstream devices, it is something that is not possible. ( Assuming only one link is connected from a single MLAG peer to the downstream ) It is because each of these MLAG devices will forward traffic to either of the downstream devices depending on the destination of the packets. So here the traffic that egresses the MLAG peers in independent of hashing and is dependent only the destination.

Also could you clarify on the number of links from each of the MLAG switch to the downstream device .



Posted by prajwala an
Answered on October 27, 2017 3:50 am

Hi Pawel,

I have attached the topology diagram again.


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