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We have a 4Gb (4x1G) LAG trunk with LACP between two cisco switches (c3850<--->c4948) and i am noticing that it is not doing proper load-balancing. I found SW1 using src-dst-ip algorithm and SW2 using src-mac algorithm. Are both of these algorithms supposed to be same?

What is the best load-balancing method that I should use?

We have mixed traffic in our environment including VoIP, TCP/UDP, SAN backup nightly etc.

SW1:

SW1#show etherchannel load-balance
EtherChannel Load-Balancing Configuration:
        src-dst-ip

EtherChannel Load-Balancing Addresses Used Per-Protocol:
Non-IP: Source XOR Destination MAC address
  IPv4: Source XOR Destination IP address
  IPv6: Source XOR Destination IP address 

SW2:

SW2>show etherchannel load-balance
EtherChannel Load-Balancing Configuration:
        src-mac

EtherChannel Load-Balancing Addresses Used Per-Protocol:
Non-IP: Source MAC address
  IPv4: Source MAC address
  IPv6: Source MAC address

EDIT:

Notes: We don't have a router, all we have is a L2 switched network. We have many servers behind trunk, so should i use src-dst-ip? or src-dst-mac ?

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We don't have router, all we have L2 switch network. We have many servers behind trunk, so should i use src-dsp-ip? or src-dst-mac ?

You need to weigh several factors to determine which method to use in different places on your network. Different network engineers will come up with different recommendations. This is really leading to opinion-based answers, and it is probably better suited for a discussion on Network Engineering Chat.

Cisco has some guidance that you should understand:

Chapter: Configuring EtherChannels

Load-Balancing and Forwarding Methods

EtherChannel balances the traffic load across the links in a channel by reducing part of the binary pattern formed from the addresses in the frame to a numerical value that selects one of the links in the channel. EtherChannel load-balancing can use MAC addresses or IP addresses, source or destination addresses, or both source and destination addresses. The selected mode applies to all EtherChannels configured on the switch. You configure the load-balancing and forwarding method by using the port-channel load-balance global configuration command.

With source-MAC address forwarding, when packets are forwarded to an EtherChannel, they are distributed across the ports in the channel based on the source-MAC address of the incoming packet. Therefore, to provide load-balancing, packets from different hosts use different ports in the channel, but packets from the same host use the same port in the channel.

With destination-MAC address forwarding, when packets are forwarded to an EtherChannel, they are distributed across the ports in the channel based on the destination host's MAC address of the incoming packet. Therefore, packets to the same destination are forwarded over the same port, and packets to a different destination are sent on a different port in the channel.

With source-and-destination MAC address forwarding, when packets are forwarded to an EtherChannel, they are distributed across the ports in the channel based on both the source and destination MAC addresses. This forwarding method, a combination source-MAC and destination-MAC address forwarding methods of load distribution, can be used if it is not clear whether source-MAC or destination-MAC address forwarding is better suited on a particular switch. With source-and-destination MAC-address forwarding, packets sent from host A to host B, host A to host C, and host C to host B could all use different ports in the channel.

With source-IP address-based forwarding, when packets are forwarded to an EtherChannel, they are distributed across the ports in the EtherChannel based on the source-IP address of the incoming packet. Therefore, to provide load-balancing, packets from different IP addresses use different ports in the channel, but packets from the same IP address use the same port in the channel.

With destination-IP address-based forwarding, when packets are forwarded to an EtherChannel, they are distributed across the ports in the EtherChannel based on the destination-IP address of the incoming packet. Therefore, to provide load-balancing, packets from the same IP source address sent to different IP destination addresses could be sent on different ports in the channel. But packets sent from different source IP addresses to the same destination IP address are always sent on the same port in the channel.

With source-and-destination IP address-based forwarding, when packets are forwarded to an EtherChannel, they are distributed across the ports in the EtherChannel based on both the source and destination IP addresses of the incoming packet. This forwarding method, a combination of source-IP and destination-IP address-based forwarding, can be used if it is not clear whether source-IP or destination-IP address-based forwarding is better suited on a particular switch. In this method, packets sent from the IP address A to IP address B, from IP address A to IP address C, and from IP address C to IP address B could all use different ports in the channel.

Different load-balancing methods have different advantages, and the choice of a particular load-balancing method should be based on the position of the switch in the network and the kind of traffic that needs to be load-distributed. In Figure 40-5, an EtherChannel of four workstations communicates with a router. Because the router is a single-MAC-address device, source-based forwarding on the switch EtherChannel ensures that the switch uses all available bandwidth to the router. The router is configured for destination-based forwarding because the large number of workstations ensures that the traffic is evenly distributed from the router EtherChannel.

Use the option that provides the greatest variety in your configuration. For example, if the traffic on a channel is going only to a single MAC address, using the destination-MAC address always chooses the same link in the channel. Using source addresses or IP addresses might result in better load-balancing.

Figure 40-5 Load Distribution and Forwarding Methods

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You need to remember that on a etherchannel, on bot switches you can balance the data you want to transmit (there is no problem if exist differences of the algorithm on bot ends)if you do that on bot ends, you will be getting a load balance on your link. By other hand, to choose the correct algorithm, you need to think on the form that data is transmited, if source is one ip, on mac-address, destination is one ip, one mac-address, to get the correct load balance method.

Eg, if the source you will be getting it is a great number of ip, i think you can tried with src-ip, if you will be getting a lot of differents mac, src-mac if what you need.

This is the trick for load balance, and the reason why we sometimes put a correct configuration, and we don't see nothing of load balance on our etherchannel links.

Remember, router changes mac address and put it owns like mac address source on outbound packets, that's it, if a lan is connected to a router, and then behind a router is are connected your switches and your etherchannel, i guess you will NOT get a great differences of mac address...

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  • I have updated my question with additional info: – Satish Jun 11 '16 at 16:41
  • With that, if all your network is "Layer 2", i guess you can tried with src-dst-mac – Orlando Gaetano Jun 11 '16 at 16:45
  • Doesn't L2 Layer support src-dst-ip ? – Satish Jun 11 '16 at 16:50
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    Yes, it is also supported on your scenario – Orlando Gaetano Jun 11 '16 at 16:56

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