Configuring the use of MAC addresses, or only the source IP addresses, might cause the distribution to be more balanced across all the bundled links. TIP To verify how effectively a configured load-balancing method is performing, you can use the show etherchannel port-channel command. Each link in the channel is displayed, along with a hex "Load" value.
Although this information is not intuitive, you can use the hex values to get an idea of each link's traffic loads relative to the others. In some applications, EtherChannel traffic might consist of protocols other than IP.
Recall that a router always uses its burned-in MAC address in Ethernet frames, even though it is forwarding packets to and from many different IP addresses.
In other words, many end stations send frames to their local router address with the router's MAC address as the destination. This means that the destination MAC address is the same for all frames destined through the router. Usually, this will not present a problem because the source MAC addresses are all different. When two routers are forwarding frames to each other, however, both source and destination MAC addresses remains constant, and only one link of the EtherChannel is used.
Beyond that, if most of the traffic is between the same two IP addresses, as in the case of two servers talking, choose IP port numbers to disperse the frames across different links.
A lot of digging, hope I understood documentation correctly and you will find my explanations useful. Please find links I have found interesting:. Why would mode on cause loops? How does spanning tree interoperate with one end etherchannel? I have started to write a reply, however realized there would be so much that it deserves separate article. In essence however just to not keep you waiting with mode on you are turning port-channel unconditionally, which means there is no check and as long as L1 is up port-channel will be up.
Etherchannel was created as a trick for spanning tree, so spanning tree sees port-channel as 1 link — BPDUs, the spanning tree packets, are running only through 1 link. This post was constructive indeed. May provide me same on cisco routers because the command are not support.
Hi Michal, Great article. Thank you. Switch sh int port-channel 1 Port-channel 1 is up, line protocol is up connected Hardware is EtherChannel, address is There is no command specify after sh int port-channel 1 Switch sh int port-channel 1? Packet Tracer is emulator with limited functionality, so it is expected that hardware specific commands would not work on packet tracer.
Those commands would work on Catalyst switches only. What box do you have? Anyway the answer is: it depends on hash bucket and on flows which you are trying, as balancing is hashed per flow.
It means that if you would have one flow on src dst pair you would limit traffic only to 1 gig as all flows would be hashed to one link only. More flows you would have, better distribution you would achieve. This is why best results you would achieve with 2, 4 or 8 links in the bundle. EtherChannel Load - Balancing Configuration :. Now we know everything right? Port - channel5 Primary aggregator. Ports in the Port-channel:. Ports in the Port - channel :. Comments Thank you verymuch, this article very useful.
Hello Joelson, Many thanks for the opinion! All interfaces in each EtherChannel must be the same speed, and you must configure all the interfaces as either Layer 2 or Layer 3 interfaces. EtherChannel reduces part of the binary pattern that is formed from the addresses in the frame to a numerical value that selects one of the links in the channel in order to balance the traffic load across the links in a channel. EtherChannel load balancing can use MAC addresses, IP addresses, or Layer 4 port numbers and either source mode, destination mode, or both.
Use of source or IP addresses can result in a better load balance. Load Balance must be configured globally and the load balancing option cannot be changed on a per port basis. Note: The switch uses the lower order bits of source MAC address and destination MAC address in order to determine which links must be used to transmit the data.
So if the data is received from the same source, then same link of the EtherChannel is used in order to forward the data. The software dynamically reallocates this address to another link in the channel if the link on which the address was learned is busier than the others. The switch chooses the link on the basis of the destination or source MAC address of the frame.
The default is to use the source MAC address. This default means that all packets that the switch receives on a non-Fast EtherChannel port with the same MAC source address that have a destination of the MAC addresses on the other side of the channel take the same link in the channel. The use of source-based forwarding in this situation evenly distributes traffic across all links in the channel. EtherChannel balances the traffic load across the links in a channel through the reduction of part of the binary pattern that the addresses in the frame form 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 mode applies to all EtherChannels that are configured on the switch. You can find out which interface is used in the EtherChannel to forward traffic based on the load balancing method.
The number of EtherChannels has the limit of six with eight ports per EtherChannel. The Catalyst series switches support both Layer 2 and Layer 3 EtherChannel, with up to eight compatibly configured Ethernet interfaces. The limit of the number of EtherChannels is the number of ports of the same type. With source-MAC address forwarding, when packets are forwarded to an EtherChannel, the packets 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, the packets are distributed across the ports in the channel based on the destination host 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.
For the series switch, when source-MAC address forwarding is used, load distribution based on the source and destination IP address is also enabled for routed IP traffic. All routed IP traffic chooses a port based on the source and destination IP address. Packets between two IP hosts always use the same port in the channel, and traffic between any other pair of hosts can use a different port in the channel.
The default port can be identified from the output of the command show etherchannel summary by a notation of d. With the enablement of PAgP, the two possible methods of link determination are preserve order and maximize load balancing between the links on the Fast EtherChannel.
The default is to maximize load balancing. PAgP is used to negotiate the configured method with the device at the other side of the channel. This provides the maximum possible load-balancing configuration. When Fast EtherChannel is configured with PAgP disabled, the switch cannot negotiate with the partner about the switch learning capability.
Whether the switch preserves frame ordering depends on whether the Fast EtherChannel partner performs source-based distribution. The active port is used for flooded traffic such as unknown unicast, unregistered multicast, and broadcast packets.
If the port-channel mode is on PAgP disabled , the active port is the link with the highest priority value. If the mode is desirable or auto PAgP enabled , the active port is selected based on the priority of the links on the switch that has the higher Ethernet address.
When two ports on the switch with the higher Ethernet address have the same priority, the port with the lower ifIndex is selected. When one link fails, all traffic that previously used that link now uses the link next to it. For example, if Link 1 fails in a bundle, traffic that previously used Link 1 before the failure now uses Link 2. PAgP aids in the automatic creation of EtherChannel links.
PAgP packets are sent between EtherChannel-capable ports in order to negotiate the formation of a channel. Some restrictions are deliberately introduced into PAgP. The restrictions are:. PAgP does not group ports that operate at different speeds or port duplex. If speed and duplex change when a bundle exists, PAgP changes the port speed and duplex for all ports in the bundle. PAgP modes are off, auto, desirable, and on.
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