Solved: ether channel load balancing

sarahr202 · ‎11-21-2008

hi every body!

let say two switches sw1 and sw2 have two hosts h1 and host h2 respectively. sw1 is connected to sw2 by trunks, we establish etherchannel on the trunks.

If isl is used for trunking, and ether channel is using src-dst-mac as load balancing method, will ether channel use source and destination mac in isl header to determine the link in etherchannel or it will use the source and destination mac belonging to hosts ?

How about in case of dotiq trunk which inserts only 4 byte tag in ethernet frame, would ether channel use the source and destination mac belonging to hosts for load balancing?

thanks a lot!

Mark Yeates · ‎11-21-2008

Sarah,

I beleive that the load balancing in host based to maintain the load balancing.

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.

HTH,

Mark

View solution in original post

padramas · ‎11-21-2008

Hello Sarah,

Both ISL/ Dot1Q VLAN Tag does not carry mac address information it.

http://www.firewall.cx/vlans-tagging.php

Ethernet header does have the mac address field and the following details the etherchannel load balancing operation.

http://www.cisco.com/en/US/tech/tk389/tk213/technologies_tech_note09186a0080094714.shtml

HTH

Padmanabhan

sarahr202 · ‎11-21-2008

thanks for your reply!

here is isl header

SA/DA/TYPE/USER/NLAN ID/ETHERNET FRAME/FCS

where SA source mac address of the switch which appends the isl header.

DA destination address which is a multicast address.

In my opinion,etherchannel looks at source and destination mac addresses of hosts, then determine the link in etherchannel, once the link is determined( which is in our case is trunk), then proper header (if isl is used) or tag( if dotiq is used) is inserted in the frame and then frame get transmitted on the link.

every body is welcome to correct me.

thanks a lot!

Mark Yeates · ‎11-21-2008

Sarah,

I beleive that the load balancing in host based to maintain the load balancing.

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.

HTH,

Mark