# Simulating a EtherChannel interface with VLAN trunking

## gtsquirrel

Hey,

I have a Gentoo server connected to a Cisco Catalyst 2950 24-port switch via eth0 on port FastEthernet0/24.  I have Fa0/24 configured to be an 802.1q VLAN trunk line, and have added the appropriate VLANs to eth0.  Thus far, everything works great!

Now I want more network bandwidth to the server.  It's already at 100 Mbps full duplex, but who wants to settle for a measly 200 Mbps?  As such, I started playing around with Fast EtherChannel (FEC) on the 2950.  I found the Linux Channel Bonding project as a solution for getting this to work on the Gentoo server.

So now my questions ... has anyone out there played with this Linux EtherChannel in combination with VLANs?  What are the caveats I should know about?  Have you seen a big performance gain?  Etc.?

Any information would be great.  Thanks!

chris

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## ewtrowbr

IMHO, Etherchannel underperforms, especially when you are talking about connectivity to a host. Where it does make sense is when you have a large number of hosts that all want to talk to each other across a multiple switchs, like in a p2p environment, and you use etherchannel on the switch trunk.

EtherChannel distributes frames 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.  It performs a binary XOR of the final bits of the destination mac address of the forwarded frame. It chooses a link based on this operation. 

Since your gentoo box will (probably) maintain a single MAC address, packets traveling to the gentoo device will always use the same trunk. Datagrams will be distributed poorly. This is all because of the asychronous character of ethernet. 

Go ahead and play with the technology and report back to the group. I'd be interested to see how it works out. But if you're dealing in a production environment, consider gigabit or 10G ethernet.

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## ewtrowbr

This just occured to me... you can increase the performance of you 802.1q trunk with etherchannel, by making sure the 802.1q interfaces on the Gentoo server have different functional MAC addresses. I'm not sure how the linux kernel handles this... 

Sun used to have a quad fastE card that shipped with all ports using the same MAC address... drove me nuts.

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## gtsquirrel

I will definitely post my findings,  thanks for the information!

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