[c-nsp] simple link aggregation

[Peter Rathlev]

On Mon, 2012-07-30 at 21:24 -0700, Mike wrote:
> I've googled and fiddled around and am unable to figure out simple
> link aggregation. I have a 3650 on one side, a 2970 on the other, and

3650? Or do you actually mean 3560, a switch? I'm assuming the latter.

> two 100mbps links that I want to set up aggregation with to provide a 
> (virtual) 200mbps pipe between them. Yes I understand the load sharing
> options and in this case I want to try round-robin.

Cisco's hardware forwarding platforms only support deterministic hashed
load sharing. What link member a specific packet uses is determined from
L2, L3 or L4 information or a combination of these. The 3560 and 2970
platforms support using L2 and/or L3 information:

Switch(config)#port-channel load-balance ?
  dst-ip       Dst IP Addr
  dst-mac      Dst Mac Addr
  src-dst-ip   Src XOR Dst IP Addr
  src-dst-mac  Src XOR Dst Mac Addr
  src-ip       Src IP Addr
  src-mac      Src Mac Addr

Switch(config)#

This deterministic load sharing is much better than (per packet) round
robin, since it lets you avoid out-of-order packets. All packets to/from
the same source/destination uses the same link members and are thus
subjected to that same latencies et cetera.

> I don't seem to see an easy/gentle how to do this and was hoping
> someone could tell me?

This document describes etherchannels on Catalyst switches and is worth
a read:

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

Configuring them is rather simple. Here's an example of an active LACP
port-channel trunk:

! *** Switch ***
default interface range FastEthernet0/1 - 2
interface range FastEthernet0/1 - 2
 switchport
 channel-group 1 mode active
!
interface Portchannel1
 switchport trunk encapsulation dot1q
 switchport mode trunk
 switchport trunk allowed vlan 10-20
 exit
!

Configuration for both CatOS and IOS can be found here:

http://www.cisco.com/en/US/tech/tk389/tk213/technologies_configuration_example09186a0080094470.shtml

-- 
Peter