Jaycee's Networking

May 10, 2009

EtherChannel

Filed under: Information, IOS — Tags: , — Jaycee @ 8:17 pm

A. EtherChannel :

1. A Cisco term for the technology that enables the bonding of up to 8 physical Ethernet links into a single logical link. However, the bandwidth is not truly the aggregate of the physical link speeds in all situations. (an EtherChannel composed of 4 1-Gbps links, each conversation will still be limited to 1 Gbps by default.

2. By default, the physical link used for each packet is determined by the packet’s destination MAC address. This algorithm is Cicso-proprietary. The packets with the same destination MAC address will always travel over the same physical link. => It ensures that packets sent to a single destination MAC address never arrive out of order.

3. If one workstation talks to one server over an EtherChannel, only one of the physical links will be used. All of the traffic destinated for that server will traverse a single physical link in the EtherChannel. => A single user will only ever get 1 Gbps from the EtherChannel at a time.

4. Solaris uses “Trunk” for this technology term.

B. Load Balancing:

1. Hashing algorithm takes the destination MAC address and hashes that value to a number in the range of 0-7.

2. The only possible way to distribute traffic equally across all links in an EtherChannel is to design one with 8, 4, or 2 physical links.

3. The method the switch uses to determine which path to assign can be changed:

a. MAC address:

(1) source MAC
(2) destination MAC (default)
(3) source and destination MAC

b. IP address:

(1) source IP
(2) destination IP
(3) source and destination IP

c. Ports:

(1) source port
(2) destination port
(3) source and destination ports

4.In the case of one server (i.e. email server) receiving the lion’s share of the traffic, destination MAC address load balancing doesn’t make sense. Give this scenario, balancing with the source MAC address makes more sense as the example below:

EtherChannel load-balancing factors

a. Load-balancing method is only applied to packets being transmitted over the EtherChannel. This is not a 2-way function.

b. When packets are being returned from the email server, the source MAC address is that of the email server itself.

c. Thus, the soluction would be to have source MAC address load balancing on Switch A, and destination load balancing on Switch B.

5. For a switch like 6509, changing the load-balancing algorithm is done on a chassis-wide basis, so with all the devices connected to a single switch as below:

Single server to single NAS

Problem: the bandwidth required between the server and the NAS device is in excess of 2 Gbps.

a. Solution 1: change the server and/or NAS device so that each link has its own MAC adddress => the packets ill still be source from and destined for only one of those addresses.

b. Solution 2: Spliting the link into 4 x 1-Gbps links, each with its own IP network and mounting different filesystems on each link will solve the problem.

c. Solution 3: get a faster physical link, wush as 10Gbps Ethernet.

C. EtherChannel Protocols:

EtherChannel protocols and their modes

1. LACP (Link Aggregation Control Protocol) is IEEE standard.

2. PAgP (Port Aggregation Control Protocol) is Cisco-proprietary.

3. NetApp NAS devices dont negotiate with the other sides of the links, so Cisco side of the EtherChannel should set to “on“.

D. EtherChannel Configuration:

1. Creat a port-channel virtual interface:

EtherChannel configuration

2. Shows the status of an EtherChannel:

sh etherchannel sum

3. Shows the number of bits used in the hash algorithm for each physical interface:

sh etherchannel 1 port-channel

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