WHY NOT? Port-Channel over catalyst C3750 and Cisco 7206VXR (NPE-G2) not share equitably traffic for all Interface

[Wiyat Spain]

Dear

Community Support

I have running a Port-Channel over catalyst C3750 and Cisco 7206VXR (NPE-G2) join between then three cable:

7206:Gi0/1   ------------------- C3750: Gi1/0/3

         Gi0/2   -------------------              Gi1/0/4

         Gi0/3   -------------------              Gi1/0/5

My problem:

   The Major part of the traffic only that use one Interface and I expect that the total of the traffic will be share equitably between the       three interface, but now my situation is that I use 950MB over the Gi01 on Router 7206 and sometime I have a saturation between the C3750 and Router 7206.

I read it on Internet on the following link this: (I apologize for this, but LACP is not supported on the 7200 platform, only manual/static GEC (Gigabit EtherChannel) configuration is allowed here.)

https://supportforums.cisco.com/discussion/12395086/7200-7204-vxr-lacp-problem

I understand that with Router 7200 is impossible to make a LACP and share equitably the data between all interfaces that are member of the Port-channel.

My question are:

Do you know any option or alternative that I make possible to share equitable the traffic over all interfaces when the LACP not work over the Router 7200?

The option that you will be recommend, do you consider that will be generate an impact over the performance or High CPU.

Actually I am running OSPF over the Router 7200..

Please send me back your comments,

regards

[Jon Marshall]

LACP has nothing to do with how traffic is shared across the links, it is simply a protocol used to form etherchannels.

So that is not the issue.

With etherchannel a single flow between two end devices cannot be spread across links in the etherchannel.

A flow is simply a unique connection between two end devices.

How the flow is identified as unique depends on the load balancing methods available on each platform eg.  src/dst mac address, IP or ports etc. or a combination and not all platforms support all methods.

So if most of the flows are small but you had a couple of large flows and the large flows were sent on the same link in the etherchannel you would get an uneven distribution.

Put simply etherchannel takes no account of the actual load on each of the links, it simply selects a link based on the load balancing method it has been configured to use.

You can tell etherchannel which load balancing method to use and it can make a big difference ie.if all traffic is destined to a default gateway on the 7200 then the dst mac address of the packets would always be the same so using dst mac as the load balancing choice would not give you an even spread.

In that case using dst IP would be better.

You can use a different load balancing method at either end of the link although I don't know what the 7200 supports.

In the end though etherchannel is as much about redundancy as it is about extra bandwidth and you willl probably not be able to get a completely even traffic distribution across all the links.

Edit - one other point, using an even number of links in your etherchannel would also help distribute the load more evenly because of the way the load balancing algorithm works.

Jon

[Joseph W. Doherty · Accepted solution]

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Posting

To add to Jon's post, the 3750 does support different load balancing algorithms, and the default often should be changed.  Source/destination IP often works well.

Also like Jon, I don't know if the 7200 supports various load balancing algorithms.

As Jon also mentioned, load balancing generally works worst with an odd number of links.  It generaly works best with a power of two number of ports.

An alternative to Etherchannel, if your 3750 is L3, you might run your 3 links as p2p routed links.  This may load balance better on your 3 links.

One issue with Etherchannel or ECMP routed links, it's a static load balancing, i.e. one of the links might be congested and other traffic will still be directed to it.  If you use routed p2p links, the 7200 might be alble to support OER/PfR.  If it does, it can dynamically load balance.  Unfortunately, that feature won't be found with your 3750.

[Wiyat Spain]

Dear Joseph,

Thank you for reply.

On the meantime, that I buy it an equipment I need to give an solution to my existing network, without increase to High CPU.

When we start to work we have an BGP, OSPF, ACL process runing on the same router when the traffic going up the CPU on BGP and OSPF process we look that the cpu up and when the traffic down the CPU too.- We fix it this problem separate the process installed two router.- We coming working with out any problem.

The problem start again when we look that the traffic up more or less 900Mb to 1GB of usage on the Gi01 from the router point of view, I look high latency.

For this reason, i create a port-channel with two interface Gi01 and Gi02 and Graph both interface for 1 week and the result was that the Gi01 all the time have 900MB and the Gi02 only that have 300MB, without any experience and following forum I take the determination to add a new member into my port-channel the Gi03 expecting that the traffic will be load balance between the three Interfaces but wasnt.

For this reason I post this here to take the experience of the forum to understand what is the better way to create a Load balance using:

catalyst C3750 and Cisco 7206VXR (NPE-G2)

Obviously that, wherever option that you will be recomend; What we need to expect on the CPU performance.:

1. Will be increase or not?

2. Keep on 45% where I have now?

I told you that I need to give an solution to my existing network, please free to give me your recomendation.

regards.

[Wiyat Spain]

CORRECT ANSWER....

Dear All

After that I read it the before information that you recommend I spoke with other person where we discuss this problem and the only change that I do was.:

1. On the switch 3750 by default come enable by default that the load-balance will be run using src-mac

#show etherchannel load-balance
EtherChannel Load-Balancing Configuration:
        src-mac

I run the following command:

#conf ter
(config)#port-channel load-balance src-dst-ip
(config)#end
#show etherchannel load-balance
EtherChannel Load-Balancing Configuration:
        src-dst-ip

With this change automatically the traffic share between the three interfaces and I not have any more my problem 

Thank you for all..

[Wiyat Spain]

Dear, Jon Marshall

   Firstly thank you for reply.- What is your best recomendation to fix, correct my situation where right now the traffic that exist between the catalyst and 7200 Router is:

7206:Gi0/1   ------------------- C3750: Gi1/0/3:      970MB/Down

         Gi0/2   -------------------              Gi1/0/4       250MB/Down

         Gi0/3   -------------------              Gi1/0/5       150MB/Down

A. Now I have hight latency between Switch and Router, 400ms not all the time but when the traffic is on 970MB the latency going up.

B. I need to correct this situation and I expecting that with the port-channel I will be do it but isnt possible.

Please can you give me an examples or link with example to understand more clear what I need to do maybe with some example I can understand..