LACP load balancing

[a.samuelsson]

I have a bundle of 4x10G.

One of the links have alot more traffic than the other

Te0/4/0/20             2.1G/ 21%     5.5G/ 55%    3898T/518.4M    9266T/1.3G  
Te0/4/0/21             2.0G/ 20%     3.7G/ 37%    3328T/515.2M    6820T/906.2M
Te0/4/0/22             2.1G/ 21%     6.8G/ 68%    4213T/537.3M   10977T/1.7G  
Te0/8/0/15             2.2G/ 22%     4.4G/ 44%    3451T/557.6M    7761T/1.1G

during peak hour it results in congestion on that link while the other links has space left.

Traffic running over these links are internet traffic with alot of flow but my suspisions are that it could be large GRE tunnels causing this.

With Juniper you can smooth out the difference between individual links by using "load-balance adaptive"

Is there any way of duing the same thing with Cisco ASR9K running 6.1.4

thanks in advance

Anders

[nkarpysh]

Hi Anders,
You are right - if we have some "fat" flow (e.g. GRE) it will be hashed to one link and over-utilize it. L3 Bundle by default uses 5-tuple (Src/Dst IP, Src/Dst L4 port, Router ID) if can find all these detail in the packet. It then generates hash at takes 8 bits to select the outgoing interface. May not be that granular for GRE as after IP header we have another IP header (no L4).

More details on balancing here:
https://supportforums.cisco.com/t5/service-providers-documents/asr9000-xr-load-balancing-architecture-and-characteristics/ta-p/3124809

To get around this, you may have to configure "cef load-balancing adjust X" command on the router. What it does is on the hash generated - 8 bits selected will move right by X, so you have chances of using a bit of different part of hash for balancing. You can try to vary X to see if it helps you to reach granularity.

HTH
Niko

[a.samuelsson]

ok, thanks
Do you know if this is sevice affecting or can I apply it on the run?

/anders

[nkarpysh]

You can apply it on the run - but I recommend to do it during non-peak hours first to see if distribution is ok or you might want to shift hash window more.

Niko

[senpai]

Hello Anders,
I am curious as to what command shows the bundle traffic stats as you have shown in your question.

thanks

[a.samuelsson]

Hi

It is not a bundle command but a pure monitor interface of each individual link

/anders