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Load Balancing

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Load Balancing

We are having issues with load balancing in Docsis 2 modems. The wired only cable modems change channels and then the customer router loses connection and requires a reboot of their device. Previously I could find some modems where it happened at 5 minutes on the dot.

1. Is there ANY way to log this activity so we can see it happening?
2. What are all the different load balancing methods and their affect?

Docsis-group? Is this v2 v3 or all?
cable load-balance docsis-group 8100
downstream Integrated-Cable 8/1/0 rf-channel 0-3
downstream Integrated-Cable 8/1/1 rf-channel 0-3
downstream Integrated-Cable 8/1/4 rf-channel 0-1
upstream Cable8/1/0 0-2
init-tech-list 1-4
interval 300

Is this just upstream bonding for D3? Or does it affect D2 somehow as well?
cable upstream bonding-group 80
upstream 1
upstream 2
attributes 80000000

Are there other methods? On the 7200 mc28's it was very different

Part 2.. Do Docsis 3 modems

Part 2.. Do Docsis 3 modems handle load balancing, channel changes etc without impacting service? What if a channel is bad will it wean it without the client knowing? I know 2.0 is a brutal move although it seems like DS channel changes were smoother.

Load-balance! what a topic!!!

Load-balance! what a topic!!!

Let me have a crack, hopefully I don't make too many mistakes

"cable load-balance docsis-group" = docsis 2.0 load balancing.
You would typically enter this config manually.
(Or if desperate, you can use this command to auto build it : "cable load-balance d20 glbg auto-generate")

This balancing applies to D2 modems only

If you balance on modem count ("method modems"), then the balancing happens only at registration time. This should be pretty safe, as you wont be disrupting any active dataflows.

Or, if you balance on load ("method utilization") then the balancing will happen during periods of high traffic. This is a bit more risky if your modems don't handle the DCC or UCC commands smoothly. Especially since the modems getting moved are typically the busy ones.

From memory, you can can experiment with DCC and UCC like this :
test cable dcc xxxx.xxxx.xxxx ....
test cable ucc xxxx.xxxx.xxxx ....


Then there is a separate docsis 3.0 load balance.

This config is autogenerated by the CMTS, based on information in the fiber-node stanzas etc
Confusingly, this load-balance config typically wont show show up in the "show run" unless you have customised it.

Docsis 3.0 load balance works by spreading D3 modems across the available bonding groups in the mac domain.

For example, consider a mac-domain that has 32DS. If you have 8x4 modems, you would typically have created 4 x 8DS bonding groups. And you will want the modems to spread across these groups.

If you don't activate docsis 3.0 load balance, I believe the CMTS will just try to spread the modems across the available bonding groups at registration time by randomising the offered RCCs (you can see a list of RCCs with "show cable mac-domain cable 5/0/0 rcc")

If you have docsis 3.0 load-balance enabled, the CMTS will try to intelligently balance modems across bonding groups :
* method modems - operates at registration time by offering the RCC with lowest modem count
* method utilisation - operates at periods of high load, uses DBC commands to dynamically move modems between bonding groups

You can experiment with DBC like this :

test cable dbc xxxx.xxxx.xxxx init-tech <1-4>
test cable dbc xxxx.xxxx.xxxx rcc
test cable dbc xxxx.xxxx.xxxx done

Method 4 is the fastest / least disruptive, method 1 is the slowest / most disruptive.
Pretty sure that D3 dynamic load-balance only uses method 4


One of the best tips for understanding load-balance is to use "show run all | begin load-balance".
This will expose all the load-balance settings, making the config a lot more understandable.


You asked if "cable upstream bonding-group 80" is for D3 or affects D2 as well.
It only affects D3.

You asked about different load balance methods.

I reckon there are 5 different methods :

The stuff I have been talking about above is docsis 2.0 General Load Balance Group (GLBG) and docsis 3.0 GLBG.
These apply to all modems.

If you want to have different balancing for different modems/customers, you can create D2 and D3 Restricted Load Balance Groups (RLBG).
eg maybe you want to offer different balancing to business vs residential customers.

And then there is the super old / depreciated "Cisco load balancing", which was applied inside the mac-domain eg
interface cable 5/0/0
cable load-balance group 1
cable upstream X load-balance group 1


hope that helps!