ā11-04-2023 12:26 PM - edited ā11-04-2023 12:30 PM
My company's data center is currently using a Cisco C9500-24Y4C connected to an ISP router x670 extreme.
We've configured a port-channel with 4x 10G ports, divided into two VLANs (VLAN2 and VLAN3).
Our BGP configurations are identical on both sides, and we've confirmed that the connection is established.
However, we've encountered an issue where it seems like traffic is only utilizing one of the four interfaces in the port-channel,
and we're not achieving the desired load balancing. Can you please advise on what steps or configurations may be missing?
Thanks in advance,I will appreciate your help.
Solved! Go to Solution.
ā11-13-2023 01:38 AM
@Baratheon , that is correct. Each device can only control which link to forward the frames onto. The X670 would also require a change to it`s etherchannel load-balancing as the default seems to be source+destination MAC addresses. Exos configuration is unfortunately not something I am familiar with. Your ISP can likely assist you with the X670 configuration if you describe that you wish to load-balance the etherchannel based on source and destination port numbers. This article describes exos etherchannel configuration and load-balancing options: https://extreme-networks.my.site.com/ExtrArticleDetail?n=000002358.
Your command output confirms that your etherchannel is bundled as it should and that this is an etherchannel load-balancing issue.
ā11-04-2023 12:36 PM
Can I see the bgp config on both sides.
Thanks A Lot
MHM
ā11-05-2023 10:22 AM
Sure, I will provide you with the detailed BGP configurations for both sides. I'll gather the necessary information and share it with you shortly. Thank you for your assistance. Your help is greatly appreciated.
ā11-07-2023 09:52 AM
ā11-04-2023
01:46 PM
- last edited on
ā12-15-2023
01:56 PM
by
Translator
This sounds like a etherchannel polarization issue. The default load-balancing algorithm for catalyst 9k switches only uses source mac address for hashing. Meaning that if your traffic comes from the same mac address it will be sent over the same single link. You can configure this with the
port-channel load-balance
command. To achieve the most even load balancing across the port-channel you should select the values that will vary the most for the traffic. Here are the available options for the
port-channel load-balance
command on the 9500:
Switch(config)#port-channel load-balance ?
dst-ip Dst IP Addr
dst-mac Dst Mac Addr
dst-mixed-ip-port Dst IP Addr and TCP/UDP Port
dst-port Dst TCP/UDP Port
extended Extended Load Balance Methods
src-dst-ip Src XOR Dst IP Addr
src-dst-mac Src XOR Dst Mac Addr
src-dst-mixed-ip-port Src XOR Dst IP Addr and TCP/UDP Port
src-dst-port Src XOR Dst TCP/UDP Port
src-ip Src IP Addr
src-mac Src Mac Addr
src-mixed-ip-port Src IP Addr and TCP/UDP Port
src-port Src TCP/UDP Port
You can read more about this here: https://www.cisco.com/c/en/us/support/docs/content-networking/load-balancing/215112-troubleshoot-polarization-in-port-channe.html
ā11-04-2023 03:33 PM
@TorbjĆørn is completely correct that a "worst" case LB algorithm choice can lead to poor, or even no, traffic distribution across links. LB based on just one attribute, like src-mac, often bumps in to worst case traffic distribution. In general, LB algorithms that use multiple attributes, like src-dst-mac or src-dst-ip, often do well, in many cases. Also keep in mind, sometimes the best LB algorithm choices depends on flow direction; i.e. the two sides need not use the same LB algorithm.
As to whether you've bumped into "polarization", from what's posted in OP, unsure we can determine if that's happening.
"Polarization" isn't new, nor limited to just Etherchannel. You might find this 2013 (6500) CEF Polarization TechNote interesting.
ā11-05-2023
10:32 AM
- last edited on
ā12-15-2023
01:48 PM
by
Translator
Thank you for your response.I've attempted to use the
port-channel load-balance
command on the Catalyst 9500 switch as per your suggestion, but it hasn't yielded any noticeable results. Would providing you with the detailed configuration information be helpful in assisting me with this issue?
ā11-05-2023 12:03 PM
Detailed configuration on the port-channel interface and bundled interfaces would be useful. Since you say that only one port is used for traffic, is the port-channel operational on both ends? Can you see all expected interfaces as "In portchannel" in the output of "show etherchannel summary"?
Note that etherchannel load-balancing is directional since each switch can only control which links it sends frames on. Depending on the traffic you are forwarding across the port-channel this might be of importance for whether configuring loadbalancing on the 9500 would make a difference.
ā11-07-2023
09:57 AM
- last edited on
ā12-15-2023
01:49 PM
by
Translator
ā11-05-2023 10:39 AM
Thank you for your response!!At one point, I had a suspicion that the lack of load balancing might be due to the network traffic not exceeding 2G to 3G, while my configuration utilizes a 4x10G PortChannel. As a result, it seems that the traffic is concentrated on one port, which could explain the absence of load balancing. What are your thoughts on this theory?
ā11-06-2023 03:32 AM
Hello @Baratheon ,
load balancing should happen regardless of traffic volume and it just requires that multiple traffic flows with enough diversity are being sent.
A single traffic flow will always use a single link based on the hashing results of its key fields ( source IP , dest IP for IP traffic with default settings)
Hope to help
Giuseppe
ā11-07-2023 10:02 AM
ā11-07-2023 10:27 AM
You have no control over the other side's LB unless you can configure that device.
From you recently provided configs, it all looks pretty vanilla. Next would be to confirm all the links are active in the Etherchannel bundle. Also, confirm LB algorithm currently being used.
ā11-13-2023 12:48 AM
@Giuseppe Larosa I will try the valuable suggestions you provided. Thank you!!
ā11-06-2023 04:57 AM
As @Giuseppe Larosa replied, traffic volume isn't a factor with LB beyond more concurrent flows might be distributed across multiple links.
In a @TorbjĆørn recent reply, Etherchannel configuration information, and some stats, was asked for. That could be very helpful.
@MHM Cisco World has asked for additional BGP information and has noted BGP, by default, will not use multiple paths. Although that's correct, an Etherchannel is always seen as one link, so it's unclear how BGP config would matter, but it wouldn't hurt to provide that information too.
Personally, within OP, you describe assigning two VLANs to this Etherchannel, which possibly makes the information @TorbjĆørn requested, the most important.
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