07-16-2009 12:53 PM - edited 03-06-2019 06:48 AM
I had a colleague tell me that when you form a Portchannel with Ethernet interfaces on IOS that IP multicast is not equally balanced across the links of that group. Is that true, and can someone point me in the direction of docs that support that?
07-16-2009 01:54 PM
Depending on the switch you are using you will have to setup what type of load balancing is done on the etherchannel link. Here is the global command:
port-channel load-balance {src-mac | dst-mac | src-dst-mac | src-ip | dst-ip | src-dst-ip | src-port | dst-port | src-dst-port | mpls}
Of course if you are load balancing based on only src-ip/dst-ip (if a single multicast server) then multicast will not be load balanced.
Reference: http://www.cisco.com/en/US/tech/tk389/tk213/technologies_tech_note09186a0080094714.shtml
07-17-2009 05:16 AM
So he was correct. Does anyone know of a good way to balance the load with multicast traffic?
07-17-2009 05:54 AM
Hello Robbie,
actually modern switches can use different algorithms with different type of traffic
see the example above taken from a C6500
sh etherchannel load-balance
EtherChannel Load-Balancing Configuration:
src-dst-ip
mpls label-ip
EtherChannel Load-Balancing Addresses Used Per-Protocol:
Non-IP: Source XOR Destination MAC address
IPv4: Source XOR Destination IP address
IPv6: Source XOR Destination IP address
MPLS: Label or IP
multicast is still IPv4 packets so a source exor destination should be enough
You can see options with
port-channel load-balance ?
dst-ip Dst IP Addr
dst-mac Dst Mac Addr
dst-port Dst TCP/UDP Port
mpls Load Balancing for MPLS packets
src-dst-ip Src XOR Dst IP Addr
src-dst-mac Src XOR Dst Mac Addr
src-dst-port Src XOR Dst TCP/UDP Port
src-ip Src IP Addr
src-mac Src Mac Addr
src-port Src TCP/UDP Port
Hope to help
Giuseppe
07-17-2009 07:23 AM
So what could I do when I have a heavy flow between a set of hosts? Since both the source/dest macs, IPS, and ports are the same, is there anyway to get the router to split it across the second link in the bundle?
07-17-2009 10:39 AM
Hello Robbie,
the operation is an exor of last significant digits of source IP address and destination IP address.
In case of multicast flows the destination is the multicast group address and the source is the source address.
So yes a given (S,G) multicast flow is forwarded out a single link of the bundle.
if you have multiple sources of G groups with a wise choice you can get some load balancing.
If you have routers or L3 switches you can consider to use the links as independent L3 links.
And then you can use ip multicast multipath command in global config
see
http://www.cisco.com/en/US/partner/docs/ios/ipmulti/command/reference/imc_03.html#wp1037261
or
http://www.cisco.com/en/US/docs/ios/ipmulti/command/reference/imc_03.html#wp1037261
Edit:
this is still flow based so no real advantage over a L2 etherchannel bundle.
Hope to help
Giuseppe
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