04-23-2017 11:52 PM - edited 03-08-2019 10:18 AM
Hi all,
From what i have understood, port channeling gives me redundancy options and double the amount of speed, but tests show a completely different picture.
I have two Catalyst 3750-X stacks, and want to replace a single connection between them into a double/redundant one.
- On each device i created two LACP port channels named Po1, each linking two 1Gbps ports on two switches
- Po1 is set to 802.1Q Trunk, all Vlans
When i insert all 4 cables, i have connectivity but:
1) When i pull one cable (and leave the other one connected), the link is down. There is no redundancy
2) When i put a lot of data through the link, i noticed that one port is beeing heavily utilized while the other one is almost completely idle. Seems like i only have 1Gbps throughput instead of 2Gbps.
What am i doing wrong?
Best regards,
Joris
04-24-2017 12:13 AM
Hi the traffic can be altered you need to test the the etherchannel load balance distribution it doesn't always work straight off the bat you may have to manipulate it and test the traffic pattern of what link its crossing
see this doc for full explanation below , src-dst-port works well for use and utilizes all links
like below
(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
mpls Load Balancing for MPLS packets
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
vlan-dst-ip Vlan, Dst IP Addr
vlan-dst-mixed-ip-port Vlan, Dst IP Addr and TCP/UDP Port
vlan-src-dst-ip Vlan, Src XOR Dst IP Addr
vlan-src-dst-mixed-ip-port Vlan, Src XOR Dst IP Addr and TCP/UDP Port
vlan-src-ip Vlan, Src IP Addr
vlan-src-mixed-ip-port Vlan, Src IP Addr and TCP/UDP Port
#test etherchannel load-balance ?
interface Port-channel interface
ip IP address
ipv6 IPv6
l4port Layer 4 port number
mac Mac address
mixed Mixed mode: IP address and Layer 4 port number
mpls MPLS
see this doc
http://packetpushers.net/understand-etherchannel-load-balancing-catalyst-switches/
1 1) When i pull one cable (and leave the other one connected), the link is down. There is no redundancy
Is the link not up/up in the PO already ? are you seeing anything irregular in logs , stp issues or anything else?
04-24-2017 12:26 AM
Thanks for your quick response Mark, much appreciated.
About the balancing:
I only have these options:
(config)#port-channel load-balance ?
dst-ip Dst IP Addr
dst-mac Dst Mac Addr
src-dst-ip Src XOR Dst IP Addr
src-dst-mac Src XOR Dst Mac Addr
src-ip Src IP Addr
src-mac Src Mac Addr
Which option would suit us best? Imho all traffic should be balanced, not just one protocol or source address.
About the redundancy:
I do not see any errors, but maybe i'm looking in the wrong direction. Is it correct, that 'normally' links are redundant once they are in a port-channel?
04-24-2017 12:52 AM
Hi
I would go with either src-dst-ip if port is not available that should work well for you
2 Yes they should be all up in bundled state and ready , you can check this with ....
sh etherchannel summary .... your links must show a P beside them for bundled and up , the Po should state either RU or SU meaning switched up or routed up for layer 3
100 Po100(RU) - Te1/5/4(P) Te1/5/5(P)
If your not sure post what you see and we can go through it
04-24-2017 01:05 AM
Mark thanks a lot again. :-)
Is this just a 'setting' i can configure for this specific port-channel Po1m and for specific IPs? Or is this something that i have to enable and will work on all port-channels?
This example shows me just how to enable it i think? I do not see an example of them specifying to loadbalance ip x.x.x.x to y.y.y.y. on Po1.
Im looking for a good example how to use the commands, but can't really find a proper one.
04-24-2017 01:22 AM
Hi
personally I wouldn't go that granular doing LB for a particular ip set you want it to be dynamic so whenever anything else passes the port-channel it fillows the same rules , I would enable it globally at and then test that both links are being used and traffic is passing both links rather than just 1
1 port-channel load-balance src-dst-ip
Then
2 Check the flow of traffic
test etherchannel load-balance interface port-channel x
or
test etherchannel load-balance ip 1.1.1.1 2.2.2.2 (as example)
The doc I originally posted explains the hashing bit in packetpushers but it can be bit complicated if not used to it , this is another doc with couple of other links that may help explain it better below
You could also just set it up with the new load balance and send a ;load of traffic to multiple destinations and see if the packet counters are increasing in both interfaces when you do a show ip interface x/x
https://supportforums.cisco.com/document/21011/how-configure-giga-etherchannel-xor-algorithm-switch-order-achieve-load-balancing
so example my 6500 core VSS for campus prod traffic uses the below only configured globally , this tells both switch to base its flows on the source and destination ports ,, works fine , I have in some cases up to 4 links in my portchannels
xxxxxxx#sh run | i load
platform ip cef load-sharing ip-only
port-channel load-balance src-dst-port
xxxxxxxx#sh int po5
Port-channel5 is up, line protocol is up (connected)
Hardware is EtherChannel, address is 0008.e3ff.fd90 (bia 0008.e3ff.fd90)
Description: xxxxxxxxxxds2 Po5
Internet address is xxxxxxxxxxx
MTU 1500 bytes, BW 4000000 Kbit, DLY 10 usec,
04-24-2017 05:27 AM
From what i have understood, port channeling gives me redundancy options and double the amount of speed, but tests show a completely different picture.
A dual port-channel provides twice the aggregate bandwidth, but also keep in mind individual flows only use one link.
Even with multiple flows, port-channel does not take into account link loading, so one link can be oversubscribed while another is dormant.
As Mark has noted, the load balancing algorithm can be crucial to obtaining the best usage of your multiple links.
On average (with optimal load balancing), expect about a 50% bandwidth increase using dual link port-channel.
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