Port Channeling and redundancy

[Joris Kemperman]

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

[Mark Malone]

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?

[Joris Kemperman]

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?

[Mark Malone]

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

[Joris Kemperman]

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.

[Mark Malone]

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,

[Joseph W. Doherty]

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.