Ether channel load balancing

[CSCO11508096]

HI everybody,

today while reading about ether channel I come to know that in pagp or lacp (auto or desirable mode) we can check the no of packet sent and recieved at the individual interfaces configured in etherchannel.

by using command show pagp 1 counter

My question is how come we know the distribution of packet across each interface if etherchannel mode is on.

we have few servers that are replicating data between two sites,etherchannal is configured in on mode between these two sites. I need to know whether all the ports are distributing traffic equally or not.

Please help...

[daniel.dib]

Note that CEF by default does load sharing per destination which means that traffic load per link can vary a lot. Even if you do per packet the distribution will never be perfect. It also depends on which method you are using and if your traffic is between only two IPs or multiple IPs, between two MACs or multiple MACs and so on.

You can use the show etherchannel load-balance to see which method you are using. You can use the command test etherchannel load-balance to see which link would be selected depending on which IPs and MACs you use.

You can check the counters of the individual links to see how much traffic is going through them.

Also see this link for more information:

http://www.cisco.com/en/US/tech/tk389/tk213/technologies_tech_note09186a0080094714.shtml

Daniel Dib
CCIE #37149

[Peter Paluch]

Daniel,

Note that CEF by default does load sharing per destination which means  that traffic load per link can vary a lot. Even if you do per packet the  distribution will never be perfect. It also depends on which method you  are using and if your traffic is between only two IPs or multiple IPs,  between two MACs or multiple MACs and so on.

I am afraid you are talking about two different and unrelated things. CEF is concerned with IP packet routing; EtherChannel is concerned with frame switching. EtherChannel operation is not related in any way to CEF and is not influenced by the CEF load share settings (per-packet or per-destination). To CEF, EtherChannel is a single interface if it operates in Layer3 mode, and is totally invisible if it operates in Layer2 mode.

To Shashi - the signalling protocol used by an EtherChannel (PAgP, LACP or no protocol when using the "on" mode) has no influence on the load sharing ratio. As Daniel suggested, the easiest way to check the loading of the member interfaces is to simply check the interface counters. The show interfaces, show interface counters and especially show interfaces counters etherchannel are three commands readily usable for this purpose. In general, using the src-dst-ip mode of load balancing should provide for the best available traffic splitting.

Best regards,

Peter

[daniel.dib]

Yes, you are correct Peter. I was thinking of ECMP in this case.

Daniel Dib
CCIE #37149

[SJ K]

Hi all

Not my intention to hijack this thread, but this is the closest i can find around with the doubt i have in my mind between ip cef load-balancing and etherchannel.

Hi Peter,

Nice to see you here! Not sure if you remember me, but i sure remember you and the discussion with you on EIGRP and its algorithm - learn a great deal.

If you are still ever around... hope you get to this message...

q1) Can i check if the sequence of evaluating load-balancing for a particular network flow/packet is via this sequence (when ip cef and etherchannel is setup).

ip routing table (more then 1 path/route to the same destination exist) -> ip cef  -> ether-channel load-balance settings

Reason being is that I have 2 sites, each site has a pair of L3 switch stacked. (2 switch per stack)

The stack switches on each site are connected with 2 cables (1 cable on each switch) with ether-channel configured.

The stack switches has ip cef turn on.

The 2 sites communicate with each other via the L3 port-channel interface on the stack switch which are in the same subnet

Site1 stack switch (port-channel interface 192.168.1.252)  <----> Site 2 stack switch (port-channel interface 192.168.1.253)

The load-balancing for the etherchannel is set to src-dest ip.

================================

q2) The only traffic trans-versing this link, will be the communication between my db-server and standby which is a 1:1 src-dst pair.

So can i say that ->

Even if I have ip cef and turn on per packet sharing, to ip cef itself, the port-channel is only 1 exit interface and the load-balancing will not be based on per-packet sharing across the 2 physical cables;

but it will be base on the etherchannel load-balancing algorithm (src-dest ip) set.

Thus, my traffic above will always utilized 1 link in the port-channel.

Right ?

Regards,
Noob