Problem with etherchannel between 2 3550 FXs

I have a 3550's in different buildings with ~2km of multimode fiber between them. Until we upgrade to singlemode, we want to use etherchannel to get us to at least 400mbps.

The link works great, but can't seem to get more than 100mbps over the link. I will disconnect what appears to be the active channel and one of the other ones picks up no problem.

Version:Cisco Internetwork Operating System Software IOS (tm) C3550 Software (C3550-I9Q3L2-M), Version 12.1(11)EA1, RELEASE SOFTWARE (fc1)

Each switch is configured the same and here is a config snipit:

no service pad service timestamps debug uptime service timestamps log uptime no service password-encryption ! ip subnet-zero ! spanning-tree extend system-id ! interface Port-channel1 description EtherChannel SM-3550-FX to GH-3550-FX no ip address ! interface FastEthernet0/1 description EtherChannel 1 Port 1 switchport trunk encapsulation dot1q no ip address channel-group 1 mode desirable ! interface FastEthernet0/2 description EtherChannel 1 Port 2 switchport trunk encapsulation dot1q no ip address channel-group 1 mode desirable

interface FastEthernet0/3 description EtherChannel 1 Port 3 switchport trunk encapsulation dot1q no ip address channel-group 1 mode desirable ! interface FastEthernet0/4 description EtherChannel 1 Port 4 switchport trunk encapsulation dot1q no ip address channel-group 1 mode desirable

Is there something silly and simple I am missing? Thanks for any help.

Reply to
Who knows?
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In article , Who knows? wrote: :I have a 3550's in different buildings with ~2km of multimode fiber between :them. Until we upgrade to singlemode, we want to use etherchannel to get us :to at least 400mbps.

:The link works great, but can't seem to get more than 100mbps over the :link.

In the configuration portion you included, you did not have any command explicitly setting the mechanism for a selecting particular link for any one connection.

For any constant number of active links, the choice of links for any one connection is deterministic, based upon the source and destination MAC addresses. Essentially it takes some number of the final bits of each of the source and destination MACs, performs a logical operation on them (e.g., XOR), and the numeric result selects which of the links is used.

You get to choose which logical operation you want, but for any one source + destination pair, the result is going to be constant within the chosen operation.

The implication of this is that if your traffic is all between two fixed MACs (e.g., if there is a routing interface on either side of the link) then the traffic would all go over one link. Or if the sources differ but the destination is the same each time, and you happen to have chosen the logical operation that ignores the source MAC, then it'll end up going over the same link...

EtherChannel is not really designed for "load-balancing" as such: it is more a way to allow multiple connections (between different systems) in parallel.

If I recall correctly, you can also select per-packet load balancing, but then you run the risk that packets will arrive out of order, which might matter very little or might matter a lot in some cases. (e.g., for TCP with Selective ACKs turned on, it might be fine, provided you aren't fragmenting packets; but for multimedia streaming out-of-order packets can be big trouble.)

Reply to
Walter Roberson

So what do I need to do in order to get these 4 links I have to combine together to get ~400mbit? Is there some bit of configuration that I am missing?

Reply to
Who knows?

In article , Who knows? wrote: :So what do I need to do in order to get these 4 links I have to combine :together to get ~400mbit? Is there some bit of configuration that I am :missing?

It looks like the options are more limited for the 3550 than what I was indicating before... no XOR for example.

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Please read that section over to see why if you only have one source and destination pair, you are going to end up using only one of the links of the group.

Beyond that... you could read the cisco documents about per-packet load balancing. There are several ways of doing it such as via OSPF or CEF. I don't know which of those are supported on the 3550. You wouldn't use EtherChannel for those methods, though.

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Reply to
Walter Roberson

The key thing is that with etherchannel any one unidirectional flow will take one transmission port in the bundle.

The definition of "flow" can be changed in some platforms and some software and can include various combinations of MAC and IP addresses and port numbers.

In a many environments e.g. a server at one end and multiple workstations at the other you do get effective load balancing, however if for example you are backing up one server to another across such a link then you will not usually (ever?) get load balancing.

As Walter says you may be able to configure per packet load balancing if you configure routed links but this will involve re-addressing.

A google search [gigabit multimode distance] though reveals

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"With MRV's GMX technology, Gigabit Ethernet Multimode fiber-optic networks can extend up to 2km. This allows for the use of high-speed backbone protocols over fibers that were originally used for FDDI rings."

Doesn't look cheap though. Not so bad $1500. Probably per end.

I have no knowledge of the performance of the GMX equipment at all. Caveat emptor.

Reply to
anybody43

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