Load balancing across WAN links

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Jul 5th, 2007
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I have two WAN links that I would like to load balance traffic across using EIGRP but both links come in on a switch card and are separated using VLANS. I know with EIGRP its important to have the delay and bandwidth set to accomplish load balancing.


My question is should I place the bandwidth and delay on the VLAN interface or on the Fast Ethernet interface???

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paolo bevilacqua Thu, 07/05/2007 - 07:31
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Excuse me, have you ever used the variance supposed functionality? Be aware that beside requiring special configuration, it never worked in practice, and has no know implementation in customers network.

paolo bevilacqua Thu, 07/05/2007 - 07:32
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Hi,


please don't change the EIGRP default values before determining a need for that. In a layer-3 switch, all the IP level configuration is made at the VLAN interface.

kwillacey Thu, 07/05/2007 - 07:35
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Well it is actually a router with a switch card so I am to assume I should place the statments on the VLAN interface then.

paolo bevilacqua Thu, 07/05/2007 - 07:55
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Yes. Under the physical interface, you only configure to which VLAN it pertains, and that's it.


Hope this helps, please rate post if it does!

kwillacey Thu, 07/05/2007 - 08:05
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So to clarify my config should reflect below:


int vlan 2

ip address 1.1.1.1 255.255.255.0

bandwidth 100

delay 100


int fa0/0/0

switchport access vlan 2


the bandwidth and delay statements should not go on the int fa0/0/0

paolo bevilacqua Thu, 07/05/2007 - 14:23
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Hi,


As I said above you need not to configure bandwidth and delay and your eigrp will work fine. The parameters influence the metric compute, thing that you don't necessarily need to do.

Edison Ortiz Thu, 07/05/2007 - 15:55
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Kelvin,


I agree with Paolo regarding the EIGRP configuration. Before changing the metrics, can you post a show ip route [network.address] from a route being received via the 2 VLANs ?


This way we can recommend if you need the bandwidth and delay statements in the configuration. Playing with these metric without checking your initial configuration, can create future problems.


And to answer your question, all metric values should be placed on the interface running the protocol. The interface running the protocol must hold an IP address. Per your previous post, a FastEthernet interface is only layer 2 - the SVI (Switch Virtual Interface) is the one holding the L3 information. However, please post the show ip route before proceeding.


Thanks


jay77jay77 Fri, 07/06/2007 - 01:43
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As said, i will suggest not to change any metrics, as both the interfaces are similar and metrics will be the same and this will let eigrp to loadbalance the traffic.


Also as you told, the interfaces are on the same router, how does it terminate at the remote end... on the same router??

If so, you may test out per-packet loadbalancing for complete 50/50 load balancing.


If not eigrp will do load balancing per destination, whic lead to uneven loadbalancing..


Note: per packet loadbalancing consumes more processor cycles...


So the selection configuration of perpacket or perdestination depends on the traffic pattern across the two sites.



Cheers!


paolo bevilacqua Fri, 07/06/2007 - 02:36
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hello jay,


please note, per se, eigrp or other routing protocols do not decide the type of load balancing done, even if some documentation may lead you to think so. Layer3 switch have their own balancing algos that are basically similar to CEF in routers. There are no process cycles in layer3 switches as the routing decision is made in hardware.

I also suggest to not enable per packet load-balacing as it may lead to out-of-sequence arrival.



jay77jay77 Sun, 07/08/2007 - 18:26
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hi gibson,paolo,


do u see out of sequence issue, even on parallel links terminating on the same physical routers at both ends?


Cheers!

paolo bevilacqua Mon, 07/09/2007 - 01:23
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Once again, with regard to the "unequal cost path balancing of EIGRP":


1. It is not what the original poster asked about. In no occasion he said the links were of different speed or topology.


2. Despite any document claiming so, is not proved to work and has no known implementation in customer networks.


3.It can introduce instability and and is not recommended by Cisco TAC.


You will find that people that talks about it, has just read it on the documentation and never tried it, much less using in a real live network.

kwillacey Mon, 07/09/2007 - 04:29
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The links are of the same bandwidth, at first only one end was load balancing but then I applied the bandwidth statements on the other end and it started to load balance.


I had put the bandwidth statement on the fastethernet interface and nothing happened and then I had put it on the vlan interface and it started to load balance so I guess I got my answer.

paolo bevilacqua Mon, 07/09/2007 - 05:58
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Hi,


That is consistent with the indications we gave you about routing paramenter to be configured under VLAN interface and not physical interface.


Would you consider rating useful posts using the scrollbox below? In fairness this thread would benefit from it, having got a low rating for no reason whatsoever.

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