Unequal cost Paths Load Balancing with Eigrp

[leonardo-f]

Hello Guys!

I have a Branch office router (R1) with  two  wan links to my server farm, the first is a Frame Relay link with a CIR of 128k, the second is a satellite link with a CIR of 256k configured through a tunnel, each with a different service provider and different end routers (R2 and R3), I would like to share the load equitably between the two links.  (Attachment: Netwok Diagram)

I used the Variance 2 command on R1 but the load sharing proportion of outgoing traffic  between the two links is about 90/10 (90% over the FR Link 10% over the sat link) and all the incoming traffic only uses the FR link.

The sat link has a  greater delay than the FR  so i adjust the delay values at the interface of the sat link and the proportion was better (about 70% - 30% )I would like to know the best way to implement load balancing according to my situation in the most equitable way to both outgoing and incoming traffic.

SH IP EIGRP TOPOLOGY

IP-EIGRP Topology Table for AS(100)/ID(10.255.54.18)

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,

       r - reply Status, s - sia Status

P 0.0.0.0/0, 1 successors, FD is 10642432

        via 10.255.54.17 (10642432/28160), Tunnel454

        via 10.1.54.17 (20512256/768), Serial0/1/0.454

P 10.1.54.16/30, 1 successors, FD is 20512000

        via Connected, Serial0/1/0.454

P 10.255.54.16/30, 1 successors, FD is 10639872

        via Connected, Tunnel454

P 10.204.54.0/24, 1 successors, FD is 28160

        via Connected, FastEthernet0/0

* SH IP EIGRP NEIGHBORS

sh ip eigrp neighbors

IP-EIGRP neighbors for process 100

H   Address                 Interface       Hold Uptime   SRTT   RTO  Q  Seq

                                            (sec)         (ms)       Cnt Num

0   10.255.54.17            Tu454             14 06:02:51  690  4140  0  6949981

1   10.1.54.17              Se0/1/0.454       14 06:09:17   37  1140  0  302302126

[Kelvin Willacey]

Are you saying that one end has one router with both links and the other end has a router for each link? If that's the case only one direction can load balance traffic, unless there is another routing device behind the two routers.

[leonardo-f]

Thats correct one end have 1 router with two links and the other end have 1 router for each link

[Mohamed Sobair · Accepted solution]

Hello,

I couldnt view the attached file, however , as a fundamental statement, is that Loadbalancing is performed outbound direction on the router, you cant influence inbound loadbalancing on the local router, but you can have some sort of loadsharing.

You can spilit your subnet at the DR main Site of the Servers, and lets R2 and R3 sends different subnets to R1 along with the main subnet. This way , you can have loadsharing inbound.

Regards,

Mohamed

[dslice]

In case you didn't know it, EIGRP is responsible for installing the routes in the rib, but doesn't directly affect the actual percentage of traffic forwarded through each path. That's done by the forwarding code (normally CEF) and can be influenced by the metrics and thus the load share value set for each path, but it's hardly exact. Since CEF can use different criteria for building CEF entries (I think default for most trains is source/dest) which means the characteristics of the actual traffic can change the proportions.

You can and should set the metrics to make the ratio for the load share values match what you want but don't be surprised if the results aren't exactly what you want. Also recognize that it's possible you'll end up with out of order packets for your traffic (depending on your CEF load balancing behavior) which could possibly impact your flow performance depending on how tolerant your applications are to this.

Sent from Cisco Technical Support iPad App

[Marwan ALshawi · Accepted solution]

well this design might lead to out of sequence TCP or asymmetrical routing why you don't use load sharing using PBR with IP sla to make it reliable to load share the source destination traffic selectively

or just use it in active standby

or the other option which is a bit more complicated if you never done it using Performance Routing PfR where you can loadbalance 50/50 or 70/30 based on link utilization for example

http://docwiki.cisco.com/wiki/PfR:Solutions:EnterpriseData

https://supportforums.cisco.com/docs/DOC-8353

Hope this help

[Joseph W. Doherty]

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Posting

EIGRP unequal load balancing easily configured R1.  To do similar on R2 or R3, believe you need to make one of the two routers gateway for all outbound traffic and then account for the LAN hop between them also insuring redirect are not provided to the hosts.  (You might also use GLBP on R2 and R3 which can also be configured for unequal/proportional usage.)

EIGRP will proportionally route individual flows (unless you enable per packet load balancing - not recommended).  As such, at any one time actual link load usage is likely not to match expected load balancing although long term average usually does.  (Similar issue with GLBP although is proportions by host MAC and as such is more likely not to meet short term or long term proportions unless all the sending hosts transmit about the same amount of traffic.)

OER/PfR that supports PIRO could be implements on one or both sides.  It, unlike routing or gateway load balancing, dynamically load balances.  If used, you shouldn't need to use routing or gateway load balancing, although since OER/PfR takes some time to make adjustments, I've found routing and gateway load balancing provides a course load balancing which OER/PfR "tunes".  Even it, again without packet-by-packet, will not balance a single flow.  (NB: there's much more to OER/PfR's balancing capabilities.)