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bryandizon
Beginner

How to load balance effectively on different delays on links thru EIGRP

Hi Everyone,

I'm in a bit of dilemma here, how can i effectively load balance my network traffic by eigrp, voice and data, on unequal quality links. To clarify, i have two links with different delay (due to the ISP) but same bandwidth. By default, eigrp will route all our traffic to the best link and the other will occasionally be used. To maximize our links what we did is use route-maps for data traffic to use the link with higher delay and leave the other traffic (voice) to the low delay link.

One problem with the route-maps, if the link with high delay would go down, we have to manually remove the route-map on the interface, i would prefer an automatic way of doing this, and by default eigrp would re-converge but the problem if we leave eigrp on default all our traffic will be routed to the low delay link.

If this has been answered before, I apologize and please redirect me to those post.

Thanks and appreciate any help.

Bryan

1 ACCEPTED SOLUTION

Accepted Solutions
Daniel Frey
Cisco Employee

Your data and voice traffic are on different subnets?    If so, you could use offset-list in EIGRP to make the metric higher (for data traffic subnets) on the low latecy ISP.   This would provide for automatic failover.   Would be good to set the offset-list so that the other backup link is a feasible successor.

-Dan

View solution in original post

15 REPLIES 15
boss.silva
Beginner

Hello,

You can use the variance command:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a008009437d.shtml

Regards,

Bruno Silva.

Marwan ALshawi
Advisor

Hi Bryan,

as mentioned above by Bruno with the variance command EIGRP can give you load balancing over unequal cost Paths

but in your case using VOIP i really do not recommend you to use load balancing and even worse you have the links with different bandwidth

what you did mention about using route-maps i am assuming you mean using route-maps for policy based routing PBR to enforce VOIP to go one way and Data the other

and you are right by default PBR by it is self will not automatically switch over due to link or path failure

however PBR can be very useful to your case if yo used in conjunction with IPSLA which is called reliable PBR

where you can send icmp traffic source from WAN  interface 1 going to next hope WAN 1 and if the icmp fail then the PBR will send the traffic over the other interface/WAN link

have look at the bellow example, ignore the NATing part and just focus on the PBR with IP SLA,

https://supportforums.cisco.com/docs/DOC-8313

HTH

if helpful Rate

bryandizon
Beginner

@Bruno - Thanks for the reply, appreciate it, I already looked into the variance command and it may have a use in the future.

bryandizon
Beginner

@marwanshawi - Thanks for the reply and appreciate it, I would be looking more into the reliable PBR and let you guys know.

The load balancing in this case is not implemented per packet but per flow, so  you should not experience the problems to do with jitter and out of  sequence packets as you would if the load balancing were routed per packet over the two links

You should really be alright to use eigrp with variance and bandwidth set correctly on the links in order to utilize the capacity of both links.

@chris - Thanks for the response, I'll look into it as well.

Daniel Frey
Cisco Employee

Your data and voice traffic are on different subnets?    If so, you could use offset-list in EIGRP to make the metric higher (for data traffic subnets) on the low latecy ISP.   This would provide for automatic failover.   Would be good to set the offset-list so that the other backup link is a feasible successor.

-Dan

View solution in original post

@daf - Thanks for the reply, yes, data and voice are on different subnets, the offset-list seems interesting and would simplify my configuration by not applying route-maps on the routers. Would this work if I have a two router setup. Refer to the diagram below, apologies for the crappy diagram.

                                                       Head Office

                                                         /           \

           low delay (voice preffered)        /               \     higher delay (data preffered)

                                                     /                   \

                                                  R1                   R2

                                                   |                       |

                                                   |                       |

                                                 SW1========SW2     etherchannel between SW1 and SW2

                                                   |      \         /      |

                                                   |         \   /         |

                                                   |       /        \      |

                                                   |   /               \   |

                                                ASW1              ASW2    access switch to clients

Brian,

Offset-lists will work in the diagram you have posted.   If the EIGRP domain is only on the WAN links, then you could setup two HSRP groups on the LAN.  First HSRP group can be used for voice and provide a preferred Gateway for voice clients on R1.  Second HSRP group VIP on R2 can be used as a preferred gateway for data clients. 

- Dan

Dan,

Both SW1 and SW2 have EIGRP as well (these are 3750's), also we have HSRP on SW1 and SW2 for the default gateways of the PCs and phones.

Would it work if we apply the offset list on the 3750's to influence the EIGRP of the voice subnets to R1 and data to R2 respectively?

Thanks,

Bryan

Are your devices EIGRP peers accross the WAN like a IPSEC/GRE VPN across the WAN or is this a MPLS VPN where the SP is redistributing EIGRP into MPBGP?  If there any redistribution points in the network the EIGRP metrics will need to be set during redistribution.   If your network is EIGRP end to end, then offset lists will work including the 3750 switches.

Dan

I tested it on our lab mirroring the production network and it worked!

What I did is match the Data subnets in an access-list, placed the offset on R1's EIGRP going out the segment connected to the LAN. Same for Voice, match them in an access-list, placed the offset on R2's EIGRP going out the segment connected to the LAN.

I ran tracert to verify the path from the test PC, did a continuous ping then caused a failure, once eigrp re-converged it failed over to the other link, then the ping continued, did a tracert and indeed it's on the other link.

Thanks Dan and to everyone who had a time to look and share their thoughts.

Joseph W. Doherty
Hall of Fame Expert

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Posting

If your two links' bandwidth is the same, and if the delay difference isn't significant (as in it would not have an adverse impact on your traffic), you might consider just "lying" to EIGRP and make the two paths equal cost.

Regarding the issue of route-maps not automatically re-routing, I recall (?) PBR can be structured such that when the designated path is not available, another or default routing path can be used. 

@Joseph - Thanks for the reply, the route-maps are the temporary solution we did to force data traffic on the higher delay link but we wanted a simpler configuration by influencing eigrp.

We also considered to make the two path have equal cost, but we wanted to give preference on the low delay link for routing voice and data to the higher delay link but at the same time make it fail-over when either would fail.