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AToM / EoMPLS Load Balancing

I am running VLAN Based EoMPLS from 7609_A to 7609_F in the following configuration. The ingress and egress ports are the Gig Ethernet LAN ports on a 2GE+4GE-WAN OSM card. Each 7609 has a Sup720 with PFC3BXL running 12.2(17d)SXB6 whilst GSRs are running 12.0(26)S5a

CE_1---7609_A---7609_B===GSR_C---GSR_D===7609_E---7609_F---CE_2

Where '===' is two links and '---' is a single link.

I've had a good look through the forum and other documentation but can't seem to find anything that answers my questions.

1) Is there any way to load balance on a granular level (eg. per packet basis) on the multiple links between 7609s and GSRs. It seems that there is some load balancing but only on a Virtual Circuit by Virtual Circuit basis over the multiple links eg. If I setup one or more Virutal Circuits from 7609_A to 7609_F to provide a link between CE_1 and CE_2, VC1 goes down link 1, VC2 goes down link 2, etc. according to some hashing algorithm. This is not very helpful because at times, there is only one VC and as an individual VC approaches the link bandwidth of one of the multiple links, other traffic load balancing across the multiple links evenly causing an imbalance and potential oversubscription of one of the links.

CEF shows 2 equal cost paths across the multiple links to the remote 7609. The routing table also shows 2 equal cost paths to the loopback of the remote 7609. MPLS has the same label for both equal cost paths to the remote 7609.

According to documents I have read on AToM (EoMPLS), MPLS should be able to load balance within the core MPLS network. What configuration needs to be done to achieve this? Or can't it be done?

2 REPLIES
Cisco Employee

Re: AToM / EoMPLS Load Balancing

In an EoMPLS scenario, the load-labancing is indeed done based on the inner label (VC label). So load balancing will not happen with one VC label.

If you have only one active VC in your network, what difference does it make to load-balance or not?

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
New Member

Re: AToM / EoMPLS Load Balancing

Hi, any hint on these one? I have the same case but with multiple AToMs each one with its own VC. Many VCs are beggining from various routers and terminate into some other routers. I have seen that ios probably cef cannot do proper load balance, although i adjusted the cef algorithm universal it seems that it is fixed but if there is a failure in the network the load balance gets worst. I know that in order to make the load balance is to look in the inner label but it seems cef does it stuff and i dont know if it works well...so in general can it be done a proper load balance in an mpls environment? How about layer 3 vpns what is the criteria of doing load balance?

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