Load sharing

Answered Question
Jul 26th, 2009

Hi guys ,

I have 4 routers ( 2 routers per site ) ,

between these two sites ,there are total 8 E1s (4 E1s between two pairs), so I`m going to load balance traffic between these 8E1s and routers, Please take a look at attachment. I'm not able to use MPLS-TE , because routers are 2811 , also OSPF and EIGRP are not able to load balance . GLBP is not allowed in this network . Defining two gateways is not allowed with HSRP or VRRP .

I would appreciate if you can help me in this regard .

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Correct Answer by Joseph W. Doherty about 7 years 4 months ago

". . . because routers are 2811 , also OSPF and EIGRP are not able to load balance ."

Why do you believe that?

If you're thinking of equal cost only load balancing, yes, by default, having all traffic egressing via just one of the two routers would not use the other router's WAN links, but I've done it for OSPF by setting OSPF costs such that the gateway router "sees" equal costs both via it's own WAN links and through its peer. With EIGRP, you would also have the option of unequal cost load balancing.

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Marwan ALshawi Sun, 07/26/2009 - 21:37

actually define two VIPs of HSRP is allwed and possible

you can define two HSRP groups in each site

and assigne half of the PCs one VIP as default gateway and the other half they can you use the other VIP

this way half of your PCs will use first router as the active and other half will use the other router as the active (loadsharing)

for example

router1

int fa1/0

standby 1 ip 10.1.1.1

stanby 1 priority 150

standby 1 preemt

stanby 2 ip 10.1.1.10

standby 2 preempt

stanby 2 priority 80

this way this router will be active for group 1 and any PC with defualt gateway 10.1.1. will use this one as the active

wish the idea is clear

other option you can use ospf with eqault cost links and cef forwarding loadblancing

good lcuk

hope this helps

amir_taghavi Sun, 07/26/2009 - 21:56

Thanks for your replay , I meant I cannot use two deault gateways (MHSRP) , I wanna make loadbalancing for routing .

For OSPF , equal cost and CEF , how can I put OSPF cost , I can only load balance for cross routers , but it's not desired , I want to loadbalance between point-to-point routers .

Cef loadbalancing methos is per destination , If I changed to per packet may be packets are reordered .

Giuseppe Larosa Mon, 07/27/2009 - 01:48

Hello Amir,

two notes:

a) if you use PPP multilink bundle it has its own per packet load balancing algorithm and doesn't rely on CEF

b) GLBP is the only way in a scenario like yours to provide effective usage of all 8 links in both directions.

provide the customer an explanation of GLBP benefits and they should allow for its usage.

End user hosts don't care of OSPF or other routing protocols.

OSPF could come into play if L3 devices were connected to the routers but your network diagram shows PCs and L2 devices.

Hope to help

Giuseppe

amir_taghavi Mon, 07/27/2009 - 02:47

Hi Guiseppe ;

My issue is about layer3 load sharing , on layer 2 yes, ppp multilink will loadbalance between 4 E1s , Glbp also works with source IP , which means if you have 3 PCs , one router would carry more traffic than the other ,

finally , I obliged to use MPLS-TE , it's fine now traffic shared between E1s , 50% - 50% .

Correct Answer
Joseph W. Doherty Mon, 07/27/2009 - 03:16

". . . because routers are 2811 , also OSPF and EIGRP are not able to load balance ."

Why do you believe that?

If you're thinking of equal cost only load balancing, yes, by default, having all traffic egressing via just one of the two routers would not use the other router's WAN links, but I've done it for OSPF by setting OSPF costs such that the gateway router "sees" equal costs both via it's own WAN links and through its peer. With EIGRP, you would also have the option of unequal cost load balancing.

amir_taghavi Mon, 04/05/2010 - 00:19

Yes, you are right, but how about CEF, because after routing occurs, CEF will handle the traffic between the links. Basically CEF is working based on per-destination algorithm, you can change it to soure*destionation or source*destination*port, the last algorithm is the best one, but if you disable the CEF, the per packet load sharing algorithm will be used.

I just disable the CEF, because the router supports only per destination loadsharing.

Marwan ALshawi Mon, 04/05/2010 - 00:55

but keep in mind that per packet loadsharing has some drawbacks

such as

it is more CPU intensive

you may get out of sequence TCP

amir_taghavi Mon, 04/05/2010 - 00:59

Si ,, I aware of this issue. but till now nothing wrong happend, my clients are using FTP. they didn't report any issue.

mazboot..,

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