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Loadsharing for dual ISP

vicky.dhas
Level 1
Level 1

Friends,

I have taken MPLS from 2 ISPs and they are configured in active-back up using HSRP in LAN.Now i want to loadshare traffic between both ISPs to optimize my avaialbe resource.can you suggest best method to achieve that for forward and reverse traffic.

regards

Vicky

8 Replies 8

rsimoni
Cisco Employee
Cisco Employee

Hi Vicky,

with dual-home ISP's there is no way to achieve load balancing as BGP selects only the single best path to a destination among the BGP paths that are learned from different AS's.

What you can achieve is some degree of load sharing (which is not load balancing though) from your L3 switch perspective (which is the only router in your topology which has multiple paths towards the same destination). Provided that all your hosts in both sites use the local L3 switch as default gateway you might redistribute the routes coming from the 2 ISPs into OSPF (as external routes) making sure that the cost to reach TATA and Airtel CEs is equal (from L3 switch perspective). This way you will have equal cost sharing for the same remote prefixes on the L3 Switch.

However this way is not determistic and potentially risky as you might have asymetrical routing (i.e. host in Bangalore uses TATA to reach Plants host but replies travel through Airtel). Some applications might have issues with that and FWs could drops those flows.

Read this article which throws some ideas on how to achieve similar results:

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00800945bf.shtml

regards,

Riccardo

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Posting

with dual-home ISP's there is no way to achieve load balancing as BGP selects only the single best path to a destination among the BGP paths that are learned from different AS's.

Actually this can be done, and I've done it, see: https://supportforums.cisco.com/message/3864948#3864948

Joseph W. Doherty
Hall of Fame
Hall of Fame

Disclaimer

The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.

Posting

On the LAN side, changing from HSRP to GLBP might work for you.

On the WAN side, using OER/PfR might be the "best" for optimal dynamic load sharing and end-to-end performance.  Static load sharing, via a routing protocol's multi-path, might be possible too.

well, anything is possible, but considering the type of question asked by Vicky and the attached topology I don't think that PfR is a realistic solution in this case due to the considerable efforts required in term of hardware and software requirements and the completely new subset of networking knowlegde and skills (which is not straightforward nor intuitive...).

Using a metaphor nuclear power is an excellent way to warm up water, but I am not sure it is a wise idea to suggest building a nuclear plant in your back garden to have hot water for your shower....

Riccardo

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

well, anything is possible, but considering the type of question asked by Vicky and the attached topology I don't think that PfR is a realistic solution in this case due to the considerable efforts required in term of hardware and software requirements and the completely new subset of networking knowlegde and skills (which is not straightforward nor intuitive...).

OeR/PfR might be something a little more solid than "anything is possible".  It's also realistic as I've run OER/PfR on 2811s working with dual MPLS (L3 VPN) vendors.  I didn't find hardware and software requirements much of an impediment.

"type of question"  Well a question included "can you suggest best method to achieve that for forward and reverse traffic."  IMO, working with just Cisco routers, it doesn't get much better.

Does it require new knowledge and skills?  Indeed it may.  I don't see Vicky's questions discounting a possible solution if new knowledge and/or skills would be needed.  I didn't find a basic OER/PfR load sharing configuration that complex.

"not straightforward nor intuitive" - ah, touche  - you've read Cisco's OER/PfR documentation? - laugh.

Using a metaphor nuclear power is an excellent way to warm up water, but I am not sure it is a wise idea to suggest building a nuclear plant in your back garden to have hot water for your shower....

I'm not quite sure OER/PfR is as complex as building your own backyard nuclear power plant to warm up water for you shower; maybe a better metaphor would be a solar water heater .

Anyway, to recap, and given what the OP's diagram seems to show.

GLBP might be the "easiest" solution.

Multipath routing would be more complex and might (statically) balance flows better.  What Riccardo was suggesting, using the L3 switch(es?) as gateway would simplify multipath routing, but it might also be done from a gateway router (i.e. either via EIGRP's variance, or "fibbing" to other routing protocols that only support ECMP [I've done the latter pre GLBP and OER technologies]).

OER/PfR can do dynamic load balancing and analyze (and tune) for performance.  It can be used alone, but personally, I like to start with GLBP or routing multipath and then allow OER/PfR to optimize/tune.

Thanks Joseph,Riccardo

Can GLBP can balance reverse traffic too?

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

Liability Disclaimer

In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.

Posting

Vicky Dhas wrote:

Thanks Joseph,Riccardo

Can GLBP can balance reverse traffic too?

No, but if you use GLBP on the other side, the other side's balanced egress becomes near side balanced ingress.

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