Redundancy and Load Balancing to ISP

[nxm]

We have 2 routers (3925) connect to the ISP through individual DS3 (T3) Connection.  I want to ensure redundancy and proper load balancing.  Sample configs and recommendations would be appreciated.

[paolo bevilacqua]

Considering the size of your infrastructure and speed acces, the best solution would be BGP.

In alternative, a load-balancing appliance between firewall and routers.

In either case, I recommend you hire a reputable consultant or certified cisco partner for the job.

[Mahesh Gohil]

Hello,

Please find below inputs

> Run HSRP between swich and two routers
> Run BGP between Router and ISP. I am just briefing BGP part below

  > Let's assume you have one pool of /23. Divide it into two /24 parts

  > Prepare three prefix list

    ip prefix-list ISP-A-PRIMARY permit
    ip prefix-list ISP-B-PRIMARY permit
    ip prefix-list BACKUP permit

  > Prepare two route-map for out direction
   
    route-map ISP-A-PRIMARY permit 10
    match ip address prefix-list ISP-A-PRIMARY
   
    route-map ISP-A-PRIMARY permit 20
    match ip address prefix-list BACKUP

    set as-path prepend

     route-map ISP-B-PRIMARY permit 10
     match ip address prefix-list ISP-B-PRIMARY
   
    route-map ISP-B-PRIMARY permit 20
    match ip address prefix-list BACKUP
    set as-path prepend

  > Put this route-map in out direction with bgp peer respectively

    neighbor x.x.x.x route-map ISP-A-PRIMARY out
    neighbor y.y.y.y route-map ISP-B-PRIMARY out

Above will ensure load sharing between two ISP for incoming traffic. For out direction you can play with local-preference . It is much depends upon what

you are learning from provider end (default-route, Full BGP, Partial table)

Hope this helps

Regards

Mahesh

[Anand Mittal]

I am working in an ISP, facing a similar issue for a customer...

but the problem is the pool he's advertising is /24 one...if we divide further it will go to /25 & that is not acceptable in ISP's any suggestions???

[nihit-tandon]

Can any one update when the customer has /24 IP block.

[Mahesh Gohil]

Hi,

If customer is having /24 pool ISP will not accept in bracket of /25.

Now say If ISP agree on this then there is a way.

There are two approaches

1/ Accept /25 from customer and also ask customer to advt. /24 along with this. Advt. only /24 to upstream (from ISP) and hide /25 one. (no need to do

    anything upstream will deny that).

    So if someone on internet send traffic for first /25 it will follow /24 route and once that packet is entered the ISP network it will have two /25

    route so once will be prefered.

    Internet User------/24--------Upstream-------/24---------ISP-------First/25------CustomerA

                                                                             |

                                                                             |

                                                                   Second /25

                                                                             |

                                                                     CustomerA.

2/ Next approach is customer advt. only two /25 and ISP itself advt. /24 by putting /24 route pointing toward null0 in one of his router.

Regards

Mahesh