BGP Load Balancing

[retsek1984]

Hi,

I have 3 ISP's and I am advertising my IP blocks to all of them. I would like to find out how I can influence outbound traffic to go out the same way its coming back in i.e If I have 192.168.1.0/24 being advertised to ISP X , I would like it to go out thru ISP X...

[Bryan Lee]

Hi Kester,

Do you have your own AS? is it routed with your all other ISPs?

[retsek1984]

Hi Anil,

I have my own AS number..and it is indeed routed on all ISP's

[sansarav720e]

Hi Kester ,

                If you want to influence outgoing traffic via particular ISP .X this change can be achieved only via Static route with high weightage to rest of two ISP Y,X .

                Else if you dont want static route you can have weightage attributes configured towards your neigbor ISP.X ,Y,Z ,which will have influence to your outgoing traffic

router bgp 65300

network 192.168.1.0 mask 255.255.255.0
neighbor 10.10.10.1 remote-as 65311
neighbor 10.10.10.1 weight 100
neighbor 10.20.20.1 remote-as 65312
neighbor 20.20.20.1 weight 200

neighbor 10.30.20.1 remote-as 65313
neighbor 20.20.20.1 weight 300
no auto-summary

HTH

San

[retsek1984]

Hi SANTHOSHKUMAR,

Thank you for the response. However my idea was if I have the following setup

My IP Blocks 192.168.1.0 being advertised to ISP X

192.168.2.0 being advertised to ISP Y

192.168.3.0 being advertised to ISP Z

For outbound traffic I would like a setup in which

192.168.1.0 goes out and comes back through ISP X

192.168.2.0 goes out and comes back through ISP Y

192.168.3.0 goes out and comes back through ISP Z

Idea I am trying to configure is a block being advertised to a particular ISP should be the same it goes out as explained above.

Regards,

[sansarav720e]

Hi kester ,

             yeah this can be achieved by using route-map on your interface configuration

ip access-list extended ISP1

permit   ip 192.168.10.0 0.0.0.255 any

ip access-list extended ISP2

permit   ip 192.168.20.0 0.0.0.255 any

ip access-list extended ISP3

permit   ip 192.168.30.0 0.0.0.255 any

route-map traffic permit 10
match ip address ISP1
set ip next-hop x.x.x.x
!
route-map traffic permit 20

match ip address ISP2

set ip next-hop y.y.y.y

route-map traffic permit 30

match ip address ISP3

set ip next-hop Z.Z.Z.Z

If your router interface carries these all 3 network traffic on fastethernet 0/1

interface fastethernet 0/1

ip policy route-map traffic

else if you each network segment defined on separete physical interface on router

ip access-list extended ISP1

permit   ip 192.168.10.0 0.0.0.255 any

ip access-list extended ISP2

permit   ip 192.168.20.0 0.0.0.255 any

ip access-list extended ISP3

permit   ip 192.168.30.0 0.0.0.255 any

route-map traffic1 permit 10
match ip address ISP1
set ip next-hop x.x.x.x
!
route-map traffic2 permit 10

match ip address ISP2

set ip next-hop y.y.y.y

route-map traffic3 permit 10

match ip address ISP3

set ip next-hop Z.Z.Z.Z

interface fastethernet 0/1

ip policy route-map traffic1

interface fastethernet 0/2

ip policy route-map traffic2

interface fastethernet 0/3

ip policy route-map traffic3

[Andy Roberts]

Influencing inbound traffic from the Internet is never simple. I have a similar setup and we are using AS path prepending with some degree of success, For example advertise 192.168.1.0 to ISP A and prepend to ISP Y and Z then 192.168.2.0 to ISP Y and prepend to ISP X and Z etc. Not perfect as you may find your prepends stripped out at some point downstream but we certainly saw a reduction in asymmetric routes.

Regards

Andy.

Sent from Cisco Technical Support iPhone App

[Rahul Kukreja]

Yes, you can use AS Path Prepending to influence the inbound traffic.

By Advertising

Subnet 1 to ISPA without modifying the AS Attribute.

Subnet 2 and 3 to ISPA with prepending the AS.

In that manner if the destination has 3 paths to choose the best from ; then it will choose the path with the smallest AS Path by default. ( which would be ISPA for Subnet 1.)

But before implementing this, please let me know is there any other site were you are using the same AS Number.

And advertising this routes to that site via BGP.

If that is the case then all routes would be rejected... as we have same AS Number for the 2 sites...