BGP Loadbalancing and traffic shaping.

[rodney.chatman]

I have two ISP connections that I'd like to configure failover and loadbalancing between.  Here is what I'm hoping to accomplish:

Example:

I have six IP address blocks.

1.1.1.1/24

2.2.2.2/24

3.3.3.3/24

4.4.4.4/24

5.5.5.5/24

6.6.6.6/24

I would like all 6 blocks to be advertised via both ISP's for failover purposes.  I would like for the first 3 /24 blocks to ingress via ISP A and the last 3 /24 blocks to ingress via ISP B.  Should either ISP A fail, however the first 3 /24 blocks will failover and ingress via ISP A.

AS Prepending would be my prefered method.  For my advertisements to ISP A prepend 3 AS paths to the last 3 /24 blocks and for my advertisements to ISP B prepend 3 AS paths to the first 3 /24 blocks.  Unless of course there is a better best practice to accomplish this.

[daniel.dib]

Look into if your ISP supports communities. By adding communities you can tell the ISP to prepend for you and to do certain traffic engineering like to set a lower local preference within the ISP network.

The second best method would be to use MED or prepending.

Note that you can never force someone to select a certain path in BGP unless you don't advertise the secondary path until the primary goes down.

Do you need to have symmetrical paths? That could be a concern for your setup. Look into conditional BGP as well.

Daniel Dib
CCIE #37149

[rodney.chatman]

The paths will be symmetrical as we'll be using route-maps to to set next-hop based on source IP address.  What I'd really like to know is if it's possible to advertise all 6 IP blocks but half with as-prepetion and half without to each ISP?

Would the following configuration accomplish this task:

#########

# ISP A #

#########

!

ip access-list extended bgp

permit ip any any

!        

ip prefix-list prepend seq 1 permit 4.4.4.0/24

ip prefix-list prepend seq 2 permit 5.5.5.0/24

ip prefix-list prepend seq 3 permit 6.6.6.0/24

ip prefix-list prepend seq 100 deny 0.0.0.0/0

!

route-map bgp_out permit 10

match ip address bgp

route-map bgp_out permit 20

match ip address prefix-list prepend

set community 4522:4403

!

router bgp 12345

network 1.1.1.0 mask 255.255.255.0

network 2.2.2.0 mask 255.255.255.0

network 3.3.3.0 mask 255.255.255.0

network 4.4.4.0 mask 255.255.255.0

network 5.5.5.0 mast 255.255.255.0

network 6.6.6.0 mask 255.255.255.0

neighbor 8.8.8.8 remote-as 4522

neighbor 8.8.8.8 send-community

neighbor 8.8.8.8 route-map bgp_out out

!

#########

# ISP B #

#########

!

ip access-list extended bgp

permit ip any any

!        

ip prefix-list prepend seq 1 permit 1.1.1.0/24

ip prefix-list prepend seq 2 permit 2.2.2.0/24

ip prefix-list prepend seq 3 permit 3.3.3.0/24

ip prefix-list prepend seq 100 deny 0.0.0.0/0

!

route-map bgp_out permit 10

match ip address bgp

route-map bgp_out permit 20

match ip address prefix-list prepend

set community 2245:4403

!

router bgp 12345

network 1.1.1.0 mask 255.255.255.0

network 2.2.2.0 mask 255.255.255.0

network 3.3.3.0 mask 255.255.255.0

network 4.4.4.0 mask 255.255.255.0

network 5.5.5.0 mast 255.255.255.0

network 6.6.6.0 mask 255.255.255.0

neighbor 9.9.9.9 remote-as 2245

neighbor 9.9.9.9 send-community

neighbor 9.9.9.9 route-map bgp_out out

!