Load balancing between two routers

chaitu_kranthi · ‎03-10-2009

Our network is setup as such:

ROUTER A------> 4Mbps

ROUTER B------> 4Mbps

We are currently running BGP between the routers. both these routers are connected to l3 switches and are in same lan.

Please find the attached network diagram.

now my requirement is Router A has to allow all other region traffic, and router B has to allow only china region traffic.

can some body pls give me the solution.

Yasir Ashfaque · ‎03-11-2009

setup a route-map, match china prefixes and advertise default route to Router-B and for all other prefix advertise default route to Router-A

Giuseppe Larosa · ‎03-11-2009

Hello Chaitu,

RA and RB are the exit points towards other locations and they speak BGP to each other.

What is the routing protocol you use between RA and RB and the l3 switches ?

as already suggested you need to make RA more attractive for traffic destined to ip prefixes belonging to other regions and RB preferred for China region prefixes:

if you use iBGP between RA, RB and the l3 switches you need to use the local preference BGP attribute:

default value is 100 and the higher value is preferred

you can set the local preference on RA and Rb

RA:

let's suppose net 10.10.0.0/16 10.11.0.0/16 represent the other regions prefixes

access-list 11 permit 10.10.0.0 0.0.255.255

access-list 11 permit 10.11.0.0 0.0.255.255

route-map rise_locpref permit 10

match ip address 11

set local-preference 200

route-map rise_locpref permit 20

! empty block to allow other prefixes unchanged

router bgp 100

neighbor l3switch-ipaddr route-map rise_locpref out

for RB

let's suppose 10.20.0.0/16 is china region

access-list 12 permit 10.20.0.0 0.0.255.255

route-map rise_locpref permit 10

match ip address 12

set local-preference 200

route-map rise_locpref permit 20

! empty block to allow other prefixes unchanged

router bgp 100

neighbor l3switch-ipaddr route-map rise_locpref out

this should work if l3 switches with direct iBGP sessions are more then one you need to apply the same route-map outbound to all them

Hope to help

Giuseppe

Yasir Ashfaque · ‎03-11-2009

that was so kind of you Giuseppe :)

chaitu_kranthi · ‎03-12-2009

Hi,

Thanks for your quick response,

in between l3 switches and routers we are using EIGRP, and all the local subnets will be redistributed to BGP.

is the steps that you explained will work in eigrp scenario also?

second doubt was: if any one of link fails does the active router take the routes of failed routers ?

Giuseppe Larosa · ‎03-12-2009

Hello Chaitu,

>> in between l3 switches and routers we are using EIGRP, and all the local subnets will be redistributed to BGP

>> is the steps that you explained will work in eigrp scenario also

Unfortunately, it doesn't.

A different configuration is needed.

Actually you can keep the BGP config of first post but you need to add what follows

different approaches are possible here:

let's suppose both routers send an EIGRP default route to layer3 switches.

traffic can be sent by l3 switches directly to the right router if:

every router redistributes in EIGRP only the specific routes that are preferred on it if they are received by the expected BGP next hop

access-list 11 permit 10.10.0.0 0.0.255.255

access-list 11 permit 10.11.0.0 0.0.255.255

! to check BGP next hop, example

access-list 77 permit host 192.168.2.1

you need to create a new route map to be used for redistribution into EIGRP

route-map bgp-into-eigrp permit 10

match ip address 11

match ip next-hop 77

router eigrp 100

! you need to set a default-metric

default-metric 10000 1000 255 1 1500

redistribute bgp 100

on the other router you need to redistribute the routes of the china region and only if they arrive from the right eBGP neighbor

this check answers to your last question

other variations are possible:

you can use a second block to advertise china region routes with an higher metric from R1 and the other routes from R2.

or you can use a dedicated link between the two routers to run iBGP over it and let to them the duty to decide the right exit point sending only default route in EIGRP

I prefer the first solution with route details injected in EIGRP.

Hope to help

Giuseppe