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Community Member

BGP Load sharing

Hi

Schematic has the current network details

Current Setup (ISP1 is prmary and ISP2 is secondary)

==Doing EBGP with 2 diffrent service providers.

==Both internet links terminated on 2 diffrent routers

==getting default route in BGP from Both service provider

==Default Route received in Internet router is reditributed in OSPF which is running betwene Internet router and L3 switch.Default route from ISP 1 is redistributed without any metric while default route from 2nd isp redistributed with metric so L3 switch has default route towards ISP1

==No IBGP running between both internet router

==owns pool from apnic

Future Requirement(Want to use both service providers at a time)

==want to use both links for outgoing traffic (few networks from ISP1 and few networks from ISP2)

==want to use both links for incoming traffic

what i feel is

==need to run IBGP between 2 internet routers.Only 1 default route will be active probabaly ISP1 using local preference.

==for incoming traffic,i will announce few networks with ISP1 BGP using AS prepend and  so that those networks would be preferred over ISP2 and vice versa.

==need ur confirmation on this

Question is

===Default route would be preferred over ISP1 using local preference so how i will ensure ISP 2 will also Send outgoing traffic.As i am getting only default route in BGP from both the service providers ,outgoing traffic from 2nd provider seems difficukt.please suggest.

6 REPLIES
Cisco Employee

Re: BGP Load sharing

Sameer,

I have worked on a very similar requirement where I did the below,

No iBGP between two Internet router. eBGP between Internet router and respective Service Provider and I will receive only default route from service provider.

OSPF will be enabled between two Internet router and Internal L3 switch. Both Internet router will originate default route via OSPF using "default-information originate (without "always" keyword).

I had 4 internal routes that I need to advertise to external world. I will advertise all 4 in both Internet routers (Prefix1, Prefix2, Prefix3, Prefix4), but prefix1 and prefix2 will have AS path prepended in Internet router1 and prefix3 and prefix4 will have AS path prepended in Internet router2.

By this config, you can acheive load balancing in both incoming as well in outgoing direction without compromising with redundancy.

When eBGP between Internet routers and SP are fine, the default route will be received to respective Internet router and OSPF will originate the default route. If any Internet router looses itz connection to SP, default route via eBGP will be missing from routing table and OSPF will withdraw the advertised default route.

Same happens with prefix advertising to external world.

HTH,

Nagendra

Community Member

Re: BGP Load sharing

Hi

Thanks for the reply...

couple of queires

===u r redistributing the default route from both the service providers wih default metric so L3 switch will have 2 default route for outbound traffic so it will do per packet/per destination load balancing but still i dont have control on particular network will use isp1 as primary and particular network use isp2 as primary ( i have 16 class c so still i cant send first 8 class c with isp1 and last 8 class c with isp 2 as primary )

====with as path prepend u will get the inbound traffic for those network via particular isp but i dont think it will control your outbound traffic.

====can u share your current configuration...u can replace the actual public ips with dummy private ips.

Cisco Employee

Re: BGP Load sharing

Sameer,

===u r redistributing the default route from both the service providers wih default metric so L3 switch will have 2 default route for outbound traffic so it will do per packet/per destination load balancing but still i dont have control on particular network will use isp1 as primary and particular network use isp2 as primary ( i have 16 class c so still i cant send first 8 class c with isp1 and last 8 class c with isp 2 as primary )

If your task is to route traffic based on source, (i.e) set of source should choose ISP1 and other should use ISP2 with fallback redundancy, you need Policy based routing configured. With plain routing protcols, you cannot acheive routing based on source.

====with as path prepend u will get the inbound traffic for those network via particular isp but i dont think it will control your outbound traffic.

You are right. AS-PATH prepend is to influence incoming traffic. In my initial post if you see, I have mentioned that I used OSPF to influence outgoing loadbalancing and BGP AS-PATH for incoming load balancing.

====can u share your current configuration...u can replace the actual public ips with dummy private ips.

I dont have the config handy. I can help you if you with configuration if you have finalised your design.

HTH,

Nagendra

Community Member

Re: BGP Load sharing

Hi

you have mentioned about the policy based routing in this scenario as i need outbound traffic to be sent based on Source ip subnet.can you please let me know how it will be configured.

to start i will get both teh default route in my l3 switch so that it will have 2 default route.what i understand is,the Lan interface which is connected to L3 switch will have the policy map applied which will be define the next hop.(In my case i will define next hop as either router1interface or Router2 interface connected to L3 switch).

i am little confised on how my config will look like.can you please help me on the same.

Cisco Employee

Re: BGP Load sharing

Hi,

Please find the configuration below,

1. Configure the ACL to match the source address for which you need to set the next hop as below,

access-list 1 permit

access-list 2 permit

2. Now configure the route-map to set action as below,

route-map PBR permit 10

match ip address 1

set ip next-hop

route-map PBR permit 20

match ip address 2

set ip next-hop

3. Apply the same under incoming interface of the source address,

interface g0/0

ip policy route-map PBR

In your case, Do you have any specific/strong reason that a set of source should prefer a particular ISP?. If not, It is recommended to leave the decision to be taken by L3 switch itself.

HTH,

Nagendra

Silver

Re: BGP Load sharing

I would recommend GLBP as an option for your set-up.

This link is for the 6500, but the scenerio is still the same.

http://www.cisco.com/en/US/products/hw/switches/ps708/products_configuration_example09186a00807d2520.shtml

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