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Community Member

BGP Loadsharing Setup

Hi All,

I've seen a number of examples of this setup where 2 blocks are being advertised from the customer site(s) and some form of load sharing is achieved. Say I am advertising a /24 block to the internet from my site. I have 2 /30 point-to-point connections ( Router 6509 A goes to ISP 1 and Router B 6509 goes to ISP 2). I will have eBGP peering sessions set up with the ISP's and iBGP peering between my own two routers.I am also using GLBP for gateway redundancy between my two routers. Can someone tell me what is the best setup to consider using if I want to achieve inbound/outbound loadsharing on these connections.Also what is there to consider in this scenario and what do i need to be aware of from a provider perspective etc. ?

Thanks in advance,


Hall of Fame Super Silver

Re: BGP Loadsharing Setup

Hello Frank,

if you have only one /24 public address block you will be able to achieve outbound load balancing (to the internet) but not in the inbound direction.

if you had two /24 IP subnets you could try to influence return path with selective AS path prepending.

you would need a private agreement between you and the two ISPs in order to have them accept /25 prefixes and to route them between them the two providers.

being  the two ISP links over two different routers you don't need the hidden command

bgp bestpath as-path multipath-relax

GLBP will be effective if client vlans are directly connected to border routers otherwise if there is a firewall it will behave like HSRP

Hope to help


Community Member

Re: BGP Loadsharing Setup

Thanks a lot Giuseppe.


On Tue, Mar 16, 2010 at 2:19 PM, giuslar

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