Bgp Planning

[burak-isiksoy]

Hi,

We are planning to use BGP with the following topology. But we have some hesitations

I  would likte to hear about your opinions about the case. Is it preferable to use Bgp wih such configuration what would be the possible drawbacks.

Also in case I change something on bgp configuration (As path etc. )how long it takes to see the affects of updates.

I am planning to advertise /25 subnets of a /24 network from 2 sites.

First half of the network should be reachable from site 1 and the second half of the network from site 2.

In case of problem lets say site 1 unreachable  I want to be able to reach both subnets from 2nd site and vice versa.

As outgoing traffic I want to use R1 on both sites as prefered uplink.Also I am planning to load balance the outgoing traffic between ISPs.

BR.

Burak

[Marwan ALshawi · Accepted solution]

well BGP is this way you go as BGP considered and exterior routing protocol and it has more capabiites to give better control over the routers and path selection

based on what you described above you can advertise first /25 via site1/R1 using better AS path and advertise the same /25 from R2/site2 using higher AS path for the same /25

you can use the same concept for the other /25 this is for inbound direction from the ISP to your sites

however for the outbound this is something you need to design and aligne with the inbound for better route selection and to avoid asymmetrical routing

so if you need R1/site1 to be the preferred outbound direction and you use BGP/iBGP internally then you can increase the local preference of the routes coming from site1/R1 to be preferred by internal ibgp network

BGP can do load sharing per destination as other routing protocols dose

but if you are peering with differnt ISPs/AS numbers then you need to enable a hidden command in BGP to do so

https://supportforums.cisco.com/message/765846#765846

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00800945bf.shtml

hope this help

[Marwan ALshawi · Accepted solution]

let us know if you need any further assistance !

[burak-isiksoy]

Hi,

Thanks for the help. I also check with the ISP and they also confirmed. So i will go according to original plan.

[Marwan ALshawi]

happy to help and thanks for the nice rating

[arpan Sarkar · Accepted solution]

For a better convergence you may use bgp scan time and advertisement interval. And yes it will work from the enterprise viewpoint but load balancing towards ISP would only work if each and every attributes remains same for a particular prefix....hope it may help.

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