BGP with 4 ISP

[TuralLachinov]

Hello All,

I have Switch 6509E wich is the core of the network, and we have 4 llink form 4 ISPs, all the link will work at the same time,

could please help to configure, how can I confiugure the BGP , as I know if I configure bgp it will work with one ISP as an active link,

if that link goes down it will automatically begin to work with other ISP. My question is that how can configure the network so that,

some vlans work with one ISP, some vlans with the others and so on.

If configure it with route map I will have to track every time to change the confiration if the links goes down, but I do not want to track it, Can I do anything

with BGP to implement this task?

The core of the network is Switch 6509E, intervlan routing is implemented on it, no dynamic routing is enabled.

The firewall module installed on it the implementing the NAT processes. 

[paolo bevilacqua · Accepted solution]

Do you have your own Autonomous System Number ?

Do you have a CCIE or someone with equivalent experience and knowledge ?

If the answer to either questions is 'no', you should wait until both requisistes are fullfilled before attiming anything.

[TuralLachinov]

Hi Paola,

Yes we have already received AS nummer, only needs to begin configuration, of cource I can configure BGP, but simple variant, I need advanced configuration in order to work with 4 ISP and need to divide the vlan into 4 group somehow and assign each group an ISP so that if link goes down of any of these ISP, the vlan group assigned for this group goes to internet throug the ithe one, is it possible with BGP ?

[paolo bevilacqua]

Yes, but NAT has to be taken int consideration. Basically, you will use MED, conditional et other advanced tecniques to set your policy when adverting the prefixes then used to NAT you internal VLANs. All this explained in documenation, as well in many books and white papers.

Thanks for the nice rating and good luck!

[TuralLachinov]

Can I achive it with MED ? Will the all ISPs work actively?

But if I will show default route to the first ISP, the rest will not work active as I know, yes ?

regards

Tural

[Alessio Andreoli]

Hi Tural,

i wouldn't say you need an adavanced configuration to work with 4 ISPs. I would instead concentrate on an advanced design of the BGP portion of your network. If you do not have any particular need you can agree with at least half of these ISPs a very stable wa to connect to them. Configuration wise you will not find issues. 4 ISPs are not so many. Define the roles of the ISPs, i'd say this is the main issue, and the just write down the code your design requires.

Should you need some help (for design) just let me know.

Hope this helps

Alessio

[TuralLachinov]

Hi Alessio,

what I mean is that I do not want to track manually, I want that bgp should do it, I am looking for any

option in order to achive it.If I simply configure bgp it will work of cource, but this is not all what I want,

I want that some vlans active work with one ISP , some with the second ISP, and rest with the 3rd ISP

is it possible? if yes how?

How designing can help, please offer!

regards

Tural L

[Alessio Andreoli]

Hi Tural,

a simple solution would be to advertise the same subnets on all your BGP links taking care to implement a more specifi route on your primary link while a less specific (installed on the routing table but NOT as best-route) on the secondary link.

so for example on link 1 you will have

Vlan 1 (longer prefix), Vlan 2( longer prefix), vlan 3( less specific prefix), Vlan 4 ( less specific prefix)

while on link 2 you will have

Vlan 1 (less specific prefix), Vlan 2( less specific prefix), vlan 3( longer prefix), Vlan 4 ( longer prefix)

This combined with some prepending  should accomplish  what you are asking for.

HTH

Alessio