Help needed for configuring BGP Multihoming

[neonjacob1234567890]

Hi,

I need to configure BGP multihoming with two ISP using only one Router(L3 Switch with BGP). We have our own AS Number and a /24 IP Pool. We need to configure it as normal failover, we don't want to load balance between the two ISP links. We need ISP A to be the primary link through which all (IN & OUT) the traffics would pass through normally, and the ISP B  link would be used only if ISP A link fails.

ISP A should start handling the traffic again, as soon as the ISP A link becomes active.

Here is a Diagram of the Scenario :

Please help

[paul driver]

Hello

Please review this below example:

The filter list 10 is to prevent your site becoming a transit path between either ISP

I have utilised the bgp weight attribute for preferred egress traffic and As-prepending for preferred ingress traffic

ip as-path access-list 10 permit ^$

route-map AS-Prpend permit 10
set as-path prepend 999 999 99

router bgp 999
neighbor x.x.x.x remote-as <ISP1>
neighbor x.x.x.x weight 40000
neighbor xx.x.x filter-list 10 out

 neighbor y.y.y.y remote-as <ISP21>
 neighbor y.y.y.y  weight 30000
 neighbor y.y.y.y filter-list 10 out
 neighbor y.y.y.y route-map AS-Prpend out

res

Paul

[neonjacob1234567890]

Dear paul,

Thank you for the quick reply. I'll try it out and revert back asap.

Regards

[paul driver]

Hello

Forgot to mention please ammend that example to fit your ASN numbering and peering addressing

res

Paul

[neonjacob1234567890]

Hi paul,

Is the configuration sufficient or do i need to perform any other additional configuration?

Do i need to configure "ip prefix-list"

Regards

[paul driver]

Hello

i have not see your existing configuration so cannot really comment- the example I gave would give you the prefer path and backup path to either ISP but  as far as any specific requirements that you already have I cannot say

The prefix command related to the bgp regular expression so to advertise only local routes to either ISP and to prohibit you site from becoming a transit path for either iISP.

res

paul

[neonjacob1234567890]

Hi paul,

Here (attached) is the current config. Please take a look and help.

Regards

[paul driver]

Hello

What i can establish is your excepting a deault route from a ISP and advertising one specific network

What i dont see is dual isp peering like what your topology diagram is showing So i guess this 2nd ISP is a forthcoming implementation?

res

Paul

[neonjacob1234567890]

Hello,

Yes, its forthcoming, only ISPA part is configured till now.

Thanks

[paul driver]

Hello
Please review the following example - 

router bgp 999
neighbor Stan peer-group
neighbor Stan password xxx
neighbor x.x.x.x peer-group
neighbor y.y.y.y peer-group
neighbor x.x.x.x remote-as <ISP1>
neighbor x.x.x.x description ISP1
neighbor y.y.y.y remote-as <ISP2>
neighbor y.y.y.y description ISP2
maximum-paths 2

 address-family ipv4
 neighbor Stan route-map ISP-IN in
 neighbor Stan filter-list 10 out
 neighbor x.x.x.x activate
 neighbor x.x.x.x weight 40000
 neighbor y.y.y.y activate
 neighbor y.y.y.y weight 30000
 neighbor y.y.y.y route-map AS-Prpend out
 maximum-paths 2
 no auto-summary
 no synchronization
 network 1.1.1.0 mask 255.255.255.0
 exit-address-family



ip as-path access-list 10 permit ^$    <----- Advertised ONLY local routes

route-map AS-Prpend  <-- Prepend all local routes with local ASN to least prefferd ISP
set as-path prepend 999 999 999

ip prefix-list ISP1-IN permit 0.0.0.0/0  
route-map ISP-IN permit 10 <-----------Allow only a  received Default from both ISP's
match ip address prefix-list ISP1-IN

res
Paul

[neonjacob1234567890]

Thanks paul,

I'l test this over GNS3 asap.

Regards

[paul driver]

Hello

Please note the changes I have made are regards adding Peer-groups and your exsitng outbound route-map -

res
Paul

[neonjacob1234567890]

Hi paul,

Can you please tell what are these lines for?

================================

neighbor Stan peer-group
neighbor Stan password xxx

 neighbor Stan route-map ISP-IN in
 neighbor Stan filter-list 10 out

================================

I couldn't understand them.

Regards

[paul driver]

Hello

Yes of course - neighbor xxx peer-group  - This is a peer group,its 3 of bgps different kinds of peer templates - ( this the basic one) -Which allows you share the same polices to multiple peers

In the configuration I supplied both your ISP peering will SHARE 3 polices -

password ( optional) - simple peering security between peers
filter-list 10   <---------- to negate transit traffci from ISP's
route-map ISP-IN in  <-------------- this is your exsitng route-map uou had to allow default route from the ISP

FYI -  The other 2 peering group templates you can uiltlze are
Peer Session
Peer Policy

But I didnt wont to convolute the posting with such configuration---

I hope this help - any other queires please dont hestitate is ask.

res
Paul

[neonjacob1234567890]

Hi,paul

While configuring the line:

neighbor y.y.y.y route-map AS-Prpend out

I get an error: % Invalid command for a peer-group member

I've attached current configuration for your reference.

Thanks for the help