BGP with two links to one ISP

[smailmilak]

Hello guys,

we have two STM16 links to one ISP. The plan is to move from the Alcatel to the new Cisco router.

There are two static routes to the BGP neighbor with one BGP session. I am not sure how we should proceed on

the Cisco router. I have never seen a BGP setup with two static routes on any Cisco BGP implementation.

Should we use two static routes to one BGP neighbor or two BGP sessions to two BGP neighbors (different IP addresses)?

Is it better in this case to have a peering with the directly connected IP address or a loopback on the ISP side?

[Marwan ALshawi]

Hi there

The static route will eliminate the main purpose of dynamic routing

As you will have two ISP links terminating in the same router it is to relay on bgp learned route rather than using static route also if will be receiving same networks over both links then you can achieve redundancy

See the bellow example of you can configure it

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00800945bf.shtml#conf2

Hope this help

If helpful rate

[smailmilak]

I was more thinking about this scenario which I found on your link

"Load sharing with the Loopback Address as a BGP neighbor"

because on the ISP side is probably the same router, not two.

But in the document they are using EIGRP in order to establish the BGP session and I am not sure if this would be possible with our provider.

[Marwan ALshawi]

No need to any igp between your end and the ISP as the link will be point to point

You need igp like eigrp if you are spanning multiple hops or peering using loopback interfaces

Which is nit the case with ISPs

HTH

If helpful rate

[smailmilak]

Yes the problem is that the ISP will probably not agree to use an IGP.

Is it then a good idea to peer with the directly connected IP addresses? Every design is using the loopback interface.

[Marwan ALshawi]

As I mentioned you do not need to use igp or peering with loopback just use the directly connected interface/ ip

[smailmilak]

So this means that I don't have any advantage by peering with loopback interfaces on ISP side over peering with directly connected IPs?

[Marwan ALshawi]

No

The peering with loopback is useful if you have to links that can reach same loopback over multiple physical links over igp this mostly used in iBGP no ebgp your case is ebgp

HTH

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[smailmilak]

Ok great, I gonna check this first and mark as correctly answered.

Thank you very much

[Arber_123]

Hello,

I am thinking of a static route alternative to achieve the result. The customer and the provider can create a loopback interface whic will be used for BGP peering (remember to add ebgp-multihop) . To reach those loopbacks you can add two static routes one per link. So the BGP routes on the customer will have the next-hop the ISP loopback address. The load sharing then will be performed by the CEF as it is configured per-packet or per destination.

Please note that BGP is not required in this case, you have a pair of link to a single ISP, i think there is no need to have all that detailed information if you are peering to a single ISP. A default static route to the ISP loopback can also be used. Also the ISP has to add a static route that contains all your ranges (a piece of cake if they can be summarized). That static route need to use the next hop of the customer loopback.

It would be glad if you share other info about this discussion.

Regards,

Arber.

[smailmilak]

If the two static routes to the ISP loopback interfaces would work and equally shared then this would be great.

You said "To reach those loopbacks you can add two static routes one per link". Why multiple loopbacks and two static routes per link? I need only one peer address in order to establish the session, which means two static routes to one IP address, one on each link.

BGP is needed because there will be another uplinks soon.

I could bundle these two interfaces, but only if the ISP supports that too. But for this is not an option.

[Arber_123]

maybe you misunderstood my proposal, there is needed one loopback IP, one on the ISP side and one on customer side.

let's say ISP: 1.1.1.1 Customer: 2.2.2.2

add two static routes

(Customer side)

ip route 1.1.1.1 255.255.255.255

ip route 1.1.1.1 255.255.255.255

ISP side

ip route 2.2.2.2 255.255.255.255

ip route 2.2.2.2 255.255.255.255

Then the traffic between these loopback will be load shared on both physical links, based as i said before as configured in CEF.

Next you peer with BGP using the loopbacks (remember the update-source, ebgp-multihop configuration).

You have a single BGP session but that is redundant on two separate links.

The BGP prefixes will use the loopback as the next-hop address, and the router will load share the traffic that is directed to that loopback.

Sorry for my english, i hope you can understand what i have written.

Regards,

Arber.

[smailmilak]

Great, it was just a misunderstanding because you added a "s" in loopback.

I will check this with my workmates and update the discussion. It will take some time...

[Mukund M Deshpande]

Hi guys ,

I have a query here , I want to configure complete redundant links as there is a higher cost on loadbalancing setup from ISP .Please let me know how  can I achive the complete redundancy between two links towards same ISP and same AS number .

Thanks 4 your reply !

-------------------------

[Marwan ALshawi]

Redundancy in active standby you can do it when youbhave two links and two bgp peers

Prepend more BGP AS numbers in the outbound direction to the ISP that to be used as bakckup one

This from the inbound traffic point of view

To effect the outbound traffic from your network out you can use local preference from the prefered ISP using inbound route map

Or as long as you have one router you can use this command towed the prefered ISP peer

Neighbor x.x.x.x weight 200

Hope this help

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