BGP Traffic Managment

[alshamlan]

Dear,

Currently, we have one ISP-1 and we are planning to have another ISP-2 ( see diagram): I have a couple of qustion and senario regarding the traffic managment for BGP:

1- If the default route form ISP-1 and full BGP table from ISP-2.

- I put local preference on ISP-1 ( default route), I think the traffic will route to ISP-2 in this case since there will have least match to distinaiton. Is this right?

2- If I received the full BGP table from two ISPs:

- what I should do manage the traffic in case I shift 25% on ISP-1 and 75% on ISP-2.

- Let assume I have advertise all my subnets on ISP-1 and ISP-2 for redudncy. and I prepend some of them on ISP-1 and other on ISP-2, in this case the inbound traffic will be manged according to the traffic from each networks. But how I will mange the outbound traffic?

- If in case I face an issue with some route to certain destination that has higher latency through ISP-1, How I can change the route for the network that is advertised without prepend on ISP-1, Is in this case I have to shift this network to the other ISP? or there is another way to do it. Morever, If I shift it to ISP2 then traffic managment will changed.

3- If both ISP sending the default Route:

- Managing the traffic of inbound will be by prepend to the networks subnets, I will advertise all my subnets to both ISP for redudncy and I will prepend for traffic managment. But how we will manage the outbound traffic from each networks and how we will do redududncy.

Our Objective from having two ISPs are:

- Reduduncy.

- Higher the route performance as some ISP has better latency to certain destination and other has better to other destination.

- Traffic sharing based on the ISP bandwidth cost and type of our customers.

[Calin C.]

1 - Correct. The local-preference make sense when you have two equal cost paths to the same destination and you want to prefer one of them. Makes no sense when you have more specific prefix route vs default route. It's comparing apples with pears

2 - You have a dual-home BGP on one router, so based on the BGP behavior the installed route in the routing table will be the best path to the destination. As example, if ISP1 has better peerings, the prefixes from them will have shorter AS-path so automatically the path through ISP1 will be preferred.

To do the 25% ISP1 and 75% ISP2 will not be easy as you need to check all prefixes path, take some prefixes as desination and modify the BGP parameters in such way that you will force the path through ISP1. This is not an easy task.

Even if you prepend the AS for some prefixes, how would you know when it's enough? You will just try and guess?

I would suggest to see how the connection behave without any change, by default BGP will do its best to provide the best path to a destination. If you start messing around with BGP parameters, without knowing what is the default behavior, you may end in more problems than you try to solve.

3 -

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00800945bf.shtml#conf4

This link can provide some examples, not only for point 3.

Regarding your objectives, the BGP itself cannot achieve what you want, especially the third line with traffic sharing. Of course you can implement a complex EEM based on some IP SLA and when parameters changes (like latency) the EEM to modify the behavior of BGP, but that's picky topic and it may not function properly.

I'm also searching for methods to achieve what you want in an enterprise environment, but only with BGP is not possible.

Cheers,

Calin

3 -

[alshamlan]

Thanks Calin,

we are a small ISP not and enterprise. What is the pracitical model for ISP regarding Traffic Engineering of BGP in case there are multipule uplinks?

[Calin C.]

Unfortunately, I cannot give you a straighforward answer like "do it like this" as things are different from ISP to ISP.

However, I can point you to read some documents and learn how others are doing:

http://www.nanog.org/resources/tutorials/

- search for Tutorial: Multihoming / Traffic engineering and Tutorial: BGP technique for Service Provider

http://www.blogg.ch/uploads/BGP-traffic-engineering-considerations.pdf

- real tech stuff starts around page 16

Of course there are a lot of other resources, but I found these ones to be easy to read and ready to implement.

Cheers,

Calin

Tutorial: Multihoming / Traffic Engineering

Tutorial: Multihoming / Traffic Engineering

Tutorial: Multihoming / Traffic Engineering