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BT Global Services: BGP FAQ

1. Why do I need BGP?

You need to run BGP on your router if you connect, or plan to connect, to multiple service providers. Although it is possible to connect to multiple service providers without using BGP, you may be confronted with routing and performance problems which can only be solved by migrating to BGP.

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2. How do I set up BGP to work with the BT Global Services network?

Once you have requested a BGP connection through your account manager, there are certain things you need to have in order for your BGP connection to function properly. If these are not done, some or all your advertisements will be filtered out by the BT Global Services network and will not be further advertised to the Internet.

The as-set object

If you plan to advertise other AS'es routes (for instance, if you have customers who also use BGP) you will need to create an as-set object in a routing registry. An as-set object is simply a representation of several AS'es, and is textual. Here's an example: 
as-set: AS-BT-ES
descr: BT Global Services Spain customers
members: AS5400, AS21368, AS-BTTEL
tech-c: CIA1-RIPE
admin-c: CIA1-RIPE
notify: notify@eu.bt.net
mnt-by: CIP-MNT
changed: c.de.loos@eu.bt.net 20020702
source: RIPE
The 'members' line contains the AS numbers you plan to advertise to BT Global Services, including your own.
Note: an as-set object may contain other as-set objects.

The route object

For each network you plan to advertise to BT Global Services, you need to register a route object in a routing registry. Here's an example of a route object: 
route: 212.58.64.0/19
descr: circular Informationssysteme GmbH
origin: AS15518
notify: guardian@circular.net
notify: netmaster@circular.net
mnt-by: CIRCULAR-NOC
changed: guardian@circular.net 20020918
source: RIPE
Note: the route object must match your BGP advertisement exactly. That is, if you plan to advertise several /24 networks individually, you need to register a route object for each of them. Registering a single route object for a bigger block containing the /24's will not function. If you need further information regarding RIPE database objects, please refer to http://www.ripe.net/ripe/docs/databaseref-manual.html.

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3. How can I check my routes are seen by BT Global Services?

BT Global Services Looking Glass servers

You can check how BT Global Services sees the routes you advertise by checking on the BT Global Services Looking Glass server. Select the "BGP AS path regexp" option, and click Submit. In the next page, select the country you are connecting in, and enter your AS number in the field. The output will show you all the routes the BT Global Services network knows for your AS. Verify that all of them show a path starting with your own AS number.

Any network you see there with a path starting with another AS indicates a problem -- for instance, a missing route object or an incomplete / out-of date AS number.

The BT Global Services team is currently developing an automatic notification system which will alert you by e-mail of any route advertisements presenting such a problem.

Other Looking Glass servers

You can also verify how your routes are seen from elsewhere on the Internet. The site traceroute.org lets you select where you want to look from.
Note: if you are using several providers, it is possible that those external sites will not show your routes through BT Global Services. This is because those routers select what appears to be the best route to them. Always confirm the results from those external tools with the BT Global Services Looking Glass.

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4. How do I load balance between BT Global Services and my other provider(s)?

Unfortunately, BGP does not have a clear-cut way of achieving load balancing between two or more providers. The best that can be done is some tweaking on your router's preferences to spread traffic across your various connections.

BT Global Services offers you ways to influence the amount of traffic which transits through your BT Global Services connection. They are explained in detail below. The steps are of course dependant on what your target traffic behaviour is.

For the most part, routing decisions on the Internet are made based on AS-path length; the shorter the as-path, the more preferred is the route. Some solutions proposed below use the as-path as a means to influence traffic flows from the Internet to you. However, there are a number of other parameters which individual ISP's can set in order to direct their traffic. For this reason, BT Global Services cannot guarantee that the suggestions presented here will have the desired effect.

Warning: BT Global Services assumes no responsibility for the accuracy or suitability of the solutions detailed below. Please process carefully!

  • Example 1. You want to increase the proportion of traffic from the Internet to you via your BT Global Services connection.
  • Example 2. You want to reduce the proportion of traffic from the Internet to you via your BT Global Services connection.
  • Example 3. You want to increase the proportion of traffic from you to the Internet via your BT Global Services connection.
  • Example 4. You want to reduce the proportion of traffic from you to the Internet via your BT Global Services connection.
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5. Other traffic shaping tools

BT Global Services offers you even more granularity in traffic shaping throught the use of BGP communities. You can use them to:
  1. Have BT Global Services prepend its own AS (5400) to your advertisements to some of its peers
  2. Prevent your routes from being advertised to certain peers
You can find a list of the communities and their function on RIPE, in the remarks section.

To use these communities, you need to:

  1. Create a route-map by running 
        route-map btgs-out permit 10
    set community 5400:nnnn additive
  2. Configure your peering with BT Global Services to send communities: 
        neighbor 166.49.x.y send-community
  3. Apply the route-map to your peering 
        neighbor 166.49.x.y route-map btgs-out
  4. Clear your peering with BT Global Services 
        clear ip bgp 166.49.x.y
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