Re: IXP BGP routing

[Noah K Sematimba <ksemat at wawa.eahd.or.ug>]

> Perhaps a diagram will help:
>
>                                         --- ISP2
>                   satellite           /
>       Internet <----------------- ISP1 ---- ISP3
>                                    |
>                                   IX
>                   satellite        |
>       Internet <----------------- TDM ----- ISP4
>                                      \
>                                        ---- ISP5
<snip>
> Of course, ISP's 2 to 5 may decide to set up their own private peering with
> each other at the IX, to reduce chargeable traffic on their uplinks.
>
> However, in general, ISP1 will not be interested in peering with ISP4 and 5.
> That's because:
> (a) there is no cost saving - traffic to ISP4 and 5 already goes via the IX
>     (via TDM)
> (b) there is an additional cost in maintaining these extra peering
>     relationships
> (c) there is loss of revenue to TDM. Politically you don't want to cut off
>     the revenue streams of people at the same "tier" as you in the game,
>     because you don't want them to do the same to you.

On the other hand if as is prevalent in Africa TDM is providing rather
lousy service, or the link via TDM is congested, ISP1 may consider peering
with 4 and 5 over their separate links to the IX.

It is still in ISPs 2-5 interests for them to peer with each other. and
leave the decision to the tier 1 ISPs on whether they would like to peer
with them.

Noah.


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