Re: IXP BGP routing

[antonio at nambu.uem.mz]

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I guess one of the reasons the ISP's under TDM (telco) will and are 
connecting to the IXP is that they will have a link that carries the local 
traffic and one that carries international traffic. This may seem 
unecessary but when telco provides 64K and 128K links to the ISP's 
it kind of becomes a need. The local and international traffic from the 
provider to the telco are taking one link and saturating it. When the 
telco decides to connect to IXP I guess the ISP will just use local 
preference to choose the IXP link for local traffic.

Cheers,



> On Tue, May 21, 2002 at 11:49:53PM +0200, Americo F. Muchanga wrote: >
> 2. Meet with all ISPs and convince them to use static with TDM and BGP
> > (of course) with IX.
> 
> TDM = your telco?
> 
> > Info for outsiders, TDM will peer at the IX not only to exchange
> > traffic with those ISPs who do not use TDM as gateway but also
> > because TDM do have users that get Internet Services through TDM.
> > TDM has a network of cybercafes and now are deploying what they call
> > as Digital Agencies (50+). If TDM did not peer, for those users to
> > access websites from, say CIUEM, Teledata, etc, traffic would have
> > to go to US or Europe.
> 
> I don't understand what you are trying to say there.
> 
> Traffic from a TDM customer (downstream) to another TDM customer will
> always go via TDM - it will never go via US/Europe.
> 
> Traffic from a TDM downstream to an ISP which has an independent
> uplink will take the 'short' route via the IX if TDM peers with that
> ISP. It is not necessary for the downstream itself to peer. When TDM
> peers, it will announce all the routes of its customers.
> 
> Perhaps a diagram will help:
> 
>                                    --- ISP2
>                   satellite           /
>       Internet <----------------- ISP1 ---- ISP3
>                                    |
>                                   IX
>                   satellite        |
>       Internet <----------------- TDM ----- ISP4
>                                    \
>                                    ---- ISP5
> 
> At the IX, ISP1 will announce its own routes and those for ISP2/3 [*].
> TDM will announce its own routes and those for ISP4/5.
> 
> Traffic from ISP2 to ISP5 will go ISP2->ISP1->TDM->ISP5, no satellite
> hop is required, even if ISPs 2-5 are not IX members.
> 
> 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.
> 
> Within Mozambique, you could call TDM and ISP1 "tier 1" ISPs (those
> with their own International links), whilst ISP2-5 would be "tier 2"
> ISPs.
> 
> So, if I understand your paragraph above correctly, "Digital Agencies"
> = ISP4/5. For local users of any other ISP to reach those sites using
> the 'short' route via the IX, TDM only needs to peer with other tier 1
> ISPs.
> 
> Regards,
> 
> Brian.
> 
> [*] If the ISP 2 or 3 has their own public AS, then their routes will
> be announced with the ISP's AS in the path. If they don't, then the
> route will be announced from ISP1's AS. If ISP 2 or 3 does not have
> provider- independent address space but gets their IP addresses from
> ISP 1 then their route will be aggregated within ISP1's own
> announcement anyway.



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Antonio Godinho
B.Sc., 
MCP, MCP+Internet, MCSE (Microsoft Certified Systems Engineer)
CCNA (Cisco Certified Network Associate)
Tel. +258-1-490860
Cell +258-82-300392


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