Re: IXP BGP routing

["Americo F. Muchanga" <americo at it.kth.se>]

Brian,

u got me wrong, what i was trying to explain is why TDM (yes telco) will 
peer although is not a traditional ISP.

Brian Candler wrote:

> 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.




yes but if ISPs using TDM do not peer, then they'll share international 
and local traffic in the same link. Say ISPs locally produce alot of 
traffic to that particular ISP, then users searching for information 
from outside the country will perceive bad quality of service, while 
congestion is caused by local traffic. The advantage of having that ISP 
to peer is just that he can grow his local link independently of the 
international link for which he pays every kbps.


> 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.


TDM do not loose money, they always have money. They are the only one 
connecting other ISPs all the others have independent links.


> 
> 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.


No, Digital agencies are different from ISP 4/5, digital agencies are 
run by TDM, while ISP 4/5 would be a true ISP. The main difference is 
just that TDM no longer provides Internet to itself and ISPs but has 
chains of what you could call cybercafes.



hope i have clarified.

rgds, a./

 
> 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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