Re: IXP BGP routing

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

Godinho,

I suggest we do the following:

1. Meet with TDM and convince them to:
		- Remove EIGRP or any IGP with ISPs (clients)
		- Use static routes to ISPs

2. Meet with all ISPs and convince them to use static with TDM and BGP 
(of course) with IX.

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.


rgds, a./


Brian Candler wrote:

> On Tue, May 21, 2002 at 09:34:48AM +0000, Antonio Godinho wrote:
> 
>>Hi,
>>
>>We have just set up an IXP in Mozambique but now I am having a 
>>difficult problem with the routing.
>>The ISPīs are connected to the IX directly and they peer with each 
>>other normally but the problem that has come up is that some of 
>>the ISPīs are also connected to the same Telcom for internet 
>>access. The problem is that the telcom is running EIGRP with the 
>>ISpīs and they are running BGP through the IX. Their routers 
>>always choose the EIGRP routes because of the lower admin 
>>distance of 90 over the BGP internal distance of 200 (this is 
>>because they are running iBGP between the IX router and their 
>>router). How can I change their routing so that they choose the IX 
>>routes?
>>
> 
> [Forwarded to the list with permission]
> 
> The short answer: if a Cisco gets two identical routes from two different
> routing protocols, as you have discovered it uses the "administrative
> distance" to choose between them, with the default values you have seen. You
> should be able to change them so that BGP routes are preferred over EIGRP
> routes. Someone else on this list should be able to give you the exact
> syntax if you can't find it.
> 
> The longer answer: your Telcom is leaving itself (and you) open to enormous
> risk by using EIGRP to exchange routes with its customers. Any one customer
> will be able to take down their entire network by injecting bad routing
> information. You should try to persuade them to change this situation
> _before_ their network is broken, rather than after a major outage occurs.
> 
> Possible solutions are:
> 
> (1) Use static routes - usually the preferred option if the customer does
> not have their own public AS and is not multi-homed to Telcom.
> In other words: at the Telcom router which terminates the leased line, put
> a single static route for the customer's netblock pointing down that leased
> line. EIGRP will then carry that route within Telcom's network to all their
> other routers. The customer just points a static defaultroute at Telcom.
> 
> The customer can run EIGRP, OSPF or whatever they like within their own
> network. The Telco and each customer are all running separate, isolated
> routing domains which cannot interfere with each other.
> 
>        EIGRP                             OSPF(say)
>    <----------->                         <--->
>    R ----- R     static rt                   R
>              \   --------->                /
>                R ----------------------- R
>              /                  <-------   \       BGP
>            R                     static      R --------- IXP
>                                  default
>                                            
> 
>   TELCOM NETWORK        LEASED LINE         CUSTOMER NETWORK
> 
> Since the only routes carried in OSPF are your own routes plus the static
> default, the routes for other ISPs received via the IXP will be more
> specific and therefore will always take preference (longest match wins).
> 
> (2) Use BGP (and filter the received routes)
> 
> This is the preferred solution if the customer has their own public AS,
> their own provider-independent address space, and/or is multi-homed (either
> to the same provider or to multiple providers). BGP with prefix filtering
> and flap dampening ensures that the routing domains are sufficiently
> isolated.
> 
> Regards,
> 
> Brian.
> 
> 
> 
> 
>>Cheers,
>>
>>
>>
>>Antonio Godinho
>>B.Sc., MCP, MCP+Internet, MCSE, CCNA
>>Address:Av. Julius Nyerere 947 3rd floor esq 
>>Maputo - Mozambique
>>Phone  : 258-82-300392
>>e-mail : ANTONIO at nambu.uem.mz
>>
>>An expert is one who knows more and more 
>>about less and less until he knows absolutely 
>>everything about nothing.
>>                     
>>
>>
> 
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