[c-nsp] BGP route won't advertise

[Mattias Gyllenvarg]

Just too add...

With communities you make your own rules. As in Petes example you make up
what numbers you want and how they look.

In Petes example he uses the most common way of implementing this. Which is
a single large community number with several purposes.

In our design, which I have not seen anyone else do, we have many
communities per prefix that has an individual purpose each.

Plus side is no complex regexp that can be hard too design and troubleshoot.
Minus is more communities.

Our cheat sheet looks something like.

100-199 What ISP originated?
200-299 POP
600-650 How too announce
etc etc

I think and the guys here (at work, not the list) agree that this is easier
too work with.

Don't fall into the "make it complex because you can" trap. Its hard too
get out...


On 6 March 2013 15:16, Pete Templin <petelists at templin.org> wrote:

> On 2/28/13 10:35 AM, Jerry Bacon wrote:
>
>  It's complicated. I am doing transit for this customer, be we have
>> common upstream peers, and I need to disallow his other advertisements.
>> I'm sure there are better ways to do this, but my real problem is that I
>> can't get one of my routers to advertise his routes, while the other one
>> does.
>>
>
> Jon is right, deny or allow+tag is the way to go.
>
> Simple example: "ASN" in this case is your ASN.  Make a cheat sheet like
> this: ASN:ABCDE.  The right side breaks out to:
>
> A (route category) = 1 for customer, 2 for "yours", 3 for upstream
> BC = pop number, set to 01 for now if you want a starting point.
> DE = future expansion, set to 00 for now as a starting point.
>
> This customer's routes would get tagged ASN:10100, your own aggregates
> would get tagged ASN:20100, and upstream routes would get tagged ASN:30100.
>
> ip community-list 101 permit ASN:1....
> ip community-list 102 permit ASN:2....
> ip community-list 103 permit ASN:3....
>
> route-map transit-out p 10
>  match commu 101
> route-map transit-out p 20
>  match commu 102
> route-map transit-out d 30
>  match commu 103
>
> Bingo, this prefix goes out, but other routes from that customer's AS
> (learned from one transit) don't flow to the other transit.
>
> pt
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*Med Vänliga Hälsningar - Best Regards*

*Mattias Gyllenvarg*
*Nätutveckling*
Bredband2

Tel: +46 406219712