Re: BGP Traffic Engineering - Active\Passive

[Chriztoffer Hansen <ch () ntrv dk>]

On Fri, 21 May 2021 at 17:13, nanoguser100 via NANOG <nanog () nanog org> wrote:
> If I'm unable to do that will most provider prepend on your behalf so that ISP-A would add the prepends for 9999 only?

For this part, you will have to investigate which BGP
standard/extended/large communities your ISP-A/B supports.

By setting the correct community, your upstream can do the prepending
for you. (usually 1, 2, or 3 times depending on the supported
communities)

E.g.
* ISP-A 1111 174 4444
* ISP-B 1111 1299 1299 4444
or
* ISP-A 1111 174 174 174 4444
* ISP-B 1111 1299 4444

> Now to mix this up let's say another ASN, 7777 was in-between 1299 and 9999 but latency wise the route was still 
> faster.

Some(!) ISP's will support _only_ prepending to select ASN's they peer with.

E.g.
* prepend only to peers
* prepend only to customers
* prepend only to other upstream (in case of T2 and T3)
* prepend if a route is exported outside $region-Y
* prepend to ASN xxxxx 1-time
* prepend to ASN xxxxx 2-times
* prepend to ASN xxxxx 3-times

E.g.
* ISP-A 1111 174 174 174 65001
* ISP-A 1111 174 174 174 65002
* ISP-A 1111 174 174 174 65003
* ISP-A 1111 174 7777
* ISP-B 1111 1299 1299 7777

You will need to investigate which BGP communities your ISP's support
for the above example to be relevant to you. If they do not have the
docs available on their public website or customer portal. Ask their
support for a list of supported communities.

/Chriztoffer