[c-nsp] BGP long prefix ads

[Roman Bestuzhev]

Hello All,

Thanks for comments, will digg BGP communities.

2008/1/12, Jon Lewis <jlewis at lewis.org>:
>
> On Fri, 11 Jan 2008, Roman Bestuzhev wrote:
>
> > I am thinking about load balancing between both ISPs. I have read about
> a
> > technique when you divide your block to several pieces, for example to
> two
> > /22 blocks and advertise one of them to one ISP and other block to
> another
> > ISP and at the same time advertise whole prefix to both ISPs, /21 in
> this
> > case. This leads to getting incoming traffic trough both providers and
> you
> > can control which subnets in your AS connect to Internet trough which
> ISP.
>
> You can probably achieve some level of load sharing without resorting to
> polluting the DFZ.  First thing to look at is relative as-path length.  If
> provider A is more of a "Tier 1" provider than provider B, then you might
> try prepending your ASN once on announcements to A.
>
> If A supports it, you may be able to use community tagging to tell them to
> do some prepending when your route is propogated to certain peers, thus
> causing those peers to be more likely to use your B provider path.
>
> If you do resort to chopping up your CIDR, make sure you announce both the
> aggregate and subnets...so those who filter those sorts of "garbage
> routes" can do so without losing connectivity to your network.
>
> > My question: is this scheme used widely and would this scheme work well
> in
>
> Used widely and correct/advisable are different things.  Lots of networks
> announce their CIDRs as individual /24s.  It doesn't mean you should.
>
> ----------------------------------------------------------------------
>   Jon Lewis                   |  I route
>   Senior Network Engineer     |  therefore you are
>   Atlantic Net                |
> _________ http://www.lewis.org/~jlewis/pgp for PGP public key_________
>



-- 
Roman Bestuzhev,
System Administrator