[c-nsp] BGP long prefix ads

[Christoph Loibl]

Hi Roman!

On Jan 11, 2008, at 10:16 AM, 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.

Network equipment manufacturer may like this approach as this pushes  
the market demand for new routing-hardware as the full internet  
routing table increases dramatically (and old equipment may not be  
able to handle that size of routingtables anymore). ISPs generally  
won't be so happy with that (but mostly already replaced their  
equipment, or found ways around - see also the threads "internet  
routingtable already too large for sup720-3b, sup2, ..." on this list).

But to answer your question:

> My question: is this scheme used widely and would this scheme work  
> well in
> real Internet for /22 prefixes, for /23? For example, is there any

When you look at the current internet routing-table you may find many  
of those more-specific announcements. In general this will work in  
the internet (depending on where/how you connect).

> possibility to loose connectivity to some parts of Internet in case of
> filtering of long prefixes by Internet Providers? Are there other  
> drawbacks
> of this?

You should make sure to announce the /22 aggregate all the time, and  
additionally inject those more specific, if you want to make sure  
that even when your more specific routes get filtered, your network  
is reachable. But I would not suggest that approach for the reason  
mentioned above. The stability of whole network does not increase  
when we have more routes (but I can't prove that it decreases either).

> Thanks in advance for any ideas and advises,

Did you ever think about simply not prepending your AS to the backup- 
provider? This may also lead to ("some") incoming traffic taking the  
backup-connection while not adding any additional routes to the  
internet-routing table. But this approach depends very much on the  
connectivity of you network-providers you are not able to control  
which destinations within your network are reachable via which of  
your network-providers. Anyway I would suggest to give it a try  
first. It may do the job for you.

Stoffi

-- 
CHRISTOPH LOIBL ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
mailto:c at tix.at   |No trees were killed in the creation of this message.
http://pix.tix.at |However, many electrons were terrible inconvenienced.
CL8-RIPE ++++++++++++++++++++++++++++++++++++ PGP-Key-ID: 0x4B2C0055 +++