[c-nsp] BGP for multi-homed environment

[Carlson Per]

Hi Alex.

Welcome to the wonderful world of BGP! 

> I want to connect each feed into a separate router and 
> load share from my network. First off - is this possible??  

Yes it is, but require some fiddeling around with BGP. Normally
outbound traffic is easier to loadshare than inbound.

> I have been allocated a class C address block. 

Hmm, that limits some of your options for inbound traffic.
More about that later.

> I also want the ability to provide seamless failover between 
> both providers.  I am also a little unsure as to what is required 
> with regards to filtering etc;  what is the best policy here??

As a starter, filter out announcement that you *know* is faulty.
For you that means prefixes not allocated by IANA (here is a
terific link: http://www.cymru.com/Bogons/). If you are getting
full internet routes, filter out the default route as well.
Cymru also has got an extensive example of secure BGP configuration:
http://www.cymru.com/Documents/secure-bgp-template.html

If your router supports it, use URPF
(http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_configurati
on_guide_chapter09186a00800ca7d4.html)

I would also recommend ACL's that filters out traffic entering
and leaving your network. You can more or less filter out all 
traffic not destined to/sourced from your Class C-network. 
Don't forget to permit BGP-traffic to the IP-adress of your
peering point!
  
> If anybody implements a similar configuration - I would 
> appreciate some tips or feedback.

I would recommend you to start of with no BGP-policy at all.
If that's works out for you, fine, if not, you have to set up
a policy.

For outbound traffic, you have two basic options, local preference,
AS-prepends. 

To loadbalance inbound traffic you can use AS-prepends and and splitting 
up the network. The latter is not available for you, prefixes that's 
25 bits and longer is very often filtered out by other operators
BGP-policies. 

If you already havn't got it, I can warmly recommend the book
'Internet Routing Architecture' by Sam Halabi:
http://www.ciscopress.com/title/157870233X

Per