Hi Jason,
Customer multihoming is as much about figuring out configuration as it is
about solving the "political" problems between the ISPs with that customer.
Many service providers don't venture down that path, and some have very
strict policies regarding multihoming.
If you and the other ISP being used by your customer for multihoming can
actually agree on configuration, you should be able to set up multihoming
for your customer without impacting the Internet routing table (which has
start to grow exponentially again, btw).
There are two scenarios:
- if your customer is looking for link or ISP edge redundancy, and you
have a peering with their proposed multihoming partner, then your problem
is easy to solve. Both upstreams have assigned address space to the
customer, they announce this address space to each other, the customer uses
BGP with a private AS. And as this is a Cisco list, I'll point you at the
BGP Conditional Advertisement feature, which also helps with this. The
bottom line is that as far as the Internet is concerned the customer looks
like two normal statically connected connections. No public ASN is
required. No /24s are leaked to the Internet, no harsh flap dampening, no
concern about reachability - a good thing.
- if your customer is looking for ISP redundancy (ie, if one ISP's entire
backbone vanishes you are relying on the other one for Internet
connectivity), then the problem is harder to solve cleanly. Both ISPs will
have to announce /24s to the Internet, and this in many people's opinions
is a bad thing - see above.
The key is forming an agreement between you and your customer's proposed
peering partner. I'd imagine that if this is in Singapore this should be
fairly possible, and hopefully you can work out a configuration which will
benefit your customers as well as the Internet...
I hope this helps...
philip
--At 22:25 08/08/00 +0800, Jason Lim wrote: >Hi all, > >Actually, I need advise in dual-homing policy with our lease line >customers. We have encountered some issues on lease lines customers >wanting to dual-home their connection with our ISP(ISP1) and other >ISP(ISP2) and this demand is growing. For example, a customer with two >connection to ISP1(AS100) and ISP2(AS200) would be getting 203.222.100/24 >from ISP1 and 155.169.22/24 from ISP2. Customers wants redundency by >asking ISP1 to advertise 155.69.22/24 and ISP2 to advertise >203.127.100/24 as well. > >The reasons why it's an issue because > >1) These customers are not running BGP. I understand that conditional >advertisment with BGP can solve the problem. >2) These customers wants ISP1 to advertise IPA blk which belong to >other ISP2 and likewise for ISP2 to advertise ISP's IPA > >Well, currently there is now no mutual agreement with other ISPs to do so. > >I would like to know : >1) How will like to know how will it impact ISP1 and ISP2 in term of >routing advertisment,tables,etc ? >2) Will ISP1 and ISP2 have problems of routing holes for advertising >routes belonging to other ISPs' ASes. > >I am not sure if there are any other technical implication. >How does other ISPs in US or other parts of the world >dual-homed their customers' who do not run BGP(only statics route)? > What are the pros/cons of doing/not doing this ?? > >Thank you very much >Regards >Jason >SingNet NOC >Network Engineer
-------------------------------------------------------- Philip Smith ph: +61 7 3238 8200 Consulting Engineering, Office of the CTO, Cisco Systems --------------------------------------------------------
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