Re: Fundamental questions of backbone design

[Michael Hallgren <m.hallgren () free fr>]

Le 18/10/2013 20:03, Anurag Bhatia a écrit :
> Hello everyone
>
>
> I have some fundamental questions about backbone design. Feel free to point
> me to any discussions/presentation material related to these questions.
>
>
>
>    1. As I understand it's (sort off) common practice to give highest
>    localpref to customer routes then peering and finally transit. Does this
>    works well or you see issues with people who have 10+ prepends on some
>    peering routes calling you to not send traffic via those circuits? Does it
>    makes sense to put a rule to avoid routes 2-3 AS path away when changing
>    local preference?

Most often, the (``traditionally'' business driven) classification that you
mention is honored and subtler differences considered (only) in cases
where LOCAL_PREFerence is the same for some candidate routes to a
destination.

There's no ``protocol law'' ruling this, it's all your choice, that you may
base on cost, performance, or any other type of metrics that you feel
relevant... For example, you may want -- as you say -- honor the hints
from neighbors (even transitively) to route over ``less prepended
paths'' (if available) to their networks. But it's up to you, and I'd
suggest
keeping a focus on performance, path stability, neighbours reactivity
in case of failure, or some such (if you can afford it) as a metric.
Else...

>    2. If I have more peering capacity and relatively less capacity between
>    my own PoPs and I start injecting routes in my IGP then how to prevent
>    change of choking of backbone? Is it standard practice to have more
>    capacity on backbone then peering links? Or I have to inject less routes in
>    IGP - say a few % of total routes?

What routes do you inject into your IGP? Generally, it's nice to keep
IGP being merely a logical view of your graph of links, and keep
foreign/other routes in (i)BGP. Then, you need to take a look at the
distribution of your peering sessions over your sites with respect to
your customer sessions. Etc, etc,...

Backbone capacity versus peering capacity, depends on your mix
of peers, customers, providers...

>    3. How can I maintain use of routes I am learning from various other
>    networks (transit+peers+customer) across my IGP? Is BGP community tagging
>    good way out?

See above, if I understand your question correctly.

>    4. How is iBGP Vs OSPF for IGP? I keep on hearing that OSPF is good &
>    lot more faster in changing routes during a breakdown as compared to slow
>    hold time based iBGP session. Is there's more clear comparison of
>    limitations of both when designing?

Get in touch off-list, if you feel like?

Cheers,

mh

> Appreciate your time & help.
>
>
>
> Thanks.