Subject: Re: [Idr] Next Hop changes

From: "john smith" <[email-masked]>
Date: Sat, 10 Jul 2004 10:23:08 +0000

I am amazed no one has answered to this post.

I have never seen the changes in BGP causing changes in IGP, as we rarely 
ever have cases where people do BGP-->IGP. It would bring down your network 
though :)

I also feel that the concept of things like HOT Potato come into play only 
in the case when 1 protocol has to depend on the other. Though, if I look up 
the defination of Hot Potato in some classic books like Data Networks by 
Robert Gallager and Dimitri Bertsekas , it does not seem to be what is 
referred to as "Hot Paotato" in some other papers and discussions that I 
see. The case and examples in the books never talk about multiple protocols 
to put forth the point of Hot Potato routing.

Perhaps someone could help clarify the definations in the 1st place,

-brgds
JS

>From: "ephim  era" <[email-masked]>
>Reply-To: ephim  era <[email-masked]>
>To: [email-masked]
>Subject: Re: [Idr] Next Hop changes
>Date: 10 Jul 2004 09:54:20 -0000
>
>
>
>
>On Wed, 07 Jul 2004 ephim  era wrote :
> >Hi All,
> >
> >Is there a scenario (protocol, deployment, configuration) wherein a 
>change in BGP nexthop could lead to sea of changes in IGP routes (or 
>vice-versa) ?
> >
>
>  case excluding redistribution of routes... ?
>
> >Thanks in advance,
> >Ephim
> >
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---

From: Tony Li <[email-masked]>
Date: Sat, 10 Jul 2004 12:29:36 -0700

I'll try to answer both:

1) A change in BGP next hops should never lead to a change in IGP 
routes unless someone is doing redistribution.  It _can_ of course,
change how traffic flows internal to the domain.

2) Hot potato routing is also known as "nearest exit".  The basic 
philosophy is that a transit provider wants to hand off the traffic
with the fewest number of fiber miles/router hops/overall expense.  
Multiple protocols are not required.

Tony

On Jul 10, 2004, at 3:23 AM, john smith wrote:

> I have never seen the changes in BGP causing changes in IGP, as we 
> rarely ever have cases where people do BGP-->IGP. It would bring down 
> your network though :)
>
> I also feel that the concept of things like HOT Potato come into play 
> only in the case when 1 protocol has to depend on the other. Though, 
> if I look up the defination of Hot Potato in some classic books like 
> Data Networks by Robert Gallager and Dimitri Bertsekas , it does not 
> seem to be what is referred to as "Hot Paotato" in some other papers 
> and discussions that I see. The case and examples in the books never 
> talk about multiple protocols to put forth the point of Hot Potato 
> routing.
>

---

From: Curtis Villamizar <[email-masked]>
Date: Sat, 10 Jul 2004 20:11:39 -0400

> ever have cases where people do BGP-->IGP. It would bring down your network 

What's the question you are looking to get answered?

> Perhaps someone could help clarify the definations in the 1st place,

I have no idea who Gallager and Bertsekas are or what they wrote but I
think Sean Doran or Peter Lothberg originally referred to using the
IGP cost criteria in BGP MED as "hot potatoe" and passed across
providers as "cold potatoe" (what a legacy).  The definition should be
clear in draft-ietf-idr-bgp4-experience-protocol-04.txt in Section
7.1.1. "MEDs and Potatoes".

Curtis

ps - I like the paragraph:  

   Seemingly more intuitive references that fall outside the vegetable
   kingdom refer to cold potatoe routing as "best exit routing", and
   hot potatoe routing as "closest exit routing", though vegetable.

but it looks like the last two words don't belong there or were part
of something truncated like "though vegetable terminology was at least
initially much more common" (which we could probably drop anyway).

---

From: Danny McPherson <[email-masked]>
Date: Mon, 12 Jul 2004 07:47:12 -0600

> initially much more common" (which we could probably drop anyway).

Yep, I cleaned this up in the last version, which I still
need to post..

And I indeed wasn't referring to buffers, queuing, store &
forward, et al., though there is clearly underlying relation.

-danny