From: Brian Lodwick (xpranax@xxxxxxxxxxx)
Date: Fri Mar 08 2002 - 13:53:06 GMT-3
Robert,
One scenario I can think of for sure would be if the customer will have a
multi-homed approach to internet connectivity more than one ISP. BGP is then
needed to manipulate the ISP's routing decisions. I suppose you could still
use the statics and redistribution on each ISP approach, but then you would
not have any control.
Another scenario that I will always implement BGP on is a customer that has
what we call a dual / shadow solution. Where there will be 2 edge routers on
the customers network that connect to 2 different gateway routers on the ISP
network, and one is to be designated as the primary and one as the
secondary. If I were to use static routes and redistribution in this
schenario the 2 ISP gateway routers would be redistributing these routes
without any other routing information, so I would not be able to designate
one as the Primary and one as the Secondary if I didn't send the routes
through BGP with MED's.
This situation is similar, but is a different issue. Same situation meaning
if the customer has 2 connections to the ISP and these 2 connections go from
2 different edge routers on the customer network to 2 different Gateway
routers on the ISP's network. Now factor in let's say an ethernet connection
off of the back side of the customers edge routers to another
router/firewall. We want to make sure that inbound traffic will not be sent
to a customer edge router if it's ethernet connection is down. We can use
some kind of redundancy protocol on the ethernet such as VRRP, HSRP, or a
routing protocol to control outbound traffic, but to control inbound traffic
you must have some way to alert the ISP's gateway router to go over the
correct link (the one with an up ethernet interface) or else all inbound
traffic will be dropped. If you do not use BGP to communicate this, the
ISP's gateway router will not have any way of knowing not to send traffic to
the router with the down ethernet connection because the serial link will
still be up and the static route will still be valid and redistributed.
Therefore BGP is required in this scenario to influence inbound traffic to
the customer site in response to a LAN connection outage on the customer
edge router.
I can't think of any other situations right now where BGP would be required.
Several make the use of BGP attactive, but required is small. I remember in
Halabi's BGP book he goes over several scenarios. May prove to be a good
reference for you?
>>>Brian
>From: "McCallum, Robert" <Robert.McCallum@let-it-be-thus.com>
>Reply-To: "McCallum, Robert" <Robert.McCallum@let-it-be-thus.com>
>To: "'Ccielab' (E-mail)" <ccielab@groupstudy.com>
>Subject: WHY BGP
>Date: Fri, 8 Mar 2002 15:25:22 -0000
>
>Question.
>
>Why would a company want BGP?
>
>In what scenarios would it be good working policy to actually sell them BGP
>instead of advertising their netblock through redistribution means and
>giving them a default route.
>I have struggled with this question for a while and I can't really come up
>with any hard evidence to the benefits of BGP for a customer.
>
>I mean what does BGP give a customer?
>
>Any thoughts welcome
>
>Robert McCallum CCIE #8757
>Data Network Engineer
>Ext 730 3448
>DDI : 01415663448
>Mobile : 07818002241
>
>"You can swim all day in the Sea of Knowledge and
>still come out completely dry. Most people do."
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