See comments below:
> I haven't worked with BGP yet, so someone please correct me if I'm wrong
> with this -
>
> My understanding is that even if you have internet connections to two
> differnet ISPs, you don't have to BGP. If you are using IP addresses they
> have assigned to you then you are ok.
It depends what "ok" means for you. If you need redundancy and backup,
then you are not "ok". Consider the scenario below :
|-------| |-----------| |-------|
|
| ISP1 |---------------| Customer |-----------| ISP2 |
| | | | | |
| AS1 | | | | AS2 |
|-------| |-----------| |-------|
The customer is multihomed to AS1 and AS2. The customer is not running BGP
in this scenario.
Suppose ISP1 has assigned the customer 10.10.10.0/24 and ISP2 has
assigned the customer 10.10.11.0/24. Both ISPs are statically routing
those blocks to the customer. The customer has two default routes, one to
each ISP (he could prefer one ISP or the other for outbound traffic but
inbound traffic will come from ISP1 or ISP2 depending on the destination
ip address).
Inbound traffic destined for hosts in 10.10.10.0/24 comes through ISP1 as
ISP1 is originating and advertising this block. Inbound traffic destined
for hosts in 10.10.11.0/24 comes through ISP2 as ISP2 is originating and
advertising this block.
Now what happens if the connection between the customer and ISP1 goes down
for any reason ? Well you will see that hosts in 10.10.10.0/24 will be
unreachable from outside the customer's network. So redundancy is not
achieved properly as half of the customer's network will be down.
> The big reason to use BGP would be if you have a block of registered IP
> addresses and you want to advertise them to the internet via two different
> ISPs.
I would say that as soon as you are multihomed (to 2 different providers)
then using BGP is a Must. (Of course if you really want total redundancy
and the option to do intelligent routing, load-sharing..).
>
>
> >
> >Hellow group!!
> >According to cisco press book, when company has two connections active to
> >two different ISPs, BGP should be used.
> >Could anybody tell me what is the result of connecting two active
> >connections to two different ISPs?
> >I know that one connection should be used as a backup line only while the
> >other is active in order not to use BGP.
> >Thanks in advance.
> >
> >........................................................
> >iWon.com http://www.iwon.com why wouldn't you?
> >........................................................
> >
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--
Contrary to popular belief, Unix IS user friendly. It just happens
to be very selective about who it decides to make friends with.
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Andre Riscalla Network Specialist - Internet
[EMAIL PROTECTED] 514-940-5664
Network Engineering AT&T Canada
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