Re: bgp 2 isp question

I understand this disagreement. However, YOU do get to dictate to the
provider what you want MOST of the time.(If you know what you are doing.)
:-)

So far, I have NEVER had a problem. (fingers crossed)

That said, I do agree with this line of reasoning since I have and still do
practice it. It is just one tool in the belt though.

I have just worked with enough providers to know how incompetent they can
be. Regardless of the policies they set. (REAL LIFE). You need to remember
layer 8, especially with BGP.

I do agree that the advice given by Tech Guy is the best MOST of time. I
just used AS path prepending successfully last week, but that is not saying
that I use it as a first option every time.

This is the type of dialogue that I love on groupstudy. There should be
different views on BGP if we are doing it right.

Paul

-- 
Paul Negron
CCIE# 14856 CCSI# 22752
Senior Technical Instructor
www.micronicstraining.com
> From: Tech Guy <autechguy_at_gmail.com>
> Date: Wed, 1 Sep 2010 13:58:09 +1000
> To: Paul Negron <negron.paul_at_gmail.com>
> Cc: Fake Name <fname84_at_gmail.com>, Tyson Scott <tscott_at_ipexpert.com>, Cisco
> certification <ccielab_at_groupstudy.com>
> Subject: Re: bgp 2 isp question
> 
> I have to disagree with both Paul & Tyson.
> 
> My real word answer is that AS-prepend will not always do the job for
> you (no matter how many you prepend), when you want to use the second
> ISP connection purely as the backup.
> 
> This is because the ISP may by default always prefer the routes
> advertise from their customers, over the one learnt from other ISP and
> the Internet, disregard of the AS path. The end result is that they
> will always send traffic back to you via the direct peering. This is
> particular true if the ISP config follows the RFC1998. In this case,
> if you want to use the second ISP connection as backup you need to
> send them an agreed community to lower their local preference. You'd
> better check with both ISP for their specific design guideline.
> 
> My best practice (without having to worry about the ISP design) is to
> send more specific (/24 subnets) to the primary ISP, and only the
> summary (/23) to the second ISP. The config you proposed is OK, but
> you need to make sure that you have outbound prefix-list or route-map
> to stop /24 from being advertised to the second ISP. By default,
> without those filter-list (assuming your two routers have iBGP peering
> with each other) both /24 and /23 will be advertised to both ISP, and
> you will not get the desired goal.
> 
> 
> More info on RFC1998 below
> 
> http://tools.ietf.org/html/rfc1998
> 
> 4. A Real-World Implementation Example
> 
>    MCI currently makes heavy use of the BGP "LOCAL_PREF" attribute value
>    as part of its routing policy configuration process.  Different BGP
>    "LOCAL_PREF" values are assigned for routes from different sources.
>    Table 1 details these values:
> 
> 
>                   +-------------------------+------------+
>                   |        Category         | LOCAL_PREF |
>                   +-------------------------+------------+
>                   |Customer Routes          |        100 |
>                   |Customer backup Routes   |         90 |
>                   |Other ISP Routes         |         80 |
>                   |Customer-Provided backup |         70 |
>                   +-------------------------+------------+
> 
>                     Table 1: Defined LOCAL_PREF Values
> 
> 
> 
> On Wed, Sep 1, 2010 at 10:24 AM, Paul Negron <negron.paul_at_gmail.com> wrote:
>> In the real world, you would start with about 3 prepends and add one at a
>> time until you get the desired result. Once you get what you need, you would
>> maybe add another for good measure. This method has been proven to be quite
>> successful for me over the last 12 years in the Service Provider
>> Environment. Just my experience and 2 cents worth. :-)
>> --
>> Paul Negron
>> CCIE# 14856 CCSI# 22752
>> Senior Technical Instructor
>> www.micronicstraining.com
>> 
>> 
>> 
>>> From: Fake Name <fname84_at_gmail.com>
>>> Reply-To: Fake Name <fname84_at_gmail.com>
>>> Date: Tue, 31 Aug 2010 13:53:22 -0400
>>> To: Tyson Scott <tscott_at_ipexpert.com>
>>> Cc: Cisco certification <ccielab_at_groupstudy.com>
>>> Subject: Re: bgp 2 isp question
>>> 
>>> Tyson
>>> 
>>> Thanks for the response.  Let me ask you in the real world how many times
>>> would you prepend your as onto it to make it less perfered?
>>> 
>>> 
>>> 
>>> 
>>> On Tue, Aug 31, 2010 at 12:26 PM, Tyson Scott <tscott_at_ipexpert.com> wrote:
>>> 
>>>> Yes that will work or you can use path prepending to make the AS-PATH
>>>> shorter for the one you want.  Both are typical scenario's used on the
>>>> internet.
>>>> 
>>>> Regards,
>>>> 
>>>> Tyson Scott - CCIE #13513 R&S, Security, and SP
>>>> Managing Partner / Sr. Instructor - IPexpert, Inc.
>>>> Mailto: tscott_at_ipexpert.com
>>>> 
>>>> 
>>>> 
>>>> -----Original Message-----
>>>> From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
>>>> Fake
>>>> Name
>>>> Sent: Tuesday, August 31, 2010 12:06 PM
>>>> To: Cisco certification
>>>> Subject: bgp 2 isp question
>>>> 
>>>> If i have a /23 block and I have two isps and 2 different routers.  I want
>>>> to perfer traffic to come into 1 router for the block opposed to the other.
>>>> From what I understand /24 is the highest mask that wont be summarized.
>>>> 
>>>> All traffic should come into router1 untill it is down then traffic will
>>>> come into router 2 because they have more specific routes correct?
>>>> 
>>>> 
>>>> Router1 most perfered
>>>> ip route x.x.x.x x.x.x.x (next hop) 0
>>>> ip route x.x.x.x x.x.x.x (next hop) 0
>>>> router bgp x
>>>> network x.x.xx.x 255.255.255.0
>>>> network x.x.x.x 255.255.255.0
>>>> 
>>>> Router2 less perfered
>>>> ip route x.x.x.x 255.255.254.0 (next hop) 0
>>>> router bgp x
>>>> network x.x.x.x 255.255.254.0
>>>> 
>>>> 
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>>>> 
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>>> 
>>> 
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>> 
>> 
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