RE: bgp 2 isp question

And here are the community guides for the majority of providers. It still
may be a service they need to enable / accept on their end.

http://www.onesc.net/communities/

--
http://dcp.dcptech.com
> -----Original Message-----
> From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
> Tech Guy
> Sent: Tuesday, August 31, 2010 11:58 PM
> To: Paul Negron
> Cc: Fake Name; Tyson Scott; Cisco certification
> 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
> >>>
> >>>
> >>> Blogs and organic groups at http://www.ccie.net
> >>>
> >>>
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