Re: BGP sync - Why? Why not?

Hi Hammer,

In some cases, you do not need synchronization. If you do not pass traffic
from a different AS through your AS, you can disable synchronization. You
can also disable synchronization if all routers in your AS run BGP. I have
attached a good link about the subject. Other than those reasons i don't
find any reason to disable synchronization.

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800c95bb.shtml#synch

Regards,

On Mon, Nov 22, 2010 at 5:21 PM, --Hammer-- <bhmccie_at_gmail.com> wrote:

> OK. I don't see where redistribution plays into this. "no synch" simply
> allows the EGP to advertise a route to a peer w/o it being in the route
> table yet from a static or IGP. My point is that it is simply a gut check.
> If I peer up and check my routes (with synchronization on) and I don't see
> a
> route I'm looking for, I can very easily surmise that I have failed to
> introduce it via my IGP to the proper routing table. If I have
> synchronization off and I see the lack of an expected route, I have to
> troubleshoot differently. I'm trying to understand why it seems the vendors
> encourage it to be disabled. Is it a standard policy in the real lab? So we
> are just following suite? Or am I missing some adverse side affect.
>
>
>
> Again, in the big world, I understand. But this isn't the big world. This
> is
> the lab.
>
>
>
>
>
> --Hammer
>
>
>
> "I was a normal American nerd."
> -Jack Herer
>
>
>
> From: Mirco Orlandi [mailto:mirco.orlandi_at_gmail.com]
> Sent: Friday, November 19, 2010 4:14 PM
> To: --Hammer--
> Cc: miken miken; Cisco certification
> Subject: Re: BGP sync - Why? Why not?
>
>
>
> Bgp synchronization tipically requires redistribution of bgp into igp.
> Probably, (not sure) in your lab scenario you will have more than one igp
> and a redistribution plan.
> L3 loops detection/prevention is a brain-intensive task. Taking care of
> extra external routes may result in wasting time (bgp->igp1->igp2->igp1 =
> loop).
>
> -mirco.
>
> On Fri, Nov 19, 2010 at 5:47 PM, --Hammer-- <bhmccie_at_gmail.com> wrote:
>
> Absolutely. For real world (Internet, big WAN, etc.) I can see it as
> suboptimal. I'm just struggling with it in the context of practice labs and
> the impending real lab.
>
>
>
>
>
>
>
>
> --Hammer
>
>
>
> "I was a normal American nerd."
> -Jack Herer
>
>
>
>
> From: miken miken [mailto:miken_at_sisna.com]
> Sent: Friday, November 19, 2010 10:13 AM
> To: --Hammer--
> Cc: Cisco certification
> Subject: Re: BGP sync - Why? Why not?
>
>
>
>
> The simplest explanation I have found for real world scenarios is given by
> Philip Smith from Cisco in his presentation that can be found on the NANOG
> website. He states that it is not feasible to wait for the ~222,000
> prefixes
> to synchronize in IGP (OSPF/ISIS) before BGP will select the path. You can
> hear this explanation about 1:11 into the presentation. However, I do not
> know how to apply this to the lab, other than best practice??
>
> Thank you
> MikeN
>
> On Fri, Nov 19, 2010 at 8:39 AM, --Hammer-- <bhmccie_at_gmail.com> wrote:
>
> OK, I understand what synchronization is and how it works. So, all the
> videos/audios/labs/etc. always say to explicitly disable it (I know it's
> disabled by default). What I'm struggling with is why? If the end all
> result
> of a lab is "full" reachibility and the lab doesn't disallow
> synchronization, then isn't it helping us? I know I'm missing the big point
> here but I don't see why it's a bad thing. Can someone enlighten me? The
> byproduct would be that your troubleshooting might be a little different..
>
>
>
>
>
>
>
> --Hammer
>
>
>
> "I was a normal American nerd."
> -Jack Herer
>
>
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-- 
KJ
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