From: Pavel Bykov (slidersv@gmail.com)
Date: Fri Jan 23 2009 - 17:22:07 ARST
Ronnie,
The scenario I was thinking of first was the following, but for it to work
you would have to summarize between distribution switches, which would be
kind of... well.. incorrect.
Imagine the access switch having /24 subnet.
Now, we are summarizing the /24 on the distribution for the simplicity sake
to /16.
Scenario 1 with failure in document: link between Distribution is outside of
address range.
Left distribution has connectivity, and therefore /24 and /16. Right
distribution lost connectivity and has only /16, it does not have any other
route to /24 at all. All it has is /16 summary, and even if it leads to left
distribution switch, it has to first to confirm that there is no /24
anywhere else and send query out interfaces without summaries (other access
switches, if present). Therefore it has to converge.
Scenario 2 with failure in document: link between Distribution is within the
address range.
Left distribution has connectivity, and therefore /24 and /16. Right
distribution lost connectivit, but has FS from left distribution! PtP link
was within the summary scope, so there was no summary going there.
So yeah, the "effective" then seems to refer to query scope only.
On Fri, Jan 23, 2009 at 8:00 PM, Ronnie Angello <ronnie.angello@gmail.com>wrote:
> As long as a feasible successor exists, EIGRP will not go active on
> the route and will start using the feasible successor immediately.
> That behavior is independent of how links are addressed. I don't
> recall seeing a requirement that the link has to be within the same
> address space. That's news to me so I was trying to figure out
> exactly why.
>
> The only thing that I can think of is that the whole point of the
> summary is to contain the query scope. If the distribution link is
> within the range of the summary, then it's advertised to the core as
> part of the summary and you don't have to worry about the rest of the
> network being queried if that link fails.
>
> On Fri, Jan 23, 2009 at 1:53 PM, ISolveSystems
> <support@isolvesystems.com> wrote:
> > But even if the p2p link between the dist switches is NOT within the
> range
> > that's being summarized, why is there a need for convergence for the p2p
> > link IP address when the access layer link is failing (not the P2P link)?
> > The query will not go out for the p2p link, but just for the access-layer
> > subnet, right?
> >
> > Thanks.
> >
> > On Fri, Jan 23, 2009 at 11:21 AM, Pavel Bykov <slidersv@gmail.com>
> wrote:
> >
> >> Because otherwise you wouldn't be able to reroute traffic from the right
> >> distribution switch to the access immediately - you would have to wait
> for
> >> IGP convergence.
> >> If ptp link between distribution switches is WITHIN the range that is
> being
> >> summarized, you don't wait for a convergence, and use feasible successor
> >> route INSTANTENEOUSLY
> >>
> >> On Wed, Jan 21, 2009 at 10:30 PM, ISolveSystems <
> support@isolvesystems.com
> >> > wrote:
> >>
> >>> I am reading the campus network design guide.
> >>>
> >>>
> >>>
> http://www.cisco.com/en/US/docs/solutions/Enterprise/Campus/HA_campus_DG/hacampusdg.html
> >>>
> >>>
> >>>
> >>> See the paragraph below. Why does the address space selected for the
> >>> distribution-to-distribution link must be within the address space
> being
> >>> summarized to be effective?
> >>>
> >>>
> >>>
> >>> "Because the distribution nodes send summarized information towards the
> >>> core, an individual distribution node does not advertise loss of
> >>> connectivity to a single VLAN or subnet. This means that the core does
> not
> >>> know that it cannot send traffic to the distribution member where the
> link
> >>> has failed. Adding an L3 link between the distribution switches allows
> the
> >>> distribution node that loses connectivity to a given VLAN or subnet to
> >>> reroute traffic across the distribution-to-distribution link. The
> address
> >>> space selected for the distribution-to-distribution link must be within
> >>> the
> >>> address space being summarized to be effective."
> >>>
> >>>
> >>> Blogs and organic groups at http://www.ccie.net
> >>>
> >>> _______________________________________________________________________
> >>> Subscription information may be found at:
> >>> http://www.groupstudy.com/list/CCIELab.html
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>
> >>
> >> --
> >> Pavel Bykov
> >> ----------------
> >> Don't forget to help stopping the braindumps, use of which reduces value
> of
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> http://www.stopbraindumps.com/
> >
> >
> > Blogs and organic groups at http://www.ccie.net
> >
> > _______________________________________________________________________
> > Subscription information may be found at:
> > http://www.groupstudy.com/list/CCIELab.html
> >
> >
> >
> >
> >
> >
> >
> >
>
>
>
> --
> Ronald Angello
> CCIE #17846
>
-- Pavel Bykov ---------------- Don't forget to help stopping the braindumps, use of which reduces value of your certifications. Sign the petition at http://www.stopbraindumps.com/Blogs and organic groups at http://www.ccie.net
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