From: Alan Simpkins (alan_simpkins@xxxxxxxxx)
Date: Mon Jul 31 2000 - 14:43:27 GMT-3
Hello All, my name is Alan Simpkins. I will be taking
my 4th swing at the lab at the end of Nov. I have
taken it in San Jose twice, and most recently at RTP
(Bad Idea). Here are a couple thoughts:
1. Don't wait too long between exams, I waited a yr
between 2nd, and 3rd.
2. Practice BGP as if No sync is not an option, it
probably will not be allowed.
Regards
Alan Simpkins
CCNP, CCDP, BNCHS, and NNCSS
--- pkm@calweb.com wrote:
> Based on my lab experiences with BGP, I do not think
> that fully IBGP
> speakers is a requirement. Let's say that al your
> router inside your
> transit AS are only BGP speakers and there is no IGP
> runnning. You will
> still have to use the NO SYNCH command on the IBGP
> speakers, regardless
> of having full IBGP mesh topology. If no synch is
> used, the network will
> not appear in the route table even if it in the BGP
> route table. There
> is a good example on the Cisco web site at :
> http://www.cisco.com/warp/public/459/14.html (BGP
> Case study Section 2):
> http://www.cisco.com/warp/public/459/14.html#A15.0.
> Also, the book All
> in oneCCIE lab study guide has good examples of the
> no synch rule.
> Also, for the CCIE lab, it is most likely that you
> will have to apply
> the next-hop-self statement to the transit AS. The
> combination of these
> two commands (next-hop-self and no synch) allows the
> BGP route table to
> show up in the IP route table of the IBGP speakers
> correctly. See all in
> one CCI Elab study guide. http://www.mentortlabs.com
> has a good lab
> demonstrated the issues with no synch and
> next-hop-self in a NBMA
> network.
>
> Sincerely,
>
> Phillip
>
>
>
> Geatti wrote:
>
> > Fred,The sync rule basically says in order to
> advertise a route it
> > needs to be in the RIB (Routing information base)
> and the routing
> > table. Turning sync off via the "no sync" command
> will allow you to
> > advertise a given route without it being learned
> via IGP first. Now
> > most people would say, why on earth would you want
> to redistribute all
> > the routes learned via EBGP into IGP, that would
> be crazy yeah? And
> > you would be right. Running no sync with IBGP
> routers is the way to
> > go.However to run no sync you must meet one of the
> following
> > criteria....a. you must be fully meshed IBGP
> within your AS. ORb.
> > you are a stub network - not transit. The reason
> for the sync rule is
> > to prevent a packet arriving into your AS
> destined for another AS
> > (meaning you are transit) getting to a router
> within your AS that does
> > not know what to do with it. If you are running
> sync with IGP this
> > would not matter as you would have a IGP route to
> the external
> > destination. If you are not in sync as soon as
> your packet hits the
> > router it won't know how to handle it, doesn't
> have an IGP route to
> > the destination nor is it running IBGP, it won't
> have a route to that
> > external AS, the packet is dropped.The sync rule
> says that IGP must be
> > synchronized with BGP routes, this is not
> practical in most cases.
> > Therefore make sure that when you use no sync on
> all routers within
> > you AS that you are fully meshed via IBGP or using
> something like
> > route reflectors to make appear so. If you are
> fully meshed via IBGP
> > there is no need to be sync.Sync does require you
> to have an exact
> > match I believe, 10.0.0.0 /8 does not catch
> 10.10.10.0 /24 and
> > 10.5.0.0 /16. An exact match is necessary.Hope
> this is of some
> > helpMarco-----Original Message-----
> > From: nobody@groupstudy.com
> [mailto:nobody@groupstudy.com]On Behalf Of
> > Fred Nielsen
> > Sent: Saturday, July 29, 2000 8:51 PM
> > To: ccielab@groupstudy.com
> > Subject: BGP Synchronization rule
> >
> >
> > I would like to hear the opinions of the
> group on the
> > synchronization rule, which states
> *something* like: a BGP
> > router will not forward an externally learned
> route to
> > another external peer until the route is also
> present in
> > that router's IGP as well. The Halabi book
> touches on this,
> > but didn't spend enough time for me to really
> understand the
> > intent behind the rule, other than to prevent
> routing loops
> > inside an AS. Because many typical
> configurations out there
> > do not redist BGP routes into IGP's, you see
> the "no
> > synchronization" command employed fairly
> often. Why is sync
> > turned on by default in the IOS? Is it part
> of the
> > specification perhaps? Also, referring to
> "external peer"
> > above, this really means separate router
> entities running
> > IBGP within an AS, right? Not between EBGP
> peers, where the
> > rule doesn't apply.. And one more question,
> does the IGP
> > route have to match precisely, or can a less
> specific route
> > do the trick? In other words, can the
> presence of
> > 10.0.0.0/8 in the IGP allow BGP to forward a
> 10.1.0.0/16
> > route? Hoping all this makes sense.------
> > Fred Nielsen [fred_nielsen@hotmail.com]
> > ------
> >
>
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