From: Carlos G Mendioroz (tron@xxxxxxxxxxx)
Date: Fri Jun 28 2002 - 13:20:28 GMT-3
Annu,
Annu Roopa wrote:
>
> Carlos,
>
> Some clarifications.
>
> With rgds to answer#1 of urs by BGP u mean EBGP ?? if
No, I mean BGP.
> its iBGP then once again synch issues will be
> there.Assume there is no IGP and i give 'no
> sychroniza' on R2 packets will get dropped when they
> go from R20 towards R10.To avoid it WE MUST HAVE
> ROUTES IN iP TABLE SO how do we get it on R2 or R3
> other than running some IGP.
Synch is ONLY an issue with iBGP. There's no such
thing as synch for eBGP learned routes.
When you set "router bgp xxx/no synch" you are telling the
router to IGNORE the synch requirement and do use
(and install) routes that you have in BGP table even though
you don't have them (beforehand) in your routing table.
By having no synch, you can actually use BGP as your IGP...
(not something I would do in general :-)
>
> With rgds #2 this is new info to me.Is there a doc
> with rgds this or URL. I know this has been discussed
> previously. Do u mean to say if R2 has iBGP with R1 as
> in diagram below the OSPF router id for a route must
> match the iBGP router id used on R2 for peering with
> R1 ?
Yes. And this is something that is implemented differently in
different IOS versions. Sadly, I've seen no document stating
HOW it is done. I hope Paul does get the search engine up and running
shortly. There are tons of info on this (an other) subjects
in the archives...
>
> Thanks for ur time and answers.
> Annu
>
> --- Carlos G Mendioroz <tron@huapi.ba.ar> wrote:
> > Annu Roopa wrote:
> > >
> > > Group,
> > >
> > > I understand why BGP synch is needed but have some
> > > clarifications.When we have scenario as below
> > >
> > > R10---------R1------R3-------R2---------R20
> > > Ebgp iBGP EBGP
> > >
> > > and R10 is in AS 100 and R1/R2/R3 in As200 and R20
> > in
> > > As300.In this scenario R2 will not advertise
> > routes
> > > learnt thru R10 to R20 without having the routes
> > in IP
> > > table right ??? The questions are:
> > >
> > > 1. Assuming there is no IGP on R1/R2/R3 what are
> > the
> > > options of having the routes in R2 in its IP
> > table.
> > > Should we should have static routes for all
> > networks ?
> > > Any other way.
> >
> > BGP/No synch :-)
> >
> > >
> > > 2. When BGP (say on R2) looks for synchronization
> > with
> > > an IGP what does it look for as a match?? - the
> > > network,mask and type (i mean IGP).They all should
> > > match in IP table to what is advertised by BGP
> > from
> > > R10.
> >
> > network/mask.
> > Iff IGP = OSPF, then also originating OSPF router-id
> > should
> > match iBGP neighbour router-id.
> >
> >
> > > The reason i ask this is there are times when i
> > have
> > > seen the route in IP table is /16 bit but /24 in
> > BGP
> > > table (without *>) and it does not work.Also when
> > the
> > > route is say OSPF E2 type is does not work.
> > >
> > > 3.If there is are multiple entries in BGP table
> > and i
> > > do a traceroute will the path taken be the (*>,
> > valid
> > > best path) or according to the IP table. I guess
> > *>
> > > path should match up with IP table path am i right
> > ?
> > > in understanding this.
> >
> > Packets will follow FIB (i.e. routing table) next
> > hop.
> >
> > >
> > > =====
> > > Thanks in advance for ur time and replies.
> > > Annu.
> > >
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