From: Narbik Kocharians (narbikk@gmail.com)
Date: Tue Jan 09 2007 - 05:27:14 ART
Good job ALI
On 1/8/07, Narbik Kocharians <narbikk@gmail.com> wrote:
>
>
>
> If you enter the network command with the backdoor option in an attempt to
> advertise a connected network, the local router will not advertise that
> network to any of it's BGP peers. But the reason we use the network command
> with the backdoor option is that we are receiving routing information
> from two sources (Routing Protocols) for a given network, an IGP and EBGP,
> and we like to prefer the IGP over the EBGP for the ADVERTISED network. In
> this situation the only thing that the "backdoor" option does is it
> increases the AD from 20 to 200. This can also be achieved by the distance
> command and the result is the same.
>
>
>
> On 1/8/07, Narbik Kocharians <narbikk@gmail.com> wrote:
> >
> > Josef,
> > When the network command is used with a backdoor option, it is
> > advertised to the ebgp peers. The reason for using the backdoor or the
> > distance option is because the network was advertised through an IGP and
> > BGP.
> >
> >
> > On 1/8/07, Josef A <josefnet@gmail.com> wrote:
> > >
> > > One notable difference as stated in the quote from the documentation
> > > is that
> > > a network configured with the backdoor command is not advertised to
> > > ebgp
> > > peers, thus if you just manually alter the distance, the network will
> > > be
> > > advertised. Since the bgp bestpath selection is not changed when a
> > > network
> > > is configured as backdoor you could actually have routing
> > > inconsistencies
> > > downstream moreso that the administrative distance is locally
> > > significant.
> > >
> > > HTH
> > > Josef
> > >
> > >
> > >
> > >
> > >
> > >
> > > On 1/8/07, Yasmin Lara < ylara@sunsetlearning.com > wrote:
> > > >
> > > > What's the difference between assigning an administrative distance
> > > of 200
> > > > for
> > > > a specific route and using the backdoor feature?
> > > >
> > > > For example:
> > > >
> > > > router bgp 300
> > > >
> > > > distance 200 192.168.100.1 0.0.0.0 99
> > > >
> > > > !
> > > >
> > > > access-list 99 permit 44.4.4.0 0.0.0.255
> > > >
> > > >
> > > >
> > > > vs.
> > > >
> > > >
> > > >
> > > > router bgp 300
> > > >
> > > > network 44.4.4.0 mask 255.255.255.0 backdoor?
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > According to the documentation: "A backdoor network is assigned an
> > > > administrative distance of 200. The objective is to make Interior
> > > Gateway
> > > > Protocol (IGP) learned routes preferred. A backdoor network is
> > > treated as
> > > > a
> > > > local network, except that it is not advertised. A network that is
> > > marked
> > > > as a
> > > > back door is not sourced by the local router, but should be learned
> > > from
> > > > external neighbors. The BGP best path selection algorithm does not
> > > change
> > > > when
> > > > a network is configured as a back door." "Changing the default
> > > > administrative distances is not recommended because changing the
> > > > administrative distance may lead to routing loops."
> > > >
> > > >
> > > >
> > > > I don't understand why changing the distance may lead to routing
> > > loops and
> > > > I
> > > > don't understand what difference is makes to set the distance for
> > > the
> > > > route as
> > > > 200 with the distance command or with the backdoor command. Am I
> > > missing
> > > > something?
> > > >
> > > >
> > > >
> > > > Thx!!!
> > > >
> > > >
> > > >
> > > > Yasmin.
> > > >
> > > >
> > > _______________________________________________________________________
> > > > Subscription information may be found at:
> > > > http://www.groupstudy.com/list/CCIELab.html
> > >
> > > _______________________________________________________________________
> > >
> > > Subscription information may be found at:
> > > http://www.groupstudy.com/list/CCIELab.html
> > >
> >
> >
> >
> > --
> > Narbik Kocharians
> > CCIE# 12410 (R&S, SP, Security)
> > CCSI# 30832
> > Network Learning, Inc. (CCIE class Instructor)
> > www.ccbootcamp.com (CCIE Training)
> >
>
>
>
> --
> Narbik Kocharians
> CCIE# 12410 (R&S, SP, Security)
> CCSI# 30832
> Network Learning, Inc. (CCIE class Instructor)
> www.ccbootcamp.com (CCIE Training)
>
-- Narbik Kocharians CCIE# 12410 (R&S, SP, Security) CCSI# 30832 Network Learning, Inc. (CCIE class Instructor) www.ccbootcamp.com (CCIE Training)
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