From: Darren Ward (dward@xxxxxxxxxx)
Date: Mon Sep 03 2001 - 05:54:16 GMT-3
Absolutely correct, it listens for an EBGP advert for that network and AD's it
to 200. It will not create one from the IGP learnt route.
Darren
afiddler wrote:
> (If you are saying what I think you are saying), Halabi indicates the
> following in his example on pag 327 of the second edition:
>
> "Note that the network 192.168.10.0 backdoor will not cause BGP to generate
> an advertisement for that network."
> ----- Original Message -----
> From: "Darren Ward" <dward@pla.net.au>
> To: "Michael Wong" <Michael.Wong@nec.com.au>
> Cc: "'afiddler'" <afiddler@wi.rr.com>; "Peng Li" <lipeng@canada.com>;
> "Groupstudy - CCIELAB (E-mail)" <ccielab@groupstudy.com>
> Sent: Sunday, September 02, 2001 10:51 AM
> Subject: Re: BGP Backdoor (Doyle Vol II page 240)
>
> > Hi Peng,
> >
> > As far as I see the backdoor command you are telling the router that if it
> hears that route from an EBGP Neighbor pop it in the table with an admin
> distance of 200 that way IF there is an IGP known route it will be preferred
> over the EBGP route that know has the AD 200. (Also as you said it will not
> pass on the route as Internal)
> >
> > Otherwise you learn it as an AD 20 which over rules any IGP's normal AD.
> >
> > By not originating the route it means that it will not advertise the local
> IGP route via BGP because the 'backdoor' parameter was attached, without the
> backdoor parameter it's a plain old BGP network statement and since the
> route is known via an IGP it would announce it of course.
> >
> > I think it will still advertise the neighbor announced route with it's AS
> in the path as per normal it just will not originate one of its own.
> >
> > Anyone correct the last statement I haven't had time to test it yet?
> >
> > Darren
> >
> > Michael Wong wrote:
> >
> > > OK, lets start with the "network" only command. On page 238, Doyle's
> book states .....
> > >
> > > ".... the network command causes the EBGP discovered routes to be
> treated as local BGP routes. Network 172.17.0.0 is advertised to Lillehammer
> via EBGP, for instance, and is entered into the routing table. The command
> network 172.17.0.0 is added to Lillehammer's configuration, even though
> 172.17.0.0 is not really a local route. Because the address is in the
> routing table, the network command matches it and makes it a local route."
> > >
> > > ".... By first being an EBGP route, 172.17.0.0 is changed into a local
> BGP route with the network command. Because 172.17.0.0 is now considered a
> local route at Lillehammer, it is assigned an AD of 200. The RIP route to
> 172.17.0.0 now has a lower AD and becomes the preferred route ...."
> > >
> > > The above makes perfect sense and I can get this part to work .... yes
> it does take a little time for it to appear, but other than that, no
> problems. However my issue is with the "network backdoor" command. On page
> 241, Doyle's book states ....
> > >
> > > "The network backdoor command has the same effect as the network
> command. The EBGP route is treated as a local BGP route, and the AD is
> changed to 200. The difference is that the address specified by the network
> backdoor command is not advertised to EBGP peers."
> > >
> > > OK, so basically I understand this to be the RIP route will take over as
> it still has the lower AD, however the only difference is that the address
> specified in the network command will not be advertised ..... cool !!!! No
> problems ...... I get the picture and the logic about why you don't want the
> network to be advertised etc., but it seems that when the "backdoor" command
> is used, the routes no longer become local ???? By the way they also don't
> get advertised.
> > >
> > > Am I understanding this correctly and I'm having these issues due to
> dodgy IOS ????
> > >
> > > Thanks .... MW :)
> > >
> > > -----Original Message-----
> > > From: afiddler [mailto:afiddler@wi.rr.com]
> > > Sent: Saturday, 1 September 2001 9:02 am
> > > To: Peng Li; Michael Wong
> > > Subject: Re: BGP Backdoor (Doyle Vol II page 240)
> > >
> > > My study buddy and I went through this lab just a few weeks ago. It
> seems
> > > to work as stated. Lillehammer does not really have the RIP route, but
> > > advertises it so that it looks like an IBGP route. With a much higher
> AD,
> > > this route is not preferred as long as the RIP route exists. As soon as
> the
> > > RIP route disappears, the next best route is the IBGP route from
> > > Lillehammer, which advertises it with an origin of IGP.
> > >
> > > Perhaps I just do not understand the issue you are having. I would be
> happy
> > > to set this up again in my lab and provide some results to you if that
> would
> > > help.
> > > ----- Original Message -----
> > > From: "Peng Li" <lipeng@canada.com>
> > > To: "Michael Wong" <Michael.Wong@nec.com.au>; <ccielab@groupstudy.com>
> > > Sent: Friday, August 31, 2001 6:03 AM
> > > Subject: Re: BGP Backdoor (Doyle Vol II page 240)
> > >
> > > > Hi,
> > > > I think there's several examples in the book either Jeff overlooked or
> > > doesn't elaborate in much detail or maybe some misunderstanding If I
> dare to
> > > challenge.
> > > >
> > > > One of the AM example is what you discovered. According to my
> > > understanding and lab results, the "network xxx backdoor" does't change
> the
> > > Ebgp into IBGP with changing AD from 20-200. This is not the way it
> works.
> > > When you finish you config of AM command, you should shut down the EBGP
> > > neibor and see the difference. It works now. The reason is that it takes
> > > time for EBGP tcp connection to setup and get routes with AD20,
> > > approximately 40-50 seconds. By this time, the rip already got the route
> and
> > > by using "network" command . The rip learned route is already entered in
> > > Local BGP table with Weitht 32768 much hiher than the later learned EBGP
> > > with Weight of 100, this cause the Router deny EBGP routes and prefer
> IBGP
> > > one. at the same time, he keeps the RIP one in RT.
> > > >
> > > > Hope it helps and correct me if I'm wrong.
> > > >
> > > > Take care.
> > > > My lab is Oct.10 in Beijing.
> > > >
> > > > ----- Original Message -----
> > > > From: "Michael Wong" <Michael.Wong@nec.com.au>
> > > > To: "Groupstudy - CCIELAB (E-mail)" <>
> > > > Sent: Friday, August 31, 2001 1:40 AM
> > > > Subject: BGP Backdoor (Doyle Vol II page 240)
> > > >
> > > >
> > > > > BGP gurus .....
> > > > >
> > > > > Has anyone managed to get BGP backdoor to work properly ??? I'm
> going
> > > through Doyle's example on page 240 and I can't seem to get the BGP
> backdoor
> > > command to work properly.
> > > > >
> > > > > The funny thing is that I am able to get the correct results and
> change
> > > the EBGP route to a local BGP route and make RIP take precedence over
> the
> > > local BGP route with the "network 172.18.0.0" command, however when I
> use
> > > the same network command and just add "backdoor" to it, the RIP routes
> do
> > > not appear .... strange I thought ????
> > > > >
> > > > > The RIP routes are definitely getting through as when I close the
> BGP
> > > sessions, the RIP routes appear in the routing table. It seems that when
> the
> > > "backdoor" command is added to the network command, BGP does not modify
> the
> > > EBGP to a local BGP route and the route table still has an AD of 20.
> > > > >
> > > > > Any thoughts ????
> > > > >
> > > > > Thanks peoples ..... MW
> > > > > **Please read:http://www.groupstudy.com/list/posting.html
> > > > **Please read:http://www.groupstudy.com/list/posting.html
> > > **Please read:http://www.groupstudy.com/list/posting.html
**Please read:http://www.groupstudy.com/list/posting.html
This archive was generated by hypermail 2.1.4 : Thu Jun 13 2002 - 10:32:14 GMT-3