From: Michael Wong (Michael.Wong@xxxxxxxxxx)
Date: Sat Sep 01 2001 - 00:04:08 GMT-3
OK, lets start with the "network" only command. On page 238, Doyle's book state
s .....
".... the network command causes the EBGP discovered routes to be treated as lo
cal BGP routes. Network 172.17.0.0 is advertised to Lillehammer via EBGP, for i
nstance, 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 rout
e 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 ha
s 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 stat
es ....
"The network backdoor command has the same effect as the network command. The E
BGP route is treated as a local BGP route, and the AD is changed to 200. The di
fference is that the address specified by the network backdoor command is not a
dvertised to EBGP peers."
OK, so basically I understand this to be the RIP route will take over as it sti
ll 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 ad
vertised etc., but it seems that when the "backdoor" command is used, the route
s 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
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