>Hi,there:
>
>I'm studying the section of <neighbor doorback> in Halabi's book,
>But unfortunately, I never get pass.
>
>Please watch the topology attached in this mail, The 3640-1,2610,
>2501-2 router run bgp protocol,but ospf run between 3640-1 and
>3640-2.
>
>
>The question is if I use clear ip bgp * command, the ospf route
>192.68.5.0 255.255.255.0 192.68.6.2 will appear in 3640-1's routing
>table,but after BGP peer established,this route was replaced with
>BGP route 192.68.5.0 255.255.255.0 172.16.20.2.
>
>I know the reason is the distance,but the fact is I have set the
><network 192.68.5.0 backdoor> command in 3640-1!
>the BGP route 192.68.5.0 255.255.255.0 172.16.20.2's distance should
>change from 20 to 200 and that ospf's route should stay in 3640-1's
>routing table,it cann't be replaced by BGP's route again! SO,I cann't
>understand completely.
Again, don't worry too much about the more obscure commands at first,
concentrate on understanding what happens, and then study one
additional command at a time. Before adding additional commands,
have a clear idea:
what is your routing policy?
how do you want the added command to change the routing policy?
Halabi (1st ed -- I have 2nd ed on order) doesn't present things in
this manner, I agree. But in many respects, his Parts 3 and 4 should
be studied before Part 2. Learn policy before configuration.
So what are you trying to do with the backdoor command? I say this,
in part, because I've never found a real-world case where I needed
it. There are some examples in documentation, I will admit.
Looking at the Halabi examples, I think it's cleaner to use a
route-map to redistribute the IGP route into BGP, setting a
local-preference to make it preferred. Local preference is BGP
standard, while backdoor is not.
>
>Another question:
>When I use <clear ip bgp *> command, then <sh ip route ospf>, I can
>find the route 192.68.5.0 255.255.255.0 192.68.6.2 appeared,but the BGP
>esatblished,the route then disappeared from the output of the <sh ip
>route ospf>.
>What's happen ?
Without further information, I would think that the potential route
announced by BGP is being preferred, so the native OSPF route is
being suppressed.
>
>
>Thank in advance...
>
>
> Zhang Hui
> [EMAIL PROTECTED]
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