From: Narbik Kocharians (narbikk@gmail.com)
Date: Thu Jul 06 2006 - 05:59:02 ART
*Note if R1 router is receiving routing information for network
150.1.2.0/24 from two different sources, let's say EBGP and Eigrp and
Eigrp was
offering a more attractive path to Network 150.1.2.0 /24, R1 will accept the
routing information from EBGP, because it has a lower administrative
distance (20 versus 90). The "Network backdoor" command is BGP's solution to
this situation, BGP's "backdoor" command assigns an administrative distance
of 200 to the Eigrp network that its advertising, in this case 150.1.2.0/24.
*
*After entering the "backdoor" command, the router will accept Eigrp's
advertisement, because Eigrp will have a lower administrative distance (90
versus 200). *
*Understand that this router is not the originator of network 150.1.2.0 /24,
but it has to use the "network" command in order to apply the "backdoor"
keyword to network 150.1.2.0 /24. *
*A "show ip route" command will reveal that Eigrp is the path that this
router takes to get to network 150.1.2.0 /24. *
R1(config)#router bgp 200
R1(config-router)#network 150.1.2.0 mask 255.255.255.0 backdoor
Narbik Kocharians
CCIE# 12410 (R&S, SP, Security)
CCSI# 30832
Network Learning, Inc. (CCIE class Instructor)
www.ccbootcamp.com (CCIE Training)
On 7/6/06, Mister T <romantic24hrs@gmail.com> wrote:
>
> Hi...I took this from McGraw Hill book (I already practiced it), saying :
>
> Cisco provides a way to force IGP routes to take precedence over EBGP
> routes. The concept is called
> "backdoor links." EBGP routes can be tagged as backdoor routes, which sets
> the distance of these routes to the
> same as BGP local or 200. Since the distance is then higher than the IGP
> route, the backdoor IGP route is preffered.
>
> In order to get Router to prefer the IGP learned route, the BGP learned
> prefix must be tagged as a backdoor route. To tag the network prefix as a
> backdoor route perform the following on Router:
> Router(config)#router bgp 300
> Router(config−router)#network 152.1.1.4 mask 255.255.255.252backdoor
>
> mister t
>
> On 7/6/06, mattclark@hispeed.ch <mattclark@hispeed.ch> wrote:
> >
> > Hi group
> >
> > Came across this command and wanted to know a useful example of when to
> > implement this feature. is a backdoor route just a fancy way of saying a
> > backup route if you lost routes? the DocCD states that a backdoor
> network is
> > treated as a local network, except that it is not advertised.
> > Any other explanations would be appreciated.
> >
> > Matt
> >
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