From: Josef A (josefnet@gmail.com)
Date: Tue Jan 09 2007 - 01:26:46 ART
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
This archive was generated by hypermail 2.1.4 : Thu Feb 08 2007 - 23:46:56 ART