Re: BGP Case Studies

No split horizon wont take that into consideration. It will only
prevent you from sending the route back on the same interface in the
same protocol. You can learn the route from eigrp, redsitribute it
into bgp, and then advertise it back to the original source. You just
can't advertise it back in eigrp.

-Marc

On Sat, Sep 17, 2011 at 12:47 AM, Kirk Douglas <krkdgls5_at_gmail.com> wrote:
> I was reading the BGP Case Studies on Cisco's site at this link:
>
> http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800c95bb.shtml
>
> It states:
>
> The network command is one way to advertise your networks via BGP. Another
> way is to redistribute your IGP into BGP. Your IGP can be IGRP, Open
> Shortest Path First (OSPF) protocol, RIP, Enhanced Interior Gateway Routing
> Protocol (EIGRP), or another protocol. This redistribution can seem scary
> because now you dump all your internal routes into BGP; some of these routes
> can have been learned via BGP and you do not need to send them out again.
> Apply careful filtering to make sure that you send to the Internet-only
> routes that you want to advertise and not to all the routes that you have.
> Here is an example:
>
> RTA announces 129.213.1.0 and RTC announces 175.220.0.0. Look at the RTC
> configuration:
>
> If you issue the network command, you have:
>
> RTC#
> router eigrp 10
> network 175.220.0.0
> redistribute bgp 200
> default-metric 1000 100 250 100 1500
>
> router bgp 200
> neighbor 1.1.1.1 remote-as 300
> network 175.220.0.0 mask 255.255.0.0
>
> !--- This limits the networks that your AS originates to 175.220.0.0.
>
> If you use redistribution instead, you have:
>
> RTC#
> router eigrp 10
> network 175.220.0.0
> redistribute bgp 200
> default-metric 1000 100 250 100 1500
>
> router bgp 200
> neighbor 1.1.1.1 remote-as 300
> redistribute eigrp 10
>
> !--- EIGRP injects 129.213.1.0 again into BGP.
>
>
> If you take a look at diagram in the link for this secition you will get a
> better understanding of my question. Read from the part where it states "*This
> redistribution can seem scary because now you dump all your internal routes
> into BGP; some of these routes can have been learned via BGP and you do not
> need to send them out again*" after looking at the diagram. It also states "
> *EIGRP injects 129.213.1.0 again into BGP*" at the end. This seems wrong to
> me but please let me know if I am mistaken. My question is about the ""*EIGRP
> injects 129.213.1.0 again into BGP*". From my understanding about split
> horizon, if eigrp 10 is redistributing bgp routes to the neighbor then the
> neighbor wouldn't advertise those routes back to RTC where it is
> redistributing eigrp 10 into bgp 200. If so, then how can EIGRP inject
> 129.213.1.0 back into BGP? Am I correct in my assumption here?
>
>
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Received on Sat Sep 17 2011 - 08:06:11 ART