BGP Case Studies

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 - 01:47:59 ART