7.47 AS300 still transiting traffic between AS200 and AS100

Part of this task is prevent AS300 transiting traffict to/from AS200 and AS100. 

However AS300 is inadvertently used for transit as the the next hop 155.x.45.4 recurses to R3 f0/0 with a next hop of 155.x.67.7!

See below using a example prefix -

Rack15R3#show bgp ipv4 unicast 28.119.16.0
BGP routing table entry for 28.119.16.0/24, version 7
Paths: (2 available, best #1, table Default-IP-Routing-Table)
  Advertised to update-groups:
        1    2    4    5
  100 54
    155.15.45.4 (metric 27262976) from 155.15.0.5 (150.15.5.5)
      Origin IGP, metric 0, localpref 150, valid, internal, best
  100 54
    155.15.13.1 from 155.15.13.1 (150.15.1.1)
      Origin IGP, localpref 100, valid, external
Rack15R3#

Looking at CEF we have -

Rack15R3#show ip cef 28.119.16.0/24 detail
28.119.16.0/24, epoch 0
  recursive via 155.15.45.4
    nexthop 155.15.37.7 FastEthernet0/0

Which is of course the next hop into AS300 on SW1!

As you can see traffic successfully follows this path WRT R3 -

Tracing the route to 28.119.16.1

  1 155.15.37.7 [AS 100] 4 msec 4 msec 0 msec
  2 155.15.67.6 [AS 100] 4 msec 0 msec 0 msec
  3 54.15.1.254 28 msec 32 msec 28 msec
  4 172.16.4.3 8 msec *  8 msec

Clearly this is not a problem with the BGP config but the underlying IGP which is EIGRP.

Increasing the delay on interface f0/0 or using next-hop self on R5 would resolve the problem I chose the former solution

Rack15R3(config)# int f0/0
Rack15R3(config-if)#delay 20000
Rack15R3(config-if)#

We now get -

Rack15R3#show ip cef 28.119.16.0/24 detail
28.119.16.0/24, epoch 0
  recursive via 155.15.45.4
    nexthop 155.15.0.5 Serial0/0/0.1

And the correct result -

Rack15R3#traceroute 28.119.16.1

Type escape sequence to abort.
Tracing the route to 28.119.16.1

  1 155.15.0.5 [AS 100] 28 msec 28 msec 28 msec
  2 155.15.45.4 [AS 100] 16 msec 16 msec 16 msec
  3 155.15.146.6 [AS 100] 16 msec 16 msec 16 msec
  4 54.15.1.254 44 msec 44 msec 44 msec
  5 172.16.4.3 24 msec *  24 msec

Although not a problem for this task in volume 1 technically with the either of the above changes AS300 is used for transit for prefixes originating in AS54 with traffic via R5 and then R4.