Hi,
thinking about possible solution for this task I didn't consider the possibility to redistribut OSPF prefixes into RIP domain (which is done in 10.3) because it somehow contravers the task 3.3, but if you just configure the aggregate-address under R4 and not distribute the OSPF into RIP, then R4 losts the connection to OSPF domain , because aggragated prefix 139.1.0.0/16 is installed in routing table pointing to Null and that prefix "wins" over 0.0.0.0/0 which is generate by R5.
What I did is activated "auto-summary" under BGP process on R4 and R6 and just announce additionaly 139.1.5.0/24 on R4 via network statement:
R4:
router bgp 100
synchronization
bgp log-neighbor-changes
network 139.1.0.0
network 139.1.5.0 mask 255.255.255.0
neighbor 150.1.6.6 remote-as 100
neighbor 150.1.6.6 update-source Loopback0
neighbor 150.1.6.6 next-hop-self
neighbor 204.12.1.254 remote-as 54
neighbor 204.12.1.254 route-map R4-BB3 in
neighbor 204.12.1.254 maximum-prefix 150000 90
auto-summary
R6:
router bgp 100
synchronization
bgp log-neighbor-changes
network 139.1.0.0
neighbor 54.1.2.254 remote-as 54
neighbor 54.1.2.254 route-map R6-BB1 in
neighbor 54.1.2.254 maximum-prefix 150000 90
neighbor 150.1.4.4 remote-as 100
neighbor 150.1.4.4 update-source Loopback0
neighbor 150.1.4.4 next-hop-self
auto-summary
auto-summary under BGP works quite interesting:
"network—For network commands that list a classful network number and no mask
parameter, inject the classful network if at least one subnet of that classful network exists in
the IP routing table."
and at the same time the classless prefix can be advetised with help of other network statement.
what we get is advertising 139.1.0.0/16 and 139.1.5.0/24 from R4 and only 139.1.0.0/16 from R6
Rack1R4#sh ip bgp neigh 204.12.1.254 adv
BGP table version is 7, local router ID is 150.1.4.4
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 139.1.0.0 0.0.0.0 0 32768 i
*> 139.1.5.0/24 0.0.0.0 1 32768 i
Total number of prefixes 2
Rack1R6(config)#do sh ip bgp neig 54.1.2.254 adv
BGP table version is 28, local router ID is 150.1.6.6
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 139.1.0.0 0.0.0.0 0 32768 i
Total number of prefixes 1
Any comments are welcome, I don't see why this solution would be not accepted.