This solution uses a key chain named CCIE and key strings named exercise2a and exercise2b. Assuming today's date is November 30, 2004, and the first key begins being used at 8:30 AM, the configurations of the serial interfaces are
key chain CCIEkey 1key-string exercise2aaccept-lifetime 08:30:00 Dec 2 2004 08:30:00 Jan 1 2005send-lifetime 08:30:00 Dec 2 2004 08:30:00 Jan 1 2005key 2key-string exercise2baccept-lifetime 08:30:00 Jan 1 2005 infinitesend-lifetime 08:30:00 Jan 1 2005 infinite!interface Serial0ip address 172.16.3.19X 255.255.255.252ip authentication key-chain eigrp 5 CCIEip authentication mode eigrp 5 md5
The statement ip summary-address eigrp 5 172.18.10.192 255.255.255.224 is added to RTA's interface on subnet 172.18.10.96/27. Also, note that auto-summarization must be turned off on RTA, because of the appearance of the 172.16.0.0 network on RTF.
5
RTA can send a summary address of 172.16.3.128/25 to RTF and a summary address of 172.16.3.0/25 to RTB. All other summarization is performed automatically.