terface. Now let's make our little network a tad more interesting. I'll add a third router, R4, hanging off of F0/1 on R1. It will look like Figure 37-2. :1::/64 :101::/64 AAAA :AAAA:AAAA: : /48 Figure 37-2. A three-router IPV6 network First, the f0/1 interface on R1. This is the same prefix, but with a subnet of : 101: interface FastEtherneto/1 ipv6 address AAAA: AAAA: AAAA: 101: : 1/64 And now, on R4, I'll add the host address of : :4 on the same prefix and subnet: (config)#int fo/1 (config-if)#ipv6 address aaaa:aaaa:aaaa:101::4/64 Another quick ping, and we're in business: R4#ping ipv6 aaaa:aaaa:aaaa:101::1 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to AAAA:AAAA:AAAA:101::1, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 0/146/728 ms But we can't ping the other subnet's router interface on R1: R4#ping ipv6 aaaa:aaaa:aaaa:1::1 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to AAAA:AAAA:AAAA:1::1, timeout is 2 seconds: Success rate is 0 percent (0/5) Why not? Shouldn't R1 forward packets for connected interfaces? Not by default in IPv6. With IPv6 on a Cisco device, you must enable IPv6 unicast-forwarding: R1 (config)#ipv6 unicast-routing Once I've done this, I can ping through the R1 router to its other interface: R4#ping ipv6 aaaa:aaaa:aaaa:1::1 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to AAAA:AAAA:AAAA 1::1, timeout is 2 seconds: Chapter 37: IPv6 Success rate is 100 percent (5/5), round-trip min/avg/max = 0/0/4 ms But check this out-I can also ping the f0/0 interface on R6: R4#ping ipv6 aaaa:aaaa:aaaa:1::6 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to AAAA:AAAA:AAAA:1::6 timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 0/0/4 ms There is no routing configured on R1. R1 will route locally connected interfaces by default, but we haven't configured any default gateways or static routes on either R6 or R4. What gives? Remember those router advertisements I talked 