CCIE Pursuit Blog

March 11, 2009

Core Knowledge Question of the Day: 11 March 2009

R1#ping FE80::2
Output Interface: Serial1/0
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to FE80::2, timeout is 2 seconds:
Packet sent with a source address of FE80::5
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/8/12 ms

Why must you specify an output interface when pinging FE80::2?

Highlight for answer: FE80::2 is an IPv6 link-local address.  IPv6 link-local address do not need to be unique on a router, but must be unique on an interface.  Because the same IPv6 link-local address can be present on multiple interfaces on a device, IOS needs to know the output interface.

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