Lab Tip: Review What You’ve Typed Before Blaming IOS

I was trying to apply an IPv6 address to an interface and have it use EUI-64.  For some reason I was not able to get the ‘eui-64′ option to show up.

I immediately assumed that this was a Dynamips error:

Rack1R4(config-if)#ipv add 2001:CC1E:x:404::/64 ?
X:X:X:X::X/<0-128>  IPv6 prefix

Rack1R4(config-if)#ipv add 2001:CC1E:x:404:: ?
X:X:X:X::X/<0-128>  IPv6 prefix

Rack1R4(config-if)#ipv add 2001:CC1E:x:404::/64 ?
X:X:X:X::X/<0-128>  IPv6 prefix

Rack1R4(config-if)#ipv add 2001:CC1E:x:404::/64
% Incomplete command.

DOH!!!!  That ‘x’ was supposed to be a ’1′ (x is a variable that you’re supposed to fill in with your rack number).  I was a bit too literal in my task interpretation.    This was a PEBKAC error and not a Dynamips issue.

But ‘x’ is not a hexadecimal character (0 – 9 and A – F) so why didn’t IOS throw an error?

Rack1R4(config-if)#ipv6 address ?
WORD                General prefix name
X:X:X:X::X          IPv6 link-local address
X:X:X:X::X/<0-128>  IPv6 prefix
autoconfig          Obtain address using autoconfiguration

Ah. IOS thought that I had configured the “general prefix name” and was expecting the address to follow.

I typed the address correctly and all was well:

Rack1R4(config-if)#ipv6 address 2001:CC1E:1:404::/64 eui-6