overlapping address in ipv6 but no error message

[sarahr202]

Hi everybody.

please consider the following address- overlapping- scenario:

R2(config)#int loopback 2

R2(config-if)#ipv6 address 2002:a09:901:1::1/64

R2(config-if)#int tunnel 1

R2(config-if)#ipv6 address 2002:a09:901::/128

I don't get any error even though we have overlapping address. For example,  the range of valid ipv6 address on subnet 2002:a09:901::/64 is 

2002:a09:901:: ----  2002:a09:901:FFFF:FFFF:FFFF:FFFF:FFFF

The address 2002:a09:901:: configured on tunnel interface falls with in the range described above but yet we don't get any error message.

If I perform the similar action on ipv4 enabled interface, I will get error.

R2(config)#int loopback 4

R2(config-if)#ip address 12.12.12.12 255.255.0.0

R2(config-if)#int loopback 13

R2(config-if)#ip address 12.12.12.12 255.255.255.0

% 12.12.12.0 overlaps with Loopback4

In above case we get error because address 12.12.12.12/24 falls  in the range of subnet 12.12.0.0/16.  However  in case of ipv6,  the address 2002:a09:901::/128 on tunnel1 falls with in range of prefix 2002:a09:901::/64,but yet we don't get any error message.

Any input will be greatly appreciated.

[stmillet · Accepted solution]

If the example you provided is as you typed it in the IOS CLI then these are not overlapping IPv6 ranges

The range on loopback2 in it's expanded format is:

2002:0a09:0901:0001::1/64

The range on tunnel 1 is

2002:0a09:0901:0000::/128

These are different /64s (/64 boundary is after the 4th Hextet, not after the embedded IPv4 address which is a /48)

I hope this clarifies the issue.

[sarahr202]

HI stmillet.

I am still at loss.

I am going to break it down for better understanding for myself

int loopback2

2002:0a09:0901:0001::1/64

Range will be   2002:0a09:0901:1:0:0:0:0------2002:0a09:0901: 1:ffff:fffff:ffff:ffff

is that the correct range?

int tunnel

2002:0a09:0901:0000::/128

First , I need to clarify what prefix length  are you referring to  is  48/ or 128?

Let say it is 48 .i.e  2002:0a09:0901::/48

then range will be:    2002:0a09:0901:0:0:0:0:0----- 2002:0a09:0901:ffff:ffff:ffff:ffff:ffff

the adress assigend to loopback2 i.e 2002:0a09:0901:1::1 falls in the above range. Is that correct ?

thanks and I appreciate your help.

[stmillet · Accepted solution]

Hopefully this will help:

  int loopback2

  2002:0a09:0901:0001::1/64

  Range will be   2002:0a09:0901:1:0:0:0:0------2002:0a09:0901: 1:ffff:fffff:ffff:ffff

Correct

  int tunnel

  2002:0a09:0901:0000::/128

This address with any mask from /64 - /128 will _not_ overlap with the above subnet of loopback 2

If the mask is any smaller then /64 (

My point about the /48 vs /64 was just a point of clarification to ensure you were not assuming that the /64 bit boundary wasn't somewhere where it wasn't. For all intents and purposes ignore this if it is confusing and just focus on the above.

I hope this helps

[sarahr202]

Thanks Stmillet. I apologies for the late reply.