Showing results for 
Search instead for 
Did you mean: 

query about IPv6 address


                   Dear All,

can i use this ip address as private ip address

L0: 2001:192:168:100::1/128

and the point to point ipv4 address is: can i use 2001: 192:168:1::1/126

because i am using IPv4 address

if not what must i use it to acheive my setup


4 Replies 4

James Leinweber

That would be a bad idea, as 2001::/16 is already allocated by IANA and is globally routed.   It won't be a prefix your ISP is willing to route for you, and if it escapes, probably someone else is already using it.

If you want a non-routable private v6 address, you have two main choices:

(1) for Link-local use only, you can use your automatically configured lihk-scope fe80::/64 address. 

Typically the host part (bottom 64 bits) will use the EUI-64 mapping off your ethernet MAC, which is, insert fffe in the middle and flip the global/local flag bit.

(2) For site-scope, use RFC-4192 unique local  addresses, which are the v6 replacement for RFC-1918 v6 private addresses.  They will look like fd+40 random bits as a /48 prefix, then you allocate the bottom 80 bits as your usual 16 bits of subnetting and  64 bits of host part.

If you want a non-routable documentation address, the v6 range for published examples is 2001:db8::/32.

People who want to embed v4 bits into v6 addresses usually put them at the bottom of the host part, so you could use whatever prefix you end up with and host part ::  (0000:0000:c0a8:6401).

-- Jim Leinweber, WI State Lab of Hygiene


You can use as private but you cant use it as can use unique local addresses with startin fc0:: space

Sent from Cisco Technical Support Android App

Dear All,

Can you tell me what is the IPv6 subnet can use it for enterprise inteast of the IPv4?

for example

IPv4 --- loopback: what is the equivelent for ipV6

IPv6 p2p ---- what is the equivelent for IPv6

thanks in advanced

Some address classes compared between IPv4 and IPv6

loopback:  v4,  v6 ::1/128

link-local zeroconf:   v4,  v6 fe80::/64

private, site-scope, not globally routeable:

   v4: rfc-1918,,,

   v6: rfc-4192: fdxx:yyyy:zzzz::/48, where xx:yyyy:zzzz are local chosen once, psuedo-randomly

multicast:      v4:      v6: ff00::/8

If you have a router which is using as its gateway address and a tunnel which is using as a transit subnet for  point to point link, the questions are:

   * does the router support IPv6?  If so, it should be sending ICMPv6 router advertisements (message type 134), which will exhibit the link-local address of the gateway (fe80::....) as the IPv6 sender.

   * does the tunnel support IPv6?  If so, it will probably be configured with an IPv6 transit subnet either /46 or /127 in size, probably using a putatively globally routable prefix starting with 2::/3.   What you should use locally depends on what the remote end is willing to offer.

If you could provide more details about the network topology and devices and ISP, we might be able to offer more specific advice.

-- Jim Leinweber, WI State Lab of Hygiene

Getting Started

Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community:

Recognize Your Peers