ipv6 address format

hi sorry about my first post being a question, im really stuck and could do with some help. ive checked many other places yet im still at a lost.

my question is
why don't some ipv6 addresses make use of eui /64 modifer format or don't contain FF FE ?

example:

2001:0db8:3c4d:0015:0000:0000:abcd:ef12

the anwser is prob real simple but i just can't seem to get it any help would be appreciated thanks

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Comments

vinbuck

The answer is...it's up to you. When you configure the equipment, you can choose to fill in the 64-bit host portion of the address dynamically using EUI-64, or you can statically define the last 64 bits of the address. Alternatively, you can also use DHCPv6 to assign host addresses. FFFE in the middle of the last 64 bits is a surefire giveaway that EUI-64 is being used.

SubnetZero

Hello!

The network ID is administratively assigned, and the host ID can be configured manually or auto-configured by any of the following methods:

1) Using a randomly generated number
2) Using DHCPV6
3) Using the Extended Unique Identifier (EUI-64) format.

Everyone does things differently but for hosts I recommend DHCPV6 over the other two methods.

For network gear I have mixed feelings on using statically assigned and the modified eui-64.

For example let's say I configure the following IPv6 address on my router using EUI-64

First let's check the MAC address

R1(config)#do sh int f0/0 | i bia
Hardware is Gt96k FE, address is 0014.1c2b.4550 (bia 0014.1c2b.4550)

Now let's configure the interface

R1(config)#ipv6 unicast-routing
R1(config)#int f0/0
R1(config-if)#ipv6 address 2001:192:10:1::/64 eui-64

Now we should see the that both addresses had the host portion generated using the eui-64 format (FF:FE)

R1(config)#do sh ipv6 int br | ex un
FastEthernet0/0 [up/up]
FE80::214:1CFF:FE2B:4550
2001:192:10:1:214:1CFF:FE2B:4550

While this is definitely cool but it's kind of long and if you were troubleshooting/debugging on another router how would you know which router this was?

*Sep 26 19:56:59.389: IPv6: SAS picked source 2001:192:10:1:214:1CFF:FE2B:4550 for 2001:192:10:1:214:1CFF:FE2B:4550 (FastEthernet0/0)
*Sep 26 19:56:59.389: IPV6: source 2001:192:10:1:214:1CFF:FE2B:4550 (local)
*Sep 26 19:56:59.389: dest 2001:192:10:1:214:1CFF:FE2B:4550 (FastEthernet0/0)
*Sep 26 19:56:59.389: traffic class 0, flow 0x0, len 100+0, prot 58, hops 64, originating
*Sep 26 19:56:59.389: IPv6: Sending via loopback
*Sep 26 19:56:59.389: IPV6: source 2001:192:10:1:214:1CFF:FE2B:4550 (FastEthernet0/0)
*Sep 26 19:56:59.389: dest 2001:192:10:1:214:1CFF:FE2B:4550
*Sep 26 19:56:59.393: traffic class 0, flow 0x0, len 100+0, prot 58, hops 64, forward to ulp
*Sep 26 19:56:59.393: IPV6: source 2001:192:10:1:214:1CFF:FE2B:4550 (local)
*Sep 26 19:56:59.393: dest 2001:192:10:1:214:1CFF:FE2B:4550 (FastEthernet0/0)
*Sep 26 19:56:59.393: traffic class 0, flow 0x0, len 100+0, prot 58, hops 64, originating
*Sep 26 19:56:59.393: IPv6: Sending via loopback
*Sep 26 19:56:59.393: IPV6: source 2001:192:10:1:214:1CFF:FE2B:4550 (FastEthernet0/0)
*Sep 26 19:56:59.393: dest 2001:192:10:1:214:1CFF:FE2B:4550
*Sep 26 19:56:59.393: traffic class 0, flow 0x0, len 100+0, prot 58, hops 64, forward to ulp
*Sep 26 19:56:59.393: IPv6: SAS picked source 2001:192:10:1:214:1CFF:FE2B:4550 for 2001:192:10:1:214:1CFF:FE2B:4550 (FastEthernet0/0)
*Sep 26 19:56:59.393: IPV6: source 2001:192:10:1:214:1CFF:FE2B:4550 (local)
*Sep 26 19:56:59.393: dest 2001:192:10:1:214:1CFF:FE2B:4550 (FastEthernet0/0)
*Sep 26 19:56:59.393: traffic class 0, flow 0x0, len 100+0, prot 58, hops 64, originating

So this is where I start thinking that manipulating this makes better sense. For example we could do the following:

R1(config)#int fa0/0
R1(config-if)# ipv6 address 2001:192:10:1::1/64

So now we've assigned the host portion ourselves [:1] which signifies Router 1

R1(config-if)#do sh ipv6 inter br
FastEthernet0/0 [up/up]
FE80::214:1CFF:FE2B:4550
2001:192:10:1::1

Notice that the link-local still using the eui-64 to generate it's own address. We can manipulate this with similar results as well:

R1(config)#int fa0/0
R1(config-if)# ipv6 address fe80::1 link-local
R1(config-if)# ipv6 address 2001:192:10:1::/64 eui-64

So even though we are using the modified eui-64 we set our link-local address manually which now supplies the 64 bits to identify the host portion of the address

R1(config)#do sh ipv6 inter br
FastEthernet0/0 [up/up]
FE80::1
2001:192:10:1::1

Anyway I'm rambling on now...

Cheers!

drumrolfe

^This guy.....
BTW are you the subnet zero who put up his study guide on Cisco's Learning network?

SubnetZero

drumrolfe wrote: »

^This guy.....
BTW are you the subnet zero who put up his study guide on Cisco's Learning network?

No I use my real name on those forums...

orange_badger

wow great response thanks very much for everyone’s expertise u guys have cleared up this query for me