Configuring DHCPv6 in 3560

[Jermy Franklin]

Hi,

I am trying to configure DHCPv6 pool in my cisco 3560 switch but failed.

Can somebody please help me in configuring it with some example.

Thanks,

Jermy

[Julio Carvajal]

Hello Jermy,

What do you mean by failed?

What commands have you set?

[Jermy Franklin]

Hi,

I've enabled IPv6 like

sdm prefer dual-ipv4-and-ipv6 default

ipv6 unicast-routing

This is my DHCP configuration on my 3560 switch.

ipv6 dhcp pool testipv6

address prefix 2002::/124 lifetime infinite infinite

And this is my vlan configuration

interface Vlan6
no ip address
ipv6 address 2002::1/124
ipv6 enable
ipv6 dhcp server testipv6 rapid-commit

After this when I configured a interface under this vlan 6 my laptop which is hving windows 7 is not getting a ipv6 address of that dhcp pool.

Even I tried by assigning a static ipv6 address to my laptop it is not pinging to gateway.

Kindly advice.

Thanks

[James Leinweber · Accepted solution]

Note that 2002::/16 is the IANA 6to4 prefix (rfc3056), and clients will expect to allocate their own /48 prefix under it using their IPv4 address as a suffix.   I have no idea how that will interact with DHCPv6 on either the switch or the client, but I suspect very badly.   Try a different prefix.  If you want something which is not globally routable, maybe use either the example prefix 2001:db8::/32 or a Unique Local Address prefix fd00::/7 with a pseudo-random 40 bit suffix to make a /48 (rfc 4193).

-- Jim Leinweber, WI State Lab of Hygiene

[Jermy Franklin]

Thanks  Buddy.. It is working as static but need to check with DHCPv6.

[Jermy Franklin]

Hi,

I've changed the configuration but still my client pc is not getting ipv6 from my defined DHCP pool.

Configuartion as follows:

DHCP config:

ipv6 dhcp pool dhcpv6

prefix-delegation pool mypool

Vlan config:

int vl 1

ipv6 address 2001:db8::1/64

ipv6 dhcp server dhcpv6

no sh

local pool:

ipv6 local pool mypool 2001:db8::/56 64

Then kept my client laptop in interface 1 which is configured under vlan 1.

But result ends as failed by not getting ipv6 address from my preferred dhcp pool and interesting thing is my laptop getting link local ipv6 address and gateway as my switch vlan interface link-local ip.

So can anybody help me on this to resolve..

Thanks

Jermy

[James Leinweber]

Dunno about failure to assign global addresses from your DHCPv6 pool, sorry.

However, in IPv6 the laptop will always have and always use an fe80::/64 link-local address in addition to any global address.  Unlike in IPv4 zeroconf (169.254.0.0/16) in IPv6 the clients continue to use link-local addresses even after completing DHCP or SLAAC or static configuration of larger-scope addresses.

Similarly, in IPv6 the only source of the gateway address is the link-local address of the sending router in the router advertisement.  IPv6 gateways are not a payload option in either RA's nor in DHCPv6.  So seeing your upstream gateway be fe80::SOMETHING is also normal; after all, the gateway has to be on-link with you.   If the gateway happens to have a static global address in addition to its link-local address a staticly configured route is at liberty to point at that instead, but all dynamic clients will always use the link-local address from the RA.

Replacing ARP with ICMPv6 multicast neighbor discovery,  the role of RA flags in controlling DHCP,  and the role of RA's in inferring gateways, are the 3 biggest on-link differences between operating IPv4 and IPv6.

-- Jim Leinweber

[cadet alain]

Hi,

redo the config you had before( but without rapid-commit) but just change the prefix and sniff your NIC then send the capture file here.

Regards

Alain

Don't forget to rate helpful posts.

[Julio Carvajal]

Hello,

I totally agree with James, this just does not look right.

Try to use a different prefix and let us know how it goes,

[mhnedirli]

can you post your config


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