IPv6 Statefull configuration

Posted on 2014-12-04
Medium Priority
Last Modified: 2014-12-08
I have a DHCPv6 on my network IPv6 clients get IPv6 address but no default gateway.
My gateway is a SVI on a nexus switch. What must I configure on the nexus so my clients can get default gateway via RA.
Question by:ciscosupp
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LVL 32

Expert Comment

ID: 40482753
Correct, if the Nexus is the GW then it will send out the RAs once configured. You may wish to send additional information to the clients via setting the O and M bits.

 The traditional sequence of events is:
A router attached to a network will announce it as a router that is sending periodic RA's (Router Advertisements). If the router wishes the attached clients to use DHCPv6 for acquiring an IPv6 address, it can signal that with setting the `O' and `M' bits in the Router Advertisement (RA). The two bits of importance within a Router Advertisement (RA) are:

a. M-bit: 1-bit "Managed address configuration" flag. When set, clients use DHCPv6 protocol for address configuration.

b. O-bit: 1-bit "Other stateful configuration" flag. When set, hosts use DHCPv6 to obtain `other' (non-address) information.


harbor235 ;}

Author Comment

ID: 40483167
Thanks for info
I have set the M-bit and O-bit but what setting must I add so that the client gets a GW.
All clients get ipv6 and DNS setting from DHCPv6 except for the GW.
Please advice
LVL 32

Expert Comment

ID: 40483505
There are several ways to receive GW info, you can assign the GW manually, you can receive it via a RA or a RS, or you can receive it via the DHCPV6 server. So, if your DHCPV6 server is only configured to send an IP address and/or DNS resolver information then it would receive the GW info from the RA or RS. If your DHCPV6 server is setup to send all the information then that's how the client will receive the GW info.

If you have your DHCPV6 server sending an ip address and DNS resolver info only, and you are not receiving the GW info,
then how is the GW routed interface configured? Are you filtering RAs?

Please provide information on you or configuration and what device provides which services?

Iassume that all devices have IPV6 properly configured? OS types?

harbor235 ;}

Author Comment

ID: 40483672
Remember DHCPv6 does not support a filed for DW otherwise I would configure it.
I don’t filter RAs
See attached config of my SVI.
Clients are windows 7 machines.
LVL 32

Accepted Solution

harbor235 earned 2000 total points
ID: 40484071
Yo are right, I was mixing up v4 and v6 regarding the dhcp service. What OS is the client?

What happens when you run wireshark, you can see the RA advertised with L flag? L means the router is announcing itself as the GW

Linux: ip -6 neigh show
Windows: from cmd window
                         netsh> interface ipv6
                         netsh> show route         - dispaly v6 routing table look for ::/0

OSs vary on how GW can be configured, it would help to know what you have and which dhcpv6 server you are using.

harbor235 ;}

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