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I understand that stateful DHCPv6 cannot provide hosts with a default router, as DHCPv4 could. Hosts would need to determine the default router based off of the information in RA packets.

In my lab, I have a Cisco 7200 router (R1) set up as a DHCPv6 server. I can provide another Cisco router (R2) with an IPv6 address. But R2 does not install a IPv6 route to R1. I can ping R1's link-local address, but not its global unicast address (I receive a "No valid route for destination" error). In R2's IPv6 routing table, there is only an LC route.

I set up an additional router, R3, connected to R1. However, R3 is set up for SLAAC. Given that it's autoconfig, an NDp route is installed in the routing table and I can ping the global address just fine.

My question is, how can I configure a Cisco router to both serve as a DHCPv6 client and also generate a route based off of RA packets?

My R1 configuration:

ipv6 dhcp pool aPOOL
   address prefix 2001:DB8:ACAD::/64 lifetime infinite infinite

interface GigabitEthernet0/0
   no ip address
   duplex full
   speed 1000
   media-type gbic
   negotiation auto
   ipv6 address FE80::1 link-local
   ipv6 address 2001:DB8:ACAD::1/64
   ipv6 nd managed-config-flag
   ipv6 dhcp server DHCPv6_POOL

My R2 configuration:

interface GigabitEthernet0/0
   no ip address
   duplex full
   speed 1000
   media-type gbic
   negotiation auto
   ipv6 address dhcp
   ipv6 address FE80::1:1 link-local
   ipv6 enable

Thank you!

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    Apr 1, 2018 at 20:30

2 Answers 2

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If you take a look at RFC4862 (IPv6 Stateless Address Autoconfiguration) this behavior might become a little clearer:

The autoconfiguration process specified in this document applies only
to hosts and not routers.  Since host autoconfiguration uses
information advertised by routers, routers will need to be configured
by some other means.

So in other words: The router behaves as expected.

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My instructor answered my question. Cisco routers will not insert an IPv6 default route into their routing table unless you do a "no ipv6 unicast-routing" command. I tested this in GNS3 and I can now ping R1's global address from R2.

This is apparently the same situation with IPv4, but I haven't tested it yet.

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