Comcast prefix-delegation - LAN interfaces do not participate in RA

Mattias Lindgren · ‎09-06-2015

I am running a Cisco 3845 at home with IOS 151-4.M10. I get my IPv6 address space from Comcast via:

interface GigabitEthernet0/0

description Comcast Public

ipv6 address dhcp

ipv6 enable

ipv6 dhcp client pd hint ::/60

ipv6 dhcp client pd prefix-from-Comcast

ipv6 inspect v6FWOUT out

ipv6 traffic-filter v6_Access_In in

end

The LAN interfaces are able to get addresses via prefix-delegation, however I can't seem to make SLAAC work for clients attached to those interfaces.

interface GigabitEthernet0/1.1010

encapsulation dot1Q 1010

ipv6 address FE80::AAA link-local

ipv6 address prefix-from-Comcast ::A:0:0:0:1/64

ipv6 enable

ipv6 nd autoconfig prefix

ipv6 nd autoconfig default-route

end

Is there anything I'm missing? I can ping via link-local addresses, so there is no physical connectivity problems.

Seb Rupik · ‎09-07-2015

Hi there,

Looks like you have configured Gi0/1.1010 to send out RS packets to receive RAs from other routers on the link. Instead, try the following:

!

int gi0/1.1010

  no ipv6 nd autoconfig prefix

  no ipv6 nd autoconofig default-route

  ipv6 nd prefix default

!

That should ensure your switch is the one sending out RA packets with default settings.

cheers,

Seb.

Mattias Lindgren · ‎09-08-2015

Hi Seb,

Thanks for your reply. However this does not appear to resolve the issue. I have essentially reverted back to defaults:

interface GigabitEthernet0/1.1010

encapsulation dot1Q 1010

ip address 10.50.100.1 255.255.255.0

ip nat inside

ip virtual-reassembly in

ipv6 address prefix-from-Comcast ::A:0:0:0:1/64

ipv6 enable

end

The odd thing is that if I assign an address manually rather than through prefix-delegation, it still does not assign addresses, so it feels like it is more having to do with it being a sub-interface rather than it using prefix delegation. I'm wondering if it is an IOS bug at this point. Very strange! I'll keep hammering away at it.

Seb Rupik · ‎09-08-2015

Hi Mattias,

What output do you get for:

sh ipv6 int gi0/1.1010

cheers,

Seb.

Mattias Lindgren · ‎09-08-2015

I get: (edited for privacy)

#show ipv6 interface gi0/1.1010

GigabitEthernet0/1.1010 is up, line protocol is up

IPv6 is enabled, link-local address is FE80::226:CBFF:FEE9:BB31

No Virtual link-local address(es):

General-prefix in use for addressing

Global unicast address(es):

2601:xxxx:300:AAA::1, subnet is 2601:xxxx:300:AAA::/64 [CAL/PRE]

valid lifetime 207758 preferred lifetime 207758

Joined group address(es):

FF02::1

FF02::2

FF02::1:FF00:1

FF02::1:FFE9:BB31

MTU is 1500 bytes

ICMP error messages limited to one every 100 milliseconds

ICMP redirects are enabled

ICMP unreachables are sent

Input features: Common pak subblock

Output features: Firewall Inspection

ND DAD is enabled, number of DAD attempts: 1

ND reachable time is 30000 milliseconds (using 30000)

ND advertised reachable time is 0 (unspecified)

ND advertised retransmit interval is 0 (unspecified)

ND router advertisements are sent every 200 seconds

ND router advertisements live for 1800 seconds

ND advertised default router preference is Medium

Hosts use stateless autoconfig for addresses.

Seb Rupik · ‎09-08-2015

That output looks good.

If you run 'debug ipv6 nd' whilst a device is connected to the LAN, do you see any ICMPv6-ND messages relating to receiving RS packets?

Likewise if you run tcpdump/ wireshark on a connecting device, do you see Router Solicitations being sent? What about the periodic Router Advertisments packets every 200 seconds?

cheers,

Seb.