Connecting the world…

XS4ALL, Cisco 877 and IPv6

A while ago my ISP XS4ALL started with the distribution of IPv6 prefixes to their customers. So as a network engineer I wanted to have my own /48 prefix. Sadly I didn’t had time to start testing at the beginning of the IPv6 “launch”.

Last week I found some time to start my testing. I started by configuring my external DSL interface to run in dual-stack mode. The IPv4 configuration is straightforward and isn’t part of this article.

Below you see the basic configuration of the Dialer interface to enable IPv6. The commands configure the Dialer interface as DHCP client (autoconfiguration on the interface) and the prefix delegation name is “my_prefix”.

interface Dialer1
ipv6 address autoconfig
ipv6 enable
ipv6 dhcp client pd my_prefix rapid-commit

You can check the allocation of the IPv6 address prefix with the following command:

C877W#show ipv6 general-prefix
IPv6 Prefix prefix_ipv6, acquired via DHCP PD
2001:980:3441::/48 Valid lifetime , preferred lifetime
BVI1 (Address command)

More information about the allocation can also be obtained with the following command:

C877W#show ipv6 dhcp interface
Dialer1 is in client mode
State is OPEN
Renew will be sent in 00:11:48
List of known servers:
Reachable via address: FE80::90:1A00:1A1:88E6
DUID: 000200000A4C453332302F373435414333334558322F01
Preference: 0
Configuration parameters:
IA PD: IA ID 0x00100001, T1 3600, T2 5760
Prefix: 2001:980:3441::/48
preferred lifetime 7200, valid lifetime 7200
expires at Jan 31 2011 12:24 PM (4310 seconds)
DNS server: 2001:888:0:6::66
DNS server: 2001:888:0:9::99
Information refresh time: 0
Prefix name: my_prefix
Rapid-Commit: enabled

Now you need to configure IPv6 routing, especially the default route and enabling unicast-routing, with the following commands:

ipv6 unicast-routing
ipv6 route ::/0 Dialer1

The next step involves the configuration of the LAN interface to support IPv6. RFC 3177 recommends the delegation of /48 prefixes to home network subscribers, small and large organizations. It looks like my ISP follows that recommendation. The same RFC states that a /64 prefix should be assigned to different host subnets. So I can configure 2^16 host subnets and each subnet can contain 2^64 IPv6 addresses. Seems enough for my home environment.

The inside interface (a Bridged Virtual Interface in my scenario) is configured with the following /64 prefix.

ipv6 address my_prefix 0:0:0:1::/64 eui-64

You can use the following command to look at the IPv6 configuration of the different interfaces.

C877W#show ipv6 interface brief
BVI1                       [up/up]
Dialer1                    [up/up]

The basic IPv6 configuration is done. The next step is testing IPv6 connectivity via an IPv6 ping to

C877W#ping ipv6 2a00:1450:8005::68 source bvi1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2A00:1450:8005::68, timeout is 2 seconds:
Packet sent with a source address of 2001:980:3441:1::FFFF
Success rate is 100 percent (5/5), round-trip min/avg/max = 24/25/28 ms

Ping can reply with different characters. The characters are listed below.

! Each exclamation point indicates receipt of a reply
. Each period indicates that the network server timed out while waiting for a reply
? Unknown error
@ Unreachable for unknown reason
A Administratively unreachable. Usually, this output indicates that an access list is blocking traffic
B Packet too big
H Host unreachable
N Network unreachable (beyond scope)
P Port unreachable
R Parameter problem
T Time exceeded
U No route to host

Prefix Delegation (PD) in IPv6 is very useful when deploying IPv6 in the network. The deployment of IPv6 to hosts also involves the distribution of additional parameters, like IPv6 DNS servers. The next step involves the configuration of Router Advertisement (RA) messages on the Bridged Virtual Interface.

I configured an DHCPv6 pool and configured the BVI interface as DHCP server interface with the following commands:

ipv6 dhcp pool ipv6_inside
dns-server 2001:888:0:6::66
interface BVI1
ipv6 address my_prefix 0:0:0:1::/64 eui-64
ipv6 nd other-config-flag
ipv6 dhcp server ipv6_inside rapid-commit

The other-config-flag sets the O-bit in IPv6 RA messages to inform hosts that they can use autoconfiguration for their IPv6 configuration. This results in DHCPv6 INFORMATION-REQUEST messages from the hosts to the DHCPv6 server. The router will reply to these message, because it is configured as DHCP server for the prefix.

I started testing, but my hosts didn’t receive any IPv6 address and debugging IPv6 on the router didn’t output any useful information. Of course the hosts couldn’t receive any IPv6 address, because of the well-known bug CSCej50923 (CCO ID required) on BVI interface routing, which does not work for IPv6 addressing. I didn’t want to upgrade my router directly, so I created another VLAN with the appropriate Switched Virtual Interface. I configured the same commands as under the BVI interface, but this time with prefix 0:0:0:2::/64. Now I have 3 interfaces enabled for IPv6 addressing, like shown below:

C877W#show ipv6 interface brief
BVI1                       [up/up]
Dialer1                    [up/up]
Vlan2                      [up/up]

You can see the difference in the prefix between BVI1 and Vlan2. I issued a ipconfig /release6 and ipconfig /renew6 on the hosts and IPv6 is working like a perfectly.

The complete output of the ipconfig /all and a ping to can be found below.

Ethernet adapter Local Area Connection:

Connection-specific DNS Suffix  . :
Description . . . . . . . . . . . : Broadcom NetLink (TM) Gigabit Ethernet
Physical Address. . . . . . . . . : 00-25-64-F6-1C-D7
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
IPv6 Address. . . . . . . . . . . : 2001:980:3441:2:c527:8966:a47f:55d2(Preferred)
Temporary IPv6 Address. . . . . . : 2001:980:3441:2:cd4d:b38b:e861:f43(Preferred)
Link-local IPv6 Address . . . . . : fe80::c527:8966:a47f:55d2%11(Preferred)
IPv4 Address. . . . . . . . . . . :
Subnet Mask . . . . . . . . . . . :
Lease Obtained. . . . . . . . . . : Monday, January 31, 2011 4:02:01 PM
Lease Expires . . . . . . . . . . : Thursday, February 03, 2011 4:02:00 PM
Default Gateway . . . . . . . . . : fe80::21a:6dff:fe7d:b684%11
DHCP Server . . . . . . . . . . . :
DHCPv6 IAID . . . . . . . . . . . : 234890596
DHCPv6 Client DUID. . . . . . . . : 00-01-00-01-13-65-AE-74-00-25-64-F6-1C-D7

DNS Servers . . . . . . . . . . . : 2001:888:0:6::66
NetBIOS over Tcpip. . . . . . . . : Enabled
Connection-specific DNS Suffix Search List :


Pinging [2a00:1450:8005::68] with 32 bytes of data:
Reply from 2a00:1450:8005::68: time=29ms
Reply from 2a00:1450:8005::68: time=25ms
Reply from 2a00:1450:8005::68: time=25ms
Reply from 2a00:1450:8005::68: time=26ms

Ping statistics for 2a00:1450:8005::68:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 25ms, Maximum = 28ms, Average = 26ms

The following two tabs change content below.

René Jorissen

Co-owner and Solution Specialist at 4IP Solutions
René Jorissen works as Solution Specialist for 4IP in the Netherlands. Network Infrastructures are the primary focus. René works with equipment of multiple vendors, like Cisco, Aruba Networks, FortiNet, HP Networking, Juniper Networks, RSA SecurID, AeroHive, Microsoft and many more. René is Aruba Certified Edge Expert (ACEX #26), Aruba Certified Mobility Expert (ACMX #438), Aruba Certified ClearPass Expert (ACCX #725), Aruba Certified Design Expert (ACDX #760), CCNP R&S, FCNSP and Certified Ethical Hacker (CEF) certified. You can follow René on Twitter and LinkedIn.

Latest posts by René Jorissen (see all)

One Response to XS4ALL, Cisco 877 and IPv6

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.