Tag Archives: slaac

IPv6 and Junos – Stateful Auto-configuration with DHCPv6

Reading Time: 4 minutes

As part of my on-going IPv6 testing, I was asked to look into stateful auto-configuration for devices and host using DHCPv6. I had already looked into Stateless Address Auto configuration and looked into another method of providing stateful auto-configuration using a Dual Stacked DHCP server. This time I’ll be looking into how this could be done using Juniper hardware, to be specific Juniper SRX series routers. If you haven’t used DHCP before my other DHCP related post gave an explanation on what DHCP is and how DHCPv6 communications work slightly different to DHCPv4. With that in mind, I won’t be going over what DHCP is again, but instead I’ll be going straight into the good stuff!

Lets get cracking 😀

For this test I had simple topology; I used a Juniper SRX220 as the DHCP server and a single ESXi Ubuntu 14.04LTS hosts connected on port ge-0/0/0 as the client.

Firstly, with the SRX, I had to enabled IPv6 flow mode. By default, IPv6 IS NOT enabled. You enable IPv6 flow mode by running the command set security forwarding-options family inet6 mode flow-based, once committed you’ll need to reboot the device for the change to take effect. When the SRX is finished booting you can confirm IPv6 flows will be able to be permitted by using show security flow status:

[email protected]> show security flow status 
  Flow forwarding mode:
    Inet forwarding mode: flow based
    Inet6 forwarding mode: flow based
    MPLS forwarding mode: drop
    ISO forwarding mode: drop
  Flow trace status
    Flow tracing status: off
  Flow session distribution
    Distribution mode: RR-based
  Flow ipsec performance acceleration: off
  Flow packet ordering
    Ordering mode: Hardware

Now that we know we can actually get stateful IPv6 flows traversing the SRX, we can start with enabling the SRX as a DHCPv6 server.

Under the system services dhcp-local-server stanza, we will need to confirm that we’ll be using DHCPv6 and set the interface(s) that will be requesting addresses. Additionally there are a few optional commands. For my example I’ve set the max limit of DHCP clients to 100 by using the interface-client-limit statement, and by default there are no limits on amount of clients that can request an address.

[email protected]# show system services 
dhcp-local-server {
    dhcpv6 {
        overrides {
            interface-client-limit 100;
        }
        group v6 {
            interface vlan.100;
        }
    }
}

Next, under the access address-assignment stanza is where we’ll set the prefix pool that will be advertised to host, and your IP range. In addition, within this stanza you’re able to set other DHCP details such as lease time, grace period and dns-server under dhcp-attributes. The attributes are optional however they should be looked into and configured according to your own requirements.

[email protected]# show access   
address-assignment {
    pool v6 {
        family inet6 {
            prefix 2001:192:168:1::/64;
            range dhcpv6-range {
                low 2001:192:168:1::200/128;
                high 2001:192:168:1::299/128;
            }
            dhcp-attributes {
                maximum-lease-time 120;
                grace-period 3600;
            }
        }
    }
}

We need to set the SRX so that the router advertises our IPv6 prefix on the correct interface, and in addition, by adding the statement managed-configuration, the router will be both stateful (DHCP) and stateless (SLAAC) address assignments. Finally, in order for the DHCPv6 server to allow DHCPv6 requests, a security policy is needed to enable DHCPv6 traffic.

ProtocolsSecurity Zone
[email protected]# show protocols 
router-advertisement {
    interface vlan.100 {
        managed-configuration;
        prefix 2001:192:168:1::/64;
    }
}
[email protected]# show security zone security-zone internal {
    tcp-rst;
    interfaces {
        vlan.100 {
            host-inbound-traffic {
                system-services {
                    dhcpv6;
                }
            }
        }
    }
}

With SRX configured, we can now check the client side to make sure it’s enabled for DHCP. On the client, we have to set its interface to listening for DHCP packets. For IPv6 we’ll need to set the interface to DHCP under /etc/network/interfaces.

[email protected]:~$ cat /etc/network/interfaces
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).
{...}
auto eth1
iface eth1 inet dhcp

# This is an autoconfigured IPv6 interface
iface eth0 inet6 auto

auto eth1
iface eth1 inet6 dhcp

Now that we have both the SRX and the client configured, we can bring it all together and run some tests!

Verification Testing

On the client, we’ll request an IP address from the SRX by running dhclient eth1 -6 -v and can confirm that an address has been successful assigned by doing an ifconfig

Requesting an addressifconfig eth1
[email protected]:~$ sudo dhclient eth1 -6 -v 
Internet Systems Consortium DHCP Client 4.2.4
Copyright 2004-2012 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Bound to *:546
Listening on Socket/eth1
Sending on   Socket/eth1
PRC: Soliciting for leases (INIT).
XMT: Forming Solicit, 0 ms elapsed.
XMT:  X-- IA_NA 29:4f:26:c5
XMT:  | X-- Request renew in  +3600
XMT:  | X-- Request rebind in +5400
XMT:  | X-- Request address 2001:192:168:1::111.
XMT:  | | X-- Request preferred in +7200
XMT:  | | X-- Request valid in     +10800
XMT:  | X-- Request address 2001:192:168:1::200.
XMT:  | | X-- Request preferred in +7200
XMT:  | | X-- Request valid in     +10800
XMT: Solicit on eth1, interval 1060ms.
RCV: Advertise message on eth1 from fe80::120e:7eff:fe4e:2e88.
RCV:  X-- IA_NA 29:4f:26:c5
RCV:  | X-- starts 1452250973
RCV:  | X-- t1 - renew  +60
RCV:  | X-- t2 - rebind +96
RCV:  | X-- [Options]
RCV:  | | X-- IAADDR 2001:192:168:1::200
RCV:  | | | X-- Preferred lifetime 120.
RCV:  | | | X-- Max lifetime 120.
RCV:  X-- Server ID: 00:02:00:00:05:83:43:46:34:37:31:33:41:4b:30:32:38
RCV:  Advertisement recorded.
PRC: Selecting best advertised lease.
PRC: Considering best lease.
PRC:  X-- Initial candidate 00:02:00:00:05:83:43:46:34:37:31:33:41:4b:30:32 (s: 153, p: 0).
XMT: Forming Request, 0 ms elapsed.
XMT:  X-- IA_NA 29:4f:26:c5
XMT:  | X-- Requested renew  +3600
XMT:  | X-- Requested rebind +5400
XMT:  | | X-- IAADDR 2001:192:168:1::200
XMT:  | | | X-- Preferred lifetime +7200
XMT:  | | | X-- Max lifetime +7500
XMT:  V IA_NA appended.
XMT: Request on eth1, interval 930ms.
RCV: Reply message on eth1 from fe80::120e:7eff:fe4e:2e88.
RCV:  X-- IA_NA 29:4f:26:c5
RCV:  | X-- starts 1452250974
RCV:  | X-- t1 - renew  +60
RCV:  | X-- t2 - rebind +96
RCV:  | X-- [Options]
RCV:  | | X-- IAADDR 2001:192:168:1::200
RCV:  | | | X-- Preferred lifetime 120.
RCV:  | | | X-- Max lifetime 120.
RCV:  X-- Server ID: 00:02:00:00:05:83:43:46:34:37:31:33:41:4b:30:32:38
PRC: Bound to lease 00:02:00:00:05:83:43:46:34:37:31:33:41:4b:30:32:38:31.
[email protected]:~$ ifconfig eth1
eth1      Link encap:Ethernet  HWaddr 00:0c:29:4f:26:c5  
          inet6 addr: fe80::20c:29ff:fe4f:26c5/64 Scope:Link
          inet6 addr: 2001:192:168:1::200/64 Scope:Global
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:12342 errors:0 dropped:0 overruns:0 frame:0
          TX packets:11980 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:4052626 (4.0 MB)  TX bytes:3303461 (3.3 MB)

Having confirmed that an IP address from DHCP pool has been assigned on the client, we can now look on SRX to see what has happened there!

Firstly, I checked to see if I could see the session flow from the client to SRX by running show security flow session. As the output below shows, as per RFC3315, DHCPv6 communications are done on UDP ports 546 (clients) and 547 (server/relay) and via link-local addresses.

[email protected]> show security flow session       
Session ID: 1, Policy name: self-traffic-policy/1, Timeout: 1800, Valid
  In: 10.1.0.17/46789 --> 10.1.0.158/22;tcp, If: ge-0/0/7.0, Pkts: 5631, Bytes: 416401
  Out: 10.1.0.158/22 --> 10.1.0.17/46789;tcp, If: .local..0, Pkts: 3109, Bytes: 389005

Session ID: 9, Policy name: self-traffic-policy/1, Timeout: 54, Valid
  In: fe80::120e:7eff:fe4e:2e88/547 --> fe80::20c:29ff:fe4f:26c5/546;udp, If: .local..0, Pkts: 2, Bytes: 288
  Out: fe80::20c:29ff:fe4f:26c5/546 --> fe80::120e:7eff:fe4e:2e88/547;udp, If: vlan.100, Pkts: 0, Bytes: 0
Total sessions: 2

We only get two show commands with a DHCP server, whether it’s v4 or v6, show dhcpv6 server binding and show dhcpv6 server statistics.

  • show dhcpv6 server binding provides details on the address that has been assigned to a client, which including; MAC address, Prefix, Lease time, current state and interface.
  • show dhcpv6 server statistics, as the name suggests, provides figures on sent and receive messages between the server and clients.
DHCPv6 BindingsDHCPv6 Statistics
[email protected]> show dhcpv6 server binding        
Prefix                  Session Id  Expires  State    Interface    Client DUID
2001:192:168:1::200/128 2           74       BOUND    vlan.100     LL_TIME0x1-0x1ddd0462-00:0c:29:4f:26:c5
[email protected]> show dhcpv6 server statistics 
Dhcpv6 Packets dropped:
    Total               0

Messages received:
    DHCPV6_DECLINE             0
    DHCPV6_SOLICIT             1
    DHCPV6_INFORMATION_REQUEST 0
    DHCPV6_RELEASE             0
    DHCPV6_REQUEST             1
    DHCPV6_CONFIRM             0
    DHCPV6_RENEW               0
    DHCPV6_REBIND              0
    DHCPV6_RELAY_FORW          0
    DHCPV6_RELAY_REPL          0

Messages sent:
    DHCPV6_ADVERTISE           1
    DHCPV6_REPLY               1
    DHCPV6_RECONFIGURE         0
    DHCPV6_RELAY_REPL          0

For completeness, I had the client release the assigned address to check the statistics, just to make sure I did see an increment change.

Releasing Assigned AddressDHCPv6 Statistics
[email protected]:~$ sudo dhclient -6 -v -r eth1
Internet Systems Consortium DHCP Client 4.2.4
Copyright 2004-2012 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Bound to *:546
Listening on Socket/eth1
Sending on   Socket/eth1
XMT: Forming Release, 0 ms elapsed.
XMT:  X-- IA_NA 29:4f:26:c5
XMT:  | X-- Release Address 2001:192:168:1::200
XMT:  V IA_NA appended.
XMT: Release on eth1, interval 1070ms.
RCV: Reply message on eth1 from fe80::120e:7eff:fe4e:2e88.
RCV:  X-- Server ID: 00:02:00:00:05:83:43:46:34:37:31:33:41:4b:30:32:38
[email protected]> show dhcpv6 server statistics    
Dhcpv6 Packets dropped:
    Total               0

Messages received:
    DHCPV6_DECLINE             0
    DHCPV6_SOLICIT             1
    DHCPV6_INFORMATION_REQUEST 0
    DHCPV6_RELEASE             1
    DHCPV6_REQUEST             1
    DHCPV6_CONFIRM             0
    DHCPV6_RENEW               1
    DHCPV6_REBIND              0
    DHCPV6_RELAY_FORW          0
    DHCPV6_RELAY_REPL          0

Messages sent:
    DHCPV6_ADVERTISE           1
    DHCPV6_REPLY               3
    DHCPV6_RECONFIGURE         0
    DHCPV6_RELAY_REPL          0

And with that a DHCPv6 Server has been configured using a Juniper SRX series router!

I’ve included a useful show command and the set commands that I used in my example below 🙂

Operational CommandsSet Commands
show security flow session
show dhcpv6 server binding
show dhcpv6 server statistics
clear dhcpv6 server binding
clear dhcpv6 server statistics
set security forwarding-options family inet6 mode flow-based

set system services dhcp-local-server dhcpv6 overrides interface-client-limit 200
set system services dhcp-local-server dhcpv6 group v6 interface vlan.100

set protocols router-advertisement interface vlan.100 prefix 2001:192:168:1::/64

set access address-assignment pool v6 family inet6 prefix 2001:192:168:1::/64
set access address-assignment pool v6 family inet6 range dhcpv6-range low 2001:192:168:1::200/128
set access address-assignment pool v6 family inet6 range dhcpv6-range high 2001:192:168:1::299/128
set access address-assignment pool v6 family inet6 dhcp-attributes maximum-lease-time 120
set access address-assignment pool v6 family inet6 dhcp-attributes grace-period 3600

set security zones security-zone internal interfaces vlan.100 host-inbound-traffic system-services dhcpv6

More in-depth detailed information can be found on Juniper’s TechLibrary pages

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Configuring a Dual Stacked DHCP Server

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As part of my IPv6 Testing, I needed to test whether we would either use SLAAC or DHCPv6 in a particular situation. Having never setup a DHCP server before, of course, I had to write a post on how I did it 😀

Dynamic Host Configuration Protocol or DHCP is defined in RFC2131:

The Dynamic Host Configuration Protocol (DHCP) provides configuration parameters to Internet hosts. DHCP consists of two components: a protocol for delivering host-specific configuration parameters from a DHCP server to a host and a mechanism for allocation of network addresses to hosts.

DHCP supports three mechanisms of IP address allocation; Automatic, Dynamic and Manual allocation. RFC2131: describes how each of these mechanisms works within the DHCP process

Dynamic allocation is the only one of the three mechanisms that allows automatic reuse of an address that is no longer needed by the client to which it was assigned. Thus, dynamic allocation is particularly useful for assigning an address to a client that will be connected to the network only temporarily or for sharing a limited pool of IP addresses among a group of clients that do not need permanent IP addresses. Dynamic allocation may also be a good choice for assigning an IP address to a new client being permanently connected to a network where IP addresses are sufficiently scarce that it is important to reclaim them when old clients are retired. Manual allocation allows DHCP to be used to eliminate the error-prone process of manually configuring hosts with IP addresses in environments where (for whatever reasons) it is desirable to manage IP address assignment outside of the DHCP mechanisms.

In a nutshell:

  • Automatic allocation; the DHCP process will assign a permanent IP address to the host/device.
  • Dynamic allocation; the DHCP assigns an IP address to a client for a limited period of time or until the client release the address.
  • Manual allocation; the a client’s IP address is assigned by the network administrator, and DHCP is used simply to convey the assigned address to the client.

With DHCPv6 the communication process between server and client is a little different compared DHCPv4, as explained in RFC3315:

Clients and servers exchange DHCP messages using UDP. The client uses a link-local address or addresses determined through other mechanisms for transmitting and receiving DHCP messages. DHCP servers receive messages from clients using a reserved, link-scoped multicast address. A DHCP client transmits most messages to this reserved multicast address, so that the client need not be configured with the address or addresses of DHCP servers.

To allow a DHCP client to send a message to a DHCP server that is not attached to the same link, a DHCP relay agent on the client’s link will relay messages between the client and server. The operation of the relay agent is transparent to the client and the discussion of message exchanges in the remainder of this section will omit the description of message relaying by relay agents. Once the client has determined the address of a server, it may under some circumstances send messages directly to the server using unicast.

NOTE
For more in-depth detail about the DHCP and DHCPv6, I would suggest looking into RFC2131 and RFC3315 respectfully.

For this testing, I used a two ESXi Ubuntu 14.04LTS Hosts, one as the DHCP server and client, and the other was a Juniper EX4200 connecting them together. The switch configuration is extremely basic, both devices are in the same Vlan and the Vlan has a layer-3 interface IPv4: 192.168.1.1/24 and IPv6: 2001:192:168:1::1/64.

With all the talk out of way.. Let’s get cracking 🙂

You will need to have sudo or root privileges

Firstly, a static IPv4 and IPv6 will need to be set on the interface that will be advertising the DHCP to the LAN. For my example I’m using eth1

[email protected]:~$ ifconfig -a eth1
eth1      Link encap:Ethernet  HWaddr 00:0c:29:d3:ac:77  
          inet addr:192.168.1.2  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: fe80::20c:29ff:fed3:ac77/64 Scope:Link
          inet6 addr: 2001:192:168:1::2/64 Scope:Global
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:8 errors:0 dropped:0 overruns:0 frame:0
          TX packets:43 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:1308 (1.3 KB)  TX bytes:4204 (4.2 KB)

The DHCP package is available via the apt-get repository

sudo apt-get install isc-dhcp-server

You will need to edit /etc/default/isc-dhcp-server and set the NIC that you want to run DHCP from. In addition, you need to set options with “-6” flag to tell the package we’ll be running IPv6. For my server, I’ll be using interface “eth1”. Make you use the appropriate NIC in your configuration.

[email protected]:~$ cat /etc/default/isc-dhcp-server 
# Defaults for isc-dhcp-server initscript
# sourced by /etc/init.d/isc-dhcp-server
# installed at /etc/default/isc-dhcp-server by the maintainer scripts

#
# This is a POSIX shell fragment
#

# Path to dhcpd's config file (default: /etc/dhcp/dhcpd.conf).
#DHCPD_CONF=/etc/dhcp/dhcpd.conf

# Path to dhcpd's PID file (default: /var/run/dhcpd.pid).
#DHCPD_PID=/var/run/dhcpd.pid

# Additional options to start dhcpd with.
#    Don't use options -cf or -pf here; use DHCPD_CONF/ DHCPD_PID instead
OPTIONS="-6"

# On what interfaces should the DHCP server (dhcpd) serve DHCP requests?
#    Separate multiple interfaces with spaces, e.g. "eth0 eth1".
INTERFACES="eth1"

From doing some digging, unfortunately the original isc-dhcp-server doesn’t allow you to run IPv4 and IPv6 under the same config file. I had to create a new file and edit it to be IPv6 specific. I backed the original dhcpd.conf file and created a new dhcpd6.conf file; the two files should look similar to the below if you have a simple set up like myself.

Note
With a DHCP server you can have the server configured to set DNS, hostnames and other administrative settings. You can see examples of this if you look at the full original dhcpd.conf file. This is out of scope of what I was testing currently, but with knowing what else I’ll be testing in the future I’ll likely shown how in a future post 🙂
dhcpd6.confdhcpd.conf
[email protected]:~$ cat /etc/dhcp/dhcpd6.conf 
# The ddns-updates-style parameter controls whether or not the server will
# attempt to do a DNS update when a lease is confirmed.
ddns-update-style none;

# Option definitions common to all supported networks...
default-lease-time 600; 
max-lease-time 7200; 

# This DHCP server is the official DHCP server for the local network
authoritative;

# Use this to send dhcp log messages to a different log file (you also
# have to hack syslog.conf to complete the redirection).
log-facility local7;
 
# Subnet declaration
subnet6 2001:192:168:1::/64  {
    range6 2001:192:168:1::110 2001:192:168:1::120;
}
[email protected]:~$ cat /etc/dhcp/dhcpd.conf 
#
# Sample configuration file for ISC dhcpd for Debian
#
# Attention: If /etc/ltsp/dhcpd.conf exists, that will be used as
# configuration file instead of this file.
#
#

# The ddns-updates-style parameter controls whether or not the server will
# attempt to do a DNS update when a lease is confirmed. We default to the
# behavior of the version 2 packages ('none', since DHCP v2 didn't
# have support for DDNS.)
ddns-update-style none;

default-lease-time 600;
max-lease-time 7200;

# If this DHCP server is the official DHCP server for the local
# network, the authoritative directive should be uncommented.
authoritative;

# Use this to send dhcp log messages to a different log file (you also
# have to hack syslog.conf to complete the redirection).
log-facility local7;

# This is a very basic subnet declaration.

subnet 192.168.1.0 netmask 255.255.255.0 {
  range 192.168.1.110 192.168.1.120;
}

An DHCPv6 lease file will need to be created because, unlike IPv4, there isn’t a predefined file. In addition this file will need to have its owner changed to dhcpd daemon. This is because the daemon will need write, read and execute permissions

sudo touch /var/lib/dhcp/dhcpd6.leases
sudo chown dhcpd:dhcpd /var/lib/dhcp/dhcpd6.leases

To finish up on the server, we will need to start the DCHP processes

sudo service isc-dhcp-server start
sudo service isc-dhcp-server6 start

Once this has been done, the server is configured. Next we will hop to the other VM to see if we can get some IP addresses assigned!

Once on the client, we have to set its interface to listening for DHCP packets. Under /etc/network/interfaces both for IPv4 and IPv6 we will need to DHCP.

[email protected]:~$ cat /etc/network/interfaces
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).
{...}
auto eth1
iface eth1 inet dhcp

# This is an autoconfigured IPv6 interface
iface eth0 inet6 auto

auto eth1
iface eth1 inet6 dhcp

Once this has been set, the interface will automatically pick up an address. If you’re like me and want to see everything, you can manually release any addresses learnt by using the following commands: for IPv6 dhclient -6 -v -r eth1 and for IPv4 dhclient -v -r eth1

dhclient -v -r eth1dhclient -6 -v -r eth1
[email protected]:~$ sudo dhclient -v -r eth1
[sudo] password for marquk01: 
Internet Systems Consortium DHCP Client 4.2.4
Copyright 2004-2012 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on LPF/eth1/00:0c:29:4f:26:c5
Sending on   LPF/eth1/00:0c:29:4f:26:c5
Sending on   Socket/fallback
DHCPRELEASE on eth1 to 192.168.1.2 port 67 (xid=0x45baa909)
[email protected]:~$ sudo dhclient -6 -v -r eth1
Internet Systems Consortium DHCP Client 4.2.4
Copyright 2004-2012 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Bound to *:546
Listening on Socket/eth1
Sending on   Socket/eth1
RTNETLINK answers: Cannot assign requested address
XMT: Forming Release, 0 ms elapsed.
XMT:  X-- IA_NA 29:4f:26:c5
XMT:  | X-- Release Address 2001:192:168:1::111
XMT:  V IA_NA appended.
XMT: Release on eth1, interval 1000ms.
RCV: Reply message on eth1 from fe80::20c:29ff:fed3:ac77.
RCV:  X-- Server ID: 00:01:00:01:1d:dc:60:db:00:0c:29:d3:ac:77
message status code Success: "Release received."

Running an ifconfig will show that eth1 has no IP addresses set (except for its link-local address)

[email protected]:~$ ifconfig eth1
eth1      Link encap:Ethernet  HWaddr 00:0c:29:4f:26:c5  
          inet6 addr: fe80::20c:29ff:fe4f:26c5/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:3487 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1272 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:501952 (501.9 KB)  TX bytes:267192 (267.1 KB)

Now we can request addresses from DHCP server to bind the next available IP addresses to km-vm1 by using the command for IPv4 dhclient -v eth1 and for IPv6 dhclient -6 -v eth1 respectfully.

dhclient -v eth1dhclient -6 -v eth1
[email protected]:~$ sudo dhclient -v eth1
Internet Systems Consortium DHCP Client 4.2.4
Copyright 2004-2012 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on LPF/eth1/00:0c:29:4f:26:c5
Sending on   LPF/eth1/00:0c:29:4f:26:c5
Sending on   Socket/fallback
DHCPDISCOVER on eth1 to 255.255.255.255 port 67 interval 3 (xid=0x7cae5613)
DHCPREQUEST of 192.168.1.112 on eth1 to 255.255.255.255 port 67 (xid=0x1356ae7c)
DHCPOFFER of 192.168.1.112 from 192.168.1.2
DHCPACK of 192.168.1.112 from 192.168.1.2
bound to 192.168.1.112 -- renewal in 230 seconds.
[email protected]:~$ sudo dhclient -6 -v eth1
Internet Systems Consortium DHCP Client 4.2.4
Copyright 2004-2012 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Bound to *:546
Listening on Socket/eth1
Sending on   Socket/eth1
PRC: Soliciting for leases (INIT).
XMT: Forming Solicit, 0 ms elapsed.
XMT:  X-- IA_NA 29:4f:26:c5
XMT:  | X-- Request renew in  +3600
XMT:  | X-- Request rebind in +5400
XMT:  | X-- Request address 2001:192:168:1::111.
XMT:  | | X-- Request preferred in +7200
XMT:  | | X-- Request valid in     +10800
XMT: Solicit on eth1, interval 1050ms.
RCV: Advertise message on eth1 from fe80::20c:29ff:fed3:ac77.
RCV:  X-- IA_NA 29:4f:26:c5
RCV:  | X-- starts 1447710742
RCV:  | X-- t1 - renew  +0
RCV:  | X-- t2 - rebind +0
RCV:  | X-- [Options]
RCV:  | | X-- IAADDR 2001:192:168:1::111
RCV:  | | | X-- Preferred lifetime 7200.
RCV:  | | | X-- Max lifetime 43200.
RCV:  X-- Server ID: 00:01:00:01:1d:dc:60:db:00:0c:29:d3:ac:77
RCV:  Advertisement recorded.
PRC: Selecting best advertised lease.
PRC: Considering best lease.
PRC:  X-- Initial candidate 00:01:00:01:1d:dc:60:db:00:0c:29:d3:ac:77 (s: 153, p: 0).
XMT: Forming Request, 0 ms elapsed.
XMT:  X-- IA_NA 29:4f:26:c5
XMT:  | X-- Requested renew  +3600
XMT:  | X-- Requested rebind +5400
XMT:  | | X-- IAADDR 2001:192:168:1::111
XMT:  | | | X-- Preferred lifetime +7200
XMT:  | | | X-- Max lifetime +7500
XMT:  V IA_NA appended.
XMT: Request on eth1, interval 1040ms.
RCV: Reply message on eth1 from fe80::20c:29ff:fed3:ac77.
RCV:  X-- IA_NA 29:4f:26:c5
RCV:  | X-- starts 1447710744
RCV:  | X-- t1 - renew  +0
RCV:  | X-- t2 - rebind +0
RCV:  | X-- [Options]
RCV:  | | X-- IAADDR 2001:192:168:1::111
RCV:  | | | X-- Preferred lifetime 7200.
RCV:  | | | X-- Max lifetime 43200.
RCV:  X-- Server ID: 00:01:00:01:1d:dc:60:db:00:0c:29:d3:ac:77
PRC: Bound to lease 00:01:00:01:1d:dc:60:db:00:0c:29:d3:ac:77.

We can confirm by using ifconfig again:

[email protected]:~$ ifconfig eth1
eth1      Link encap:Ethernet  HWaddr 00:0c:29:4f:26:c5  
          inet addr:192.168.1.110  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: fe80::20c:29ff:fe4f:26c5/64 Scope:Link
          inet6 addr: 2001:192:168:1::111/64 Scope:Global
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:3647 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1365 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:519662 (519.6 KB)  TX bytes:292435 (292.4 KB)

And with that, we now have a Dual Stacked DHCP server! Although this looks quite straightforward, now I’ll tell you that it took me a few days to get understand and get the IPv6 side of things working as expected. There was plenty of googling, troubleshooting, screen staring and frustration with this one, but I have to give major props to a great page by Jochen Kirstätter on how the IPv6 side of install was done if I hadn’t have found it, I would still be poking in the dark *covers face*! You will find some great nuggets on Jochen’s blog here 🙂

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IPv6 and Junos – Stateless Address Autoconfiguration (SLAAC)

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From my research and testing, I’ve notice there are a few ways you can set IPv6 addresses to hosts. Essentially you have 3 methods; manually setting a Static IP address, Using Stateful Dynamic Address allocation via a DHCPv6 server, or by using Stateless Dynamic Address allocation. The first two methods are pretty standard as addressing with IPv4 is done this way however, the last method is new method that comes with IPv6 and this is actually known as Stateless Address Autoconfiguration (SLAAC). SLAAC, as its name suggestions, allows a host to auto configure itself without any manual intervention.

RFC4862 describe the SLAAC as

The IPv6 stateless autoconfiguration mechanism requires no manual configuration of hosts, minimal (if any) configuration of routers, and no additional servers. The stateless mechanism allows a host to generate its own addresses using a combination of locally available information and information advertised by routers. Routers advertise prefixes that identify the subnet(s) associated with a link, while hosts generate an “interface identifier” that uniquely identifies an interface on a subnet. An address is formed by combining the two. In the absence of routers, a host can only generate link-local addresses. However, link-local addresses are sufficient for allowing communication among nodes attached to the same link.

In essence, when using SLAAC to get the full 128-bit IPv6 address, it uses the 64-bit prefix that is advertised by the host or router for the first half, then in conjunction with the EUI-64 process, is able to allocation the second 64-bit of the address.

Note
The EUI-64 process in a nutshell, is the method of extending the 48-bit MAC Address and making it into a 64-bit value. This is done by splitting the 48-bit address into two 24-bit halves and adding the 16-bit hex value 0xFFFE in middle to create the last 64-bits

Configuring SLAAC

Enabling SLAAC with Junos is pretty straightforward. For my example, I’ve got an EX4200 connected to an Ubuntu 14.04LTS ESXi host in Vlan 200.

Before enabling the switch, the host’s interface has to be set to auto

[email protected]:~$ cat /etc/network/interfaces
{...}
# This is an autoconfigured IPv6 interface
iface eth0 inet6 auto

auto eth1
iface eth1 inet6 auto

Once that’s done, to make sure no address was learnt as I configured the switch, the interface was disabled using ifdown.

With the switch configuration, under the protocol router-advertisement stanza, the interface and the prefix (first 64-bits) that will be advertised need to be set. Additionally I enabled a traceoption to see the process from the switch’s perspective.

Interface ConfigurationEnabling SLAAC
{master:0}[edit]
[email protected]# show interfaces vlan unit 200 
family inet6 {
    address 2001:192:168:2::1/64;
}
{master:0}[edit protocols router-advertisement]
[email protected]# show 
traceoptions {
    file RA.log;
    flag all;
}
interface vlan.200 {
    prefix 2001:192:168:2::/64;
}

Verification

With that SLAAC has been enabled, simple isn’t it 🙂

Now, back on the host, I re-enabled the interface using ifup. By using ifconfig we can see that the IPv6 address has been auto configured onto the host.

[email protected]:~$ ifconfig -a eth1
eth1      Link encap:Ethernet  HWaddr 00:0c:29:4f:26:c5  
          inet addr:192.31.1.2  Bcast:192.31.1.255  Mask:255.255.255.0
          inet6 addr: 2001:192:168:2:20c:29ff:fe4f:26c5/64 Scope:Global
          inet6 addr: fe80::20c:29ff:fe4f:26c5/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:4 errors:0 dropped:0 overruns:0 frame:0
          TX packets:40 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:563 (563.0 B)  TX bytes:2334 (2.3 KB)

By looking closer at the ifconfig output, we can see how the EUI-64 process has been used to allocate the IPv6 address, as well as its link-local address:

eth1      Link encap:Ethernet  HWaddr 00:0c:29:4f:26:c5  
          inet6 addr: 2001:192:168:2:20c:29ff:fe4f:26c5/64 Scope:Global
          inet6 addr: fe80::20c:29ff:fe4f:26c5/64 Scope:Link

On the switch, by running the commands: show ipv6 neighbours, we can see the hosts’ link-local and SLAAC allocated addresses, both discovered by the Neighbour Discovery Protocol (NDP). And show ipv6 router-advertisement, which shows how many RA’s and RS’ have been sent and received by the switch.

IPv6 NeighborsRouter Advertisements
{master:0}
[email protected]> show ipv6 neighbors 
IPv6 Address                 Linklayer Address  State       Exp Rtr Secure Interface
2001:192:168:2:20c:29ff:fe4f:26c5
                             00:0c:29:4f:26:c5  stale       1110 no no      vlan.200    
fe80::20c:29ff:fe4f:26c5     00:0c:29:4f:26:c5  stale       1039 no no      vlan.200
{master:0}
[email protected]> show ipv6 router-advertisement 
Interface: vlan.200
  Advertisements sent: 4, last sent 00:04:45 ago
  Solicits received: 2, last received 00:04:46 ago
  Advertisements received: 0

When we look further at the traceoption, we can see the request from the host sent out Router Solicitation (RS) via its link-local address, to the destination of ff02::2 for the presence of routers (in this case a switch) on the link. The switch replies by sending a Router Advertisement (RA) to ff02::1 with the Router’s presence and link prefixes, MTU, and hop limits.

{Apr  7 06:29:13.002388 background dispatch running job ipv6_ra_delete_interface_config_job for task Router-Advertisement
Apr  7 06:29:13.002436 task_job_delete: delete background job ipv6_ra_delete_interface_config_job for task Router-Advertisement
Apr  7 06:29:13.002473 background dispatch completed job ipv6_ra_delete_interface_config_job for task Router-Advertisement
Apr  7 06:29:48.645889 ipv6_ra_receive_solicit: received solicit from fe80::20c:29ff:fe4f:26c5
Apr  7 06:29:48.646013 ipv6_ra_receive_solicit: task Router-Advertisement src fe80::20c:29ff:fe4f:26c5 dst ff02::2 hdr 0x26fc000 count 16 intf 0x283c0e8
Apr  7 06:29:48.646086 task_timer_reset: reset Router-Advertisement_ipv6ra
Apr  7 06:29:48.646137 task_timer_set_oneshot_latest: timer Router-Advertisement_ipv6ra interval set to 0.426219
Apr  7 06:29:49.073743 task_job_create_foreground: create job ipv6 ra for task Router-Advertisement
Apr  7 06:29:49.073857 foreground dispatch running job ipv6 ra for task Router-Advertisement
Apr  7 06:29:49.073978 ipv6_ra_send_advertisement: sending advertisement for ifl 73 to ff02::1
Apr  7 06:29:49.074018 (519322) sending advertisement for ifl 73
Apr  7 06:29:49.074106 	ifa 0x28383f0 2001:192:168:2::1/64
Apr  7 06:29:49.074942 	--> sent 56 bytes
Note
The ff02::1 and ff02::2 addresses are well-known IPv6 Multicast addresses that a host sends out to a RS, to all devices within the all-host multicast group for ff02::2, and for a router, the address ff02::1 is used to reply RS with RA. Although this process could be compared to the IPv4 broadcast address 255.255.255.255, its important to remember that broadcasts are not accepted by any IPv6 protocol.

SLAAC is a really useful way of easily enabling IPv6 across your network and let the host and devices auto configure themselves. In addition, as the EUI-64 process is key to SLAAC, as long as you keep a record of the MAC Addresses of each device, you’ll always be able to know what address goes with what device. Of course, there will be situations where Static or DHCP addressing will be more suitable however; if you need to quickly enable your network with IPv6 then SLAAC is the way to go!

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