AAA and VTYs in IOS-XR : Bingo

Continuing on the IOS-XR saga, this is the newest bunch of things that don't "work as expected" (© Cisco). Well, as expected by me, not by Cisco.

Everything started while trying to configure a primary and backup aaa login method on an ASR9k, when i realized that...

1) having a backup aaa login method with the same tacacs servers as the ones in the primary aaa login method (which is using the management vrf) doesn't work

Imagine the following aaa configuration:

!
tacacs source-interface MgmtEth0/RSP0/CPU0/0 vrf MGMT
tacacs source-interface Loopback0 vrf default
!
aaa group server tacacs+ TACACS-AAA-GROUP
 server x.x.x.x
 server y.y.y.y
!
aaa group server tacacs+ TACACS-VRF-AAA-GROUP
 server x.x.x.x
 server y.y.y.y
 vrf MGMT
!
aaa authentication login default group TACACS-VRF-AAA-GROUP group TACACS-AAA-GROUP local
!

This is supposed to work in the following way:

As long as at least one mgmt interface is up (i'm using a virtual-ip for the mgmt interfaces), tacacs communication should happen through the out-of-band mgmt interfaces. If all mgmt interfaces are down, then tacacs communication should happen through an inband interface.

Guess what! There seems to be an issue with the above scenario, because in the 2nd case (where all mgmt interfaces are down) tacacs communication doesn't happen at all. Looking at the debugs, it's like the router isn't even trying to use the second (global) tacacs group. This has already been opened as SR (according to tac this should work, so let's hope it's just a bug), so i'm waiting for developers' feedback right now.

In order to overcome the above problem, i thought of using different vty templates, each one with a different access method.

In IOS you can have the following vty configuration and then access vtys 11-15 by either using "telnet x.x.x.x 3001" or "telnet x.x.x.x 2000+y" where y is the tty number displayed by using the command "show line".

!
line vty 11 15
 login authentication BACKUP-AAA
 rotary 1
!

Since the "rotary" command is not supported in IOS-XR, this is what you can do:

!
line default
 login authentication default
!
line template VTY-TEMPLATE
 login authentication BACKUP-AAA
!	
vty-pool default 0 10
vty-pool VTY-POOL 11 20 line-template VTY-TEMPLATE
!

And this is the point you realize that you can't choose a vty, because...

2) specific vtys can be accessed only through a combination of a line template and a specific ACL

First shock: You cannot easily access a specific vty line in IOS-XR. Vtys in IOS-XR work in a very different way in comparison to the IOS ones. According to the BU, when you do a telnet/ssh to the router, the router starts a scanning from the first vty (0) to the last vty (including all custom configured ones). When a free (available) vty is found, the vty ACL is checked in order to verify whether its permit conditions are met. If the vty ACL allows this specific access, then the session is opened.

Second shock: If the vty ACL doesn't allow access, then scanning for free vtys continues until one vty is found that has an ACL that allows this specific access. So, the only to way to access a specific vty is to apply a specific and unique ACL under that vty that allows your i.e. source ip. In order to access another vty, you'll have to use another source ip, and so on. Still wondering why Cisco chose such an implementation.

So i tried the following:

!
line default
 login authentication default
 access-class ingress HOST1-ACL
 transport input telnet ssh
!
line template LINE-TEMPLATE
 login authentication BACKUP-AAA
 access-class ingress HOST2-ACL
 transport input telnet ssh
!
vty-pool default 0 10
vty-pool VTY-POOL 11 20 line-template LINE-TEMPLATE
!
ipv4 access-list HOST1-ACL
 10 permit ipv4 host x.x.x.x any
 20 deny ipv4 any any log
!
ipv4 access-list HOST2-ACL
 10 permit ipv4 host y.y.y.y any
 20 deny ipv4 any any log
!

...and this is what i got when i tried to telnet from HOST2 to the router

HOST2$ telnet router
Trying z.z.z.z...
Connected to router.
Escape character is '^]'.
Connection to router closed by foreign host.

ipv4_acl_mgr[267]: %ACL-IPV4_ACL-6-IPACCESSLOGP : access-list HOST1-ACL (20) deny tcp y.y.y.y(46387) -> z.z.z.z(23), 1 packet

So i didn't manage to telnet into vtys 11-20, because my telnet session was dropped by HOST1-ACL. Is this another bug? Who knows...

And when i thought i had met every possible issue, i also found out that vty ACLs are useless for ssh sessions, because...

3) ssh sessions get established before hitting the vty ACLs

Yeap, that's another shock (3rd in a row). When you do a ssh session to an IOS-XR router, the vty (the one that the ssh session will use) is consumed regardless of your vty ACL. That means that the vty is occupied during the whole time the router is waiting for you to enter your password. It's only after you enter your password that you get disconnected because of the vty ACL. And that's a nice way to dos attack an IOS-XR router.

%SECURITY-SSHD-6-INFO_GENERAL : Incoming SSH session rate limit exceeded
%SECURITY-SSHD-3-ERR_GENERAL : Failed to allocate pty

Note: the same happens with telnet, but since the username is asked after the ACL check, the time while telnet session remains open is limited.

But wait; isn't that supposed to be solved by Management Plane Protection (MPP)? Sure it is, but...

4) MMP configuration doesn't support ACLs

Who would have though of that! MPP configuration expects you to configure hosts and networks in a Juniper kind of way (although Juniper allows you to reuse the "clients" section).

RP/0/RSP0/CPU0:router(config-telnet-peer)#address ipv4 ?
  A.B.C.D         Enter IPv4 address
  A.B.C.D/length  Enter IPv4 address with prefix

RP/0/RSP0/CPU0:router(config-telnet-peer)#address ipv6 ?
  X:X::X         Enter IPv6 address
  X:X::X/length  Enter IPv6 address with prefix

So, if you happen to have already defined ACLs for your NMS/OSS/whatever, which are already being used somewhere else, you can't reuse those ones, but you have to reconfigure all hosts and networks under the MPP section (something that makes mass router config changes even more difficult). You can't even reuse the same hosts/networks under different interfaces!

!
control-plane
 management-plane
  inband
   !
   interface GigabitEthernet0/3/0/0
    allow SSH peer
     address ipv6 2001:db8::69/64
    !
   !
   interface GigabitEthernet0/3/0/1
    allow SSH peer
     address ipv6 2001:db8::69/64
    !
   !

And that's surely a nice way to further "expand" your configuration (not to mention BGP dynamic neighbors that are not supported either, but's that's another story).


That's 4 in a row Cisco. Bingo!!!

Note: Many thanks to Arie for helping me with the 2nd issue (once again).


Question to the public:

Is there a character in IOS-XR that fully resembles "!" as a starting comment indicator, like in IOS?

IOS

router(config-line)#login authentication BACKUP-AAA ! backup
router(config-line)#

IOS-XR

RP/0/RSP0/CPU0:router(config-line)#login authentication BACKUP-AAA ! backup
                                                                   ^
% Invalid input detected at '^' marker.

In IOS-XR, "!" works only when it is the first character in the line.

Debugging IPv6 MTU issues in Windows

A common problem you might face soon (World IPv6 Day is 5 days away) is reachability to IPv6 sites due to MTU issues. ICMPv6 has a nice internal mechanism which is supposed to help the application overcome these issues, but like in the IPv4 world, not everything is perfect.

Let's suppose that an IPv6 subscriber is using a DSL router and is connected through PPPoE to a BRAS.

TARGET <=> BRAS <=> DSL-ROUTER <=> HOST

The usual MTU for PPPoE connections is 1492 bytes, as shown below.

1500 bytes = Ethernet Payload
-     6 bytes = PPPoE header
-     2 bytes = PPP ID
---------------------------------
1492 bytes = IPv6 Packet that can be carried over a PPPoE connection

If your host is configured with 1492 (or something lower) as MTU on its LAN interface, then the OS running on it will automatically take care of "fragmentation", so you don't need to worry for anything. Unfortunately this isn't a common scenario by default. You either have to configure it manually on the host or if you are lucky enough and the DSL modem supports advertisement of MTU to its LAN interface through RA messages (and your host accepts them), it will happen automatically.

If your host is configured with anything larger than 1492 on its LAN interface (in most cases it's the default of 1500), problems might arise.

Users with hosts running Windows can try to ping an IPv6 address (i.e. the next hop after the DSL router) in order to find possible issues with the MTU. The closer the target is, the easier it will be to troubleshoot the problem. Then you start moving towards the target until you meet the issue.

First, some numbers you will need regarding the various headers

1492 bytes = IPv6 Packet
-  40 bytes = IPv6 Header
-   8 bytes = ICMPv6 Header
-------------------------------
1444 bytes = ICMPv6 payload data

Since Windows ping uses the actual payload as a size, if you want to send a total of 1492 bytes, you have to send 1492-40-8=1444 bytes of ICMPv6 payload data. Anything larger will lead to either a problem or to fragmentation.

Windows>ping -l 1444 x:x::x

Pinging target [x:x:xx] with 1444 bytes of data:

Reply from x:x:xx: time=53ms
Reply from x:x:xx: time=51ms
Reply from x:x:xx: time=54ms
Reply from x:x:xx: time=53ms

Ping statistics for x:x:xx:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 51ms, Maximum = 54ms, Average = 52ms

These are the relevant Wireshark captures.

The ICMP conversation between all involved devices

1444 bytes ICMP request from HOST to TARGET

If you increase the above number, you'd better start looking for "Too big" ICMPv6 received messages from any hop towards the target, otherwise you are in trouble.

i.e. if you ping with 1446 bytes of data, you get the following:

Windows>ping -l 1446 x:x:xx

Pinging target [x:x:xx] with 1446 bytes of data:

Packet needs to be fragmented but DF set.
Reply from x:x:xx: time=53ms
Reply from x:x:xx: time=55ms
Reply from x:x:xx: time=57ms

Ping statistics for x:x:xx:
    Packets: Sent = 4, Received = 3, Lost = 1 (25% loss),
Approximate round trip times in milli-seconds:
    Minimum = 53ms, Maximum = 57ms, Average = 55ms

These are the relevant Wireshark captures.

The ICMP conversation between all involved devices (fragmentation included))

1446 bytes ICMP request from HOST to TARGET

ICMP reply ("Too big") from DSL-ROUTER to HOST (original truncated message included)

As you can see, device DSL-ROUTER is replying with "Too Big" message in the first packet to the HOST and informs it about the MTU (1492) supported in the next-hop link (see RFC 4443 for ICMPv6 info); that's the WAN link towards the BRAS, where PPPoE is running on.

If you are in the unfortunate position to not get any incoming packets, you can safely assume (if everything else is fine) that someone in the path is blocking ICMPv6 messages.

The reply message is exactly 1280 bytes, which is the minimum packet size IPv6 supports. This leads to the original message being truncated in the reply message to 1280-40=1240 bytes for the ICMPv6 packet or  1240-8-40-8=1184 bytes for the actual payload data. So you loose 1446-1184=262 bytes of payload data in the reply message.

Next packets get a successful answer from the target, because they are sent as fragmented (1432+14 bytes).

1432 bytes ICMP request from HOST to TARGET

14 bytes ICMP request from HOST to TARGET

Windows is "smart" enough to keep track of this status for some minutes (in the so called destination or route cache), so next time you send large packets, the first packet is not lost, because fragmentation happens right away.

Windows>ping -l 1446 x:x:xx

Pinging target [x:x:xx] with 1446 bytes of data:

Reply from x:x:xx: time=54ms
Reply from x:x:xx: time=53ms
Reply from x:x:xx: time=55ms
Reply from x:x:xx: time=52ms

Ping statistics for x:x:xx:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 52ms, Maximum = 55ms, Average = 53ms

Imho, it's better to make your host use the appropriate MTU from the beginning (i.e. hardcode 1492 or use RA's value) and not depend on ICMPv6 messages to do fragmentation. Some people have proposed to always use the minimum of 1280 (Geoff Huston, Tore Anderson), in order to be safe on every possible case (tunnels involved). I generally prefer to use the maximum possible, hoping that someone in the middle won't mess with ICMPv6 messages. I know that currently this is not the case (so stick with something lower, like 1280, for now), but this will probably change as native IPv6 gets deployed. Unless we start filtering ICMPv6 messages uncontrollably...like many do on IPv4. Does "Internet Control Message Protocol" say anything to you?

Notes

1) RFC 1982 describes Path MTU Discovery (PMTUD) for IPv6.
2) RFC 4821 will help a lot in PMTUD, when and if all vendors start implementing it.
3) In order to see clearly the fragmented IPv6 packets in Wireshark, you have to disable reassembly in preferences.
4) You can use the commands "ipv6 rc" and "ipv6 rcf" in order to view and clear the destination/route cache in WindowsXP

To forward, to peer, or to tunnel?

In an imaginary Cisco world every device would be able to talk with every other device in various layers. In the actual Cisco world, some devices can talk to some devices, while they can't talk to some other devices.

I'm talking specifically about L2 Control Protocols (L2CPs), when these need to be exchanged between different devices in order to support a requirement (i.e. create a spanning-tree loop). Cisco's L2 Protocol Tunneling (L2PT) can help in accomplishing some of these cases.

So let's suppose you have a scenario like the following.

When using the simplest form of devices (L2 switches like 3750), you can just tunnel the L2CPs between devices S1 and S2 and everything will be fine. Spanning tree running on devices C1-C4 will see a loop and will block a port depending on various parameters (priority, cost, etc).

As you move ahead and start to replace the S1 or S2 device with another (usually better), you realize that the new device supports a different way of handling L2CPs, which might be "incompatible" with the old way.

Generally, you can do the following actions on L2CPs as they enter a port:

forward: frame is forwarded to another device without any change (no local processing takes place)
drop: frame is dropped
peer: frame is processed/terminated locally
tunnel: frame is tunneled to another device after changing the destination mac address (L2PT)

Tunneling is quite common is scenarios like the above, where you need to pass the L2 frame across a L2 domain, without having the intermediate devices act upon it.

You can also achieve the same result with forwarding, as long as you don't have a native L2 domain in between, because you might end up mixing local protocols with protocols that just pass over.

It's obvious that you cannot have tunneling on one side and forwarding on the other side, because exchanged frames won't be able to "talk" each other. i.e. for STP one side will tunnel the frame by changing the destination mac address from 01-00-0c-cc-cc-cd (or 01-80-c2-00-00-00) to 01-00-0c-cd-cd-d0, while the other side will just forward the frame by keeping the original destination address of 01-00-0c-cc-cc-cd (or 01-80-c2-00-00-00).

Below you'll find a list with all available options regarding the handling of L2CPs on some known platforms:

Device	Interface	forward	drop	peer	tunnel
3750	L2 switchport				l2protocol-tunnel
ME-3400	L2 switchport				l2protocol-tunnel
ME-3800X	L2 switchport		l2protocol drop	l2protocol peer
ME-3800X	L2 service instance	l2protocol forward (1)		l2protocol peer	l2protocol tunnel
7600/67xx	L2 switchport				l2protocol-tunnel
7600/ES	L2 switchport				l2protocol-tunnel
7600/ES	L3		l2protocol drop	l2protocol peer
7600/ES	L3 service instance	l2protocol forward
ASR9000	L2 transport	by default (2)			l2protocol tunnel

As you can see, you cannot have L2 communication between a service instance on a 7600/ES and one of the smaller platforms, because 7600/ES doesn't support tunneling and the smaller platforms do not support forwarding. Actually, the biggest surprise to me was the lack of support of L2PT on the 7600 with the ES cards when using service instances. I had the impression that this would be the most feature rich platform.

Cisco's proposal is to use the same platform for such scenarios, because they haven't verified anything else and some platforms were built to be used in specific ways. So instead of supporting the same feature (L2PT was their idea after all) along the range of platforms, you should always replace them in pairs. And if by accident, you happen to have more S devices serving many overlapping rings, then you have to replace all of them.

I would prefer, instead of promoting new platforms or new designs, to focus on fixing the existing platforms, so they can cooperate with each other. After all, if a platform is good enough, it will get its share in the market.

Also, the online documentation is quite incomplete on this area. You have to guess what will happen in most cases. We had to open 3 different cases and involve our account team in order to clarify things and push for fixing the documentation. Not surprisingly enough, the peering functionality is another mess. I'll probably need to write another post describing all available options (which lead to different behavior) on these platforms.


Notes

1) "l2protocol forward" on ME-3800X will become available in the next major release. Thanks to Cisco for giving.us the chance to try it earlier.
2) This is the default behavior according to Xander's doc here.
3) Arie asked me to add some extra information about PW/MST/REP/PVST-AG (and all these L2 HA) scenarios. I'll try to write a new post as soon as i find enough free time to test them.

How Multi is MP-BGP in IOS-XR?

This caught me on surprise. I had an impression that IOS-XR as an advanced operating system would support all kinds of multi-protocol transferability over BGP.

As it seems, there is an issue when transferring IPv6 prefixes over an IPv4 peering or IPv4 prefixes over an IPv6 peering. This happens for sure on ASR9k running latest 4.1.0, but i haven't verified it on the CRS yet.

IPv4 prefixes over IPv6 peering
This doesn't seem to be supported based on the available configuration options.
What is even more worrying, is that no other address family is supported too.

RP/0/RSP0/CPU0:ASR#conf t
RP/0/RSP0/CPU0:ASR(config)#router bgp 100
RP/0/RSP0/CPU0:ASR(config-bgp)#neighbor 2001::1:2:3
RP/0/RSP0/CPU0:ASR(config-bgp-nbr)#address-family ?
  ipv6  IPv6 Address Family

IPv6 prefixes over IPv4 peering
This is supported according to the configuration options, but it doesn't work.
Cisco also insists that this is definitely supported.

RP/0/RSP0/CPU0:ASR#conf t
RP/0/RSP0/CPU0:ASR(config)#router bgp 100
RP/0/RSP0/CPU0:ASR(config-bgp)#neighbor 10.11.254.37
RP/0/RSP0/CPU0:ASR(config-bgp-nbr)#address-family ?
  ipv4   IPv4 Address Family
  ipv6   IPv6 Address Family
  l2vpn  L2VPN Address Family
  vpnv4  VPNv4 Address Family
  vpnv6  VPNv6 Address Family

As soon as you enable the IPv6 address family under the IPv4 neighbor, the BGP session is dropped and it never comes up.

RP/0/RSP0/CPU0:ASR#sh bgp sum
BGP router identifier 10.11.254.38, local AS number 100
BGP generic scan interval 60 secs
BGP table state: Active
Table ID: 0xe0000000   RD version: 1
BGP main routing table version 1
BGP scan interval 60 secs

BGP is operating in STANDALONE mode.


Process       RcvTblVer   bRIB/RIB   LabelVer  ImportVer  SendTblVer  StandbyVer
Speaker               1          1          1          1           1           1

Neighbor        Spk    AS MsgRcvd MsgSent   TblVer  InQ OutQ  Up/Down  St/PfxRcd
10.11.254.37      0  100        0       0        0    0    0 00:00:00 Idle

Also, debug shows that there are no tries of BGP to establish a session. It's like BGP gets disabled.

The only doc that refers such a limitation (in IOS-XR 3.3 for CRS) is the one in http://www.cisco.com/en/US/docs/ios_xr_sw/iosxr_r3.3/conversion/reference/guide/cn33main.html#wp1028960

A given address family is only supported with a neighbor whose address is from that address family. For instance, IPv4 neighbors support IPv4 unicast and multicast address families, and IPv6 neighbors support IPv6 unicast and multicast address families. However, you cannot exchange IPv6 routing information with an IPv4 neighbor and vice versa.

I searched all CCO for more information, but i didn't manage to find something useful. Does anyone have extra information to share? TAC is struggling (as usual) to find an answer...

Update #1
Cisco verified once more that this is a supported configuration. Arie Vayner (and later tac) proposed to add an IPv6 address to the interface being used as an IPv4 next-hop. Indeed, this solved the problem and the BGP session came up. But then it became even more interesting...

Two IPv6 prefixes are learned from the IPv4 neighbor. Next-hop is an IPv6 address.

RP/0/RSP0/CPU0:ASR#sh bgp ipv6 uni 
BGP router identifier 10.11.254.38, local AS number 100
BGP generic scan interval 60 secs
BGP table state: Active
Table ID: 0xe0800000   RD version: 5
BGP main routing table version 5
BGP scan interval 60 secs

Status codes: s suppressed, d damped, h history, * valid, > best
i - internal, r RIB-failure, S stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network            Next Hop            Metric LocPrf Weight Path
* i2001::1:2:3/128    2003::1:2:3              0    100      0 ?
* i2003::/64          2003::1:2:3              0    100      0 ?

Processed 2 prefixes, 2 paths

If i remove the IPv6 address from the interface that is being used as next-hop (the one i added before), then i automatically get an IPv6 prefix with an IPv4 next-hop!!!

RP/0/RSP0/CPU0:core-distr-kln-02#sh bgp ipv6 uni 
BGP router identifier 10.11.254.38, local AS number 100
BGP generic scan interval 60 secs
BGP table state: Active
Table ID: 0xe0800000   RD version: 6
BGP main routing table version 6
BGP scan interval 60 secs

Status codes: s suppressed, d damped, h history, * valid, > best
i - internal, r RIB-failure, S stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network            Next Hop            Metric LocPrf Weight Path
*>i2001::1:2:3/128    10.11.254.41             0    100      0 ?

Processed 1 prefixes, 1 paths

The BGP session stays up, until something happens that will reset it. Then it will stay down forever, as it was happening in the beginning.

I must say that i cannot endorse such an implementation. Using exactly the same configuration, you get different results, depending on the order of (un)configuring things. Also, i cannot understand why the establishment of an IPv4 BGP session that is going to negotiate IPv4/IPv6 address-family capabilities should depend on whether an IPv6 next-hop exists or not. That should be left for the NLRI exchange routine.

After all, RFC 4271 defines among others two error conditions for the NEXT_HOP attribute:

If the NEXT_HOP attribute field is syntactically incorrect, then the Error Subcode MUST be set to Invalid NEXT_HOP Attribute. The Data field MUST contain the incorrect attribute (type, length, and value). Syntactic correctness means that the NEXT_HOP attribute represents a valid IP host address.

If the NEXT_HOP attribute is semantically incorrect, the error SHOULD be logged, and the route SHOULD be ignored. In this case, a NOTIFICATION message SHOULD NOT be sent, and the connection SHOULD NOT be closed.


Update #2
After the developers got involved, we ended up with the following:

1. In IOS-XR you need an IPv6 NH in order to activate the IPv6 AF for an IPv4 BGP session.
2. If you don't have an IPv6 NH, then the IPv4 BGP session won't even come up.
3. The above was done to protect against misconfiguration, because otherwise you would get a misleading v4 mapped v6 address as NH.
4. If you have an IPv6 NH, then the IPv4 BGP session with the IPv6 AF will come up.
5. If afterwards you remove the IPv6 NH, then the session deliberately remains up and you get a misleading v4 mapped v6 address as NH.

Cisco agreed (thx Xander) that the behavior in 3 and 5 contradict each other, so a short-term solution (update the documentation and print a warning message) got recorded in CSCtq26829.

BRAS/Server initiated renewal for DHCPv6-PD leases - When?

One major issue when dealing with IPv6 CPEs is the currently missing capability to renew automatically the IPv6 addresses on the CPE's LAN after a disconnect/reconnect of the subscriber's dynamic session.

Although there are some tricks (#1, #2) for client (subscriber) initiated renewal, not all CPE vendors support those tricks. Also many times it is preferable to have the BRAS/BNG, or generally the ISPs, control this renewal, since all the AAA (and BSS/OSS) systems are usually managed by them.

The DHCPv6 "Reconfigure" message was made to help in the above case. According to RFC 3315:

RECONFIGURE (10) A server sends a Reconfigure message to a client to inform the client that the server has new or updated configuration parameters, and that the client is to initiate a Renew/Reply or Information-request/Reply transaction with the server in order to receive the updated information.
...
The client includes a Reconfigure Accept option if the client is willing to accept Reconfigure messages from the server.

It's obvious that without this support, a client must wait until it renews its lease to get configuration updates, which might be from some hours to many days. Btw, shouldn't the change of the WAN interface state on the CPE automatically cause the renewal of the delegated prefix on its LAN???

Also, according to the recently approved informational RFC 6204, the support of the DHCPv6 Reconfigure option is a MUST for IPv6 CPEs.

WAA-4: The IPv6 CE router MUST be able to support the following DHCPv6 options: IA_NA, Reconfigure Accept and DNS_SERVERS.

Now, someone malicious might translate the above "MUST be able to support" phrase into "ok, it's not actually required to support it now, but you must be able to support it in the future". It definitely would be better to have it as "MUST support".

A recent "IPv6 CE Router Interoperability Whitepaper" from UNH-IOL shows that none of the CPEs that were tested, supported this option.

The last issue discovered during the testing was IPv6 CE router lack of support for DHCP Reconfigure. According to draft-ietf-v6ops-ipv6-cpe-router-09, “WAA-4: The IPv6 CE router MUST be able to support the following DHCPv6 options: IA_NA, Reconfigure Accept [RFC3315], DNS_SERVERS [RFC3646].” Therefore the IPv6 CE routers should have included the Reconfigure Accept in DHCPv6 Request or Solicit messages.

It gets a little bit more complicated, if you check what RFC 3633 says about the "Reconfigure" message when it is used for Prefix Delegation:

13.1. Delegating Router behavior

The delegating router initiates a configuration message exchange with a requesting router, as described in section 19, "DHCP Server-Initiated Configuration Exchange" of RFC 3315, by sending a Reconfigure message (acting as a DHCP server) to the requesting router, as described in section 19.1, "Server Behavior" of RFC 3315. The delegating router specifies the IA_PD option in the Option Request option to cause the requesting router to include an IA_PD option to obtain new information about delegated prefix(es).

13.2. Requesting Router behavior

The requesting router responds to a Reconfigure message, acting as a DHCP client, received from a delegating router as described in section 19.4, "Client Behavior" of RFC 3315. The requesting router MUST include the IA_PD Prefix option(s) (in an IA_PD option) for prefix(es) that have been delegated to the requesting router by the delegating router from which the Reconfigure message was received.

So, if someone claims support of the "Reconfigure" option, where does it refer to? DHCPv6 or DHCPv6-PD? What about Relay?

On the server side, Juniper MX series already support it (it's called "dynamic reconfiguration for DHCPv6"), but Cisco ASR1k doesn't. Cisco CNR 7.x also supports it, so does (or will) Dibbler 0.8.0. ISC DHCPv6 server and Windows Server 2008 probably don't.

Notes

• Our experience with IPv6 CPEs until now is disappointing on this matter. Although we have feedback from various CPE vendors that they will support it, none of them actually supports it now.
• Wouldn't it be interesting to have the "Reconfigure" message be sent by the BRAS/BNG DHCPv6 server to the client, when the router receives a Radius CoA (RFC 3576) packet for this specific subscriber?