Category: IPv6

We all know that IPv6 handles host network parameter initialization a bit different than IPv4 (where we usually use DHCP), but the details could still confuse you if you’re just entering the IPv6 world.

A typical LAN-attached hosts needs its own address as well as the addresses of the default router and DNS server. DHCPv4 provides all three; in the IPv6 world you need two or three protocols as summarized in the following table

If you want your network to remain multihomed when the Internet migrates to IPv6, you need your own Provider Independent (PI) IPv6 prefix. That’s old news (I was writing about the multihoming elephant almost two years ago), but most of the IT industry managed to look the other way pretending the problem does not exist. It was always very clear that the lack of other multihoming mechanisms will result in explosion of global IPv6 routing tables (attendees of my Upcoming Internet Challenges webinar probably remember the topic very well, as it was one of my focal points) and yet nothing was done about it (apart from the LISP development efforts, which will still take a while before being globally deployed).

To make matters worse, some Service Providers behave like the model citizens in the IPv6 world and filter prefixes longer than /32 when they belong to the Provider Assigned (PA) address space, which means that you cannot implement reliable multihoming at all if you don’t get a chunk of PI address space.

Last week I ran numerous lab tests while preparing router configurations for the Building IPv6 Service Provider Core webinar. One of the fantastic test results: DHCPv6 relaying works correctly on a 7200 running 12.2(33)SRE2, even when the client requests IA_PD option.

A while ago I wrote about IPv6 addressing challenges some ISPs face and recommended what I thought was agreed-upon practice of giving residential customers a /64 or a /56. Not long after, I received an e-mail from an IPv6 guru saying:

[Worse] is when people start claiming to have expertise in IPv6 and promulgate this idea of residential /56s and /64s as immutable fact. The reality is that it is becoming more and more apparent that /56s and especially /64s to residential customers are going to be harmful to future innovation in IPv6.

When IESG decided to adopt SIP, not TUBA (TCP/UDP over CLNP) as IPv6, a lot of people were mightily disappointed and some of them still propagate the myths how CLNP with its per-node addresses would fare better than IPv6 with its per-interface addresses (you might find the writings of John Day on this topic interesting and Petr Lapukhov is also advocating this view in his comments).

These views are correct when considering small-scale (intra-network) multihoming, but unfortunately wrong when it comes to Internet-scale multihoming, where CLNP with TCP on top of it would be as bad as IPv4 or IPv6 is (routing table explosion due to multihoming is also one of the topics of my Upcoming Internet Challenges webinar).

Paulie, a frustrated enterprise IPv6 early adopter summarized his pains in a comment to my “Small-site multihoming in IPv6: mission impossible?” post saying “[IPv6/IPv6 support] is a mess and depressing” and asked “Is it too late to go to CLNS?”

Quite a few old-timers (I’m definitely one of them) lament the glory days of VMS, DECnet Phase V and CLNP, but while CLNP was a viable alternative for the next-generation IP in 1993, it would fare worse than IPv6 today.

Summary: I can’t figure out how to make small-site multihoming (without BGP or PI address space) work reliably and decently fast (failover in seconds, not hours) with IPv6. I’m probably not alone.

Problem: There are cases where a small site needs (or wants) to have Internet connectivity from two ISPs without going through the hassle of getting a BGP AS number and provider-independent address space, and running BGP with both upstream ISPs.

Greg Ferro reached an interesting conclusion after going through my Content over IPv6 presentation: we won’t see IPv6 for a few years, so why bother. Although I disagree with his approach, he may be right ... but if you decide to ignore IPv6, you might be forced to implement it in a hurry, at which point you’ll be stuck if your equipment won’t support IPv6. The very minimum you need to do today is to buy IPv6-ready gear (and yell at the vendors if they try to charge extra for IPv6 support).

One of the comments to my “IPv6 in Data Center: after a year, Cisco is still not ready” post included the following facts:

Up through at least 15.0(1)M and 12.2(53)SE2 the IPv6 support for management protocols is spotty; syslog is there, SNMP traps and the RADIUS/TACACS control plane aren't.

Another bug along the same lines was discovered by Jónatan Jónasson: When the Cisco IOS Login Enhancements feature logs successful or failed login attempt, it reports the top 32 bits of the remote IPv6 address in IPv4 address format. Here’s a sample printout taken from a router running IOS release 15.0(1)M.

P#
%SEC_LOGIN-5-LOGIN_SUCCESS: Login Success [user: test] 
[Source: 254.192.0.0] [localport: 23] at ...
P#who
    Line       User       Host(s)              Idle       Location
*  0 con 0                idle                 00:00:00   
   2 vty 0     test       idle                 00:00:06 FEC0::CCCC:1

It looks like the recommendation we’ve been making two years ago is still valid: use IPv4 for network management.

Yesterday I spent the whole day at another fantastic IPv6 Summit organized by Jan Žorž of the go6 institute. He managed to get two networking legends: Patrik Fältström (he was, among numerous other things, a member of Internet Architecture Board) had the keynote speech (starts @ 11:40) and Daniel Karrenberg (of the RIPE fame) was chairing the technical panel discussion. My small contribution was a half-hour talk on the importance of IPv6-enabled content (starts @ 37:00).

Today I’m delivering another IPv6 presentation, this time at the 4th Slovenian IPv6 Summit organized by tireless Jan Žorž from the go6 Slovenian IPv6 initiative. It’s thus just the right time to review the post I wrote a bit more than a year ago about lack of IPv6 readiness in Cisco’s Data Center products. Let’s see what has changed in a year:

Just stumbled across this unbelievable fact in the Nexus 1000V release notes:

IPV6 ACL rules are not supported.

My first reaction: “You must be kidding, right? Are we still in 20th century?” ... and then it dawned on me: Nexus 1000V is using the NX-OS control plane and it’s still stuck in 4.0 release which did not support IPv6 ACLs (IPv6 support was added to NX-OS in release 4.1(2)).

Mike was wondering whether his ISP is giving him what he needs to start an IPv6 pilot within his enterprise network. He wrote:

So I got an IPv6 assignment with a /120 mask (basically our IPv4/24 network mapped to IPv6) and two smaller networks to use for links between our external router and the ISP.

Dear Mike’s ISP: where were you when the rest of the world was preparing to deploy IPv6? Did you read IPv6 Unicast Address Assignment Considerations (RFC 5375) or IPv6 Address Allocation and Assignment Policy from RIPE or your regional registry?

My DHCPv6+PPPoE post received a very comprehensive comment from Ole Troan (thank you!) in which he explains the context in which DHCPv6 was developed (a mechanism to give a static IPv6 prefix to a customer) and its intended usage (as the prefix is static, it should have a very long lifetime).

However, when you deploy DHCPv6 in some modern access networks (it’s not just PPPoE, Carrier Ethernet fares no better), you might experience subtle problems. Let’s start with a step-by-step description of how DHCPv6 works:

Every time someone throws me an IPv6 curveball, I’m surprised when I discover another huge can of worms (I guess I should have learned by now). This time it started pretty innocently with a seemingly simple PPPoE question:

What happens if an ISP decides to assign dynamic IPv6 subnets? With static assignment, the whole stuff is pretty straight-forward due to ND, RA & DHCPv6, but if dynamic addresses are used, what happens if the subnet changes - how will the change be propagated to the end-user devices? The whole thing is no problem today due to the usage of NAT / PAT...

LAN address allocation with changing DHCPv6 prefix is definitely a major problem, but didn’t seem insurmountable. After all, you can tweak RA timers on the LAN interface, so even though the prefix delegated through DHCPv6 would change, the LAN clients would pick up the change pretty quickly. WRONG ... at least if you use Cisco IOS.