Finally: native IPv6 at home!

▼ It took a while, but I finally got native IPv6 at home from Ziggo, my cable ISP a few months ago. All it took was a new cable modem / home router, because they don't support IPv6 on the one I've had since I signed up with them six years ago. And lo and behold: I got myself some IPv6:

$ ifconfig en0
en0: flags=8863 mtu 1500
  ether xx:xx:xx:xx:xx:xx 
  inet6 fe80::8d:5a:e4d:176f%en0 prefixlen 64 secured scopeid 0x8 
  inet 192.168.78.24 netmask 0xffffff00 broadcast 192.168.78.255
  inet6 2001:1c00:d00:7300:xxxx:xxxx:xxxx:xxxx prefixlen 64 autoconf secured 
  inet6 2001:1c00:d00:7300:75bf:1d31:ac76:d080 prefixlen 64 autoconf temporary 
  nd6 options=201
  media: autoselect
  status: active

Although it doesn't say so anywhere on the management interface of the cable modem, it looks like I got a /56 prefix (2001:1c00:d00:7300::/56) from Ziggo.

My understanding is that Ziggo only supports IPv6 with the modem in router mode, so the cable modem acts as a NAT router.

So I wondered: what if I also let my Apple Time Machine act as a router, behind Ziggo's modem/router? I told the Time Machine to configure IPv6 automatically and IPv6 mode native, and this is what happened:

(By the way, does anyone know what "Enable IPv6 Connection Sharing" does? I get the same IPv6 addresses on my computer, it's just that the Airport Utility shows a little less information. In any event, on my Mac I get:

$ ifconfig en0
en0: flags=8863 mtu 1500
  ether xx:xx:xx:xx:xx:xx 
  inet6 fe80::8d:5a:e4d:176f%en0 prefixlen 64 secured scopeid 0x8 
  inet 192.168.78.24 netmask 0xffffff00 broadcast 192.168.78.255
  inet6 2001:1c00:d00:73f0:xxxx:xxxx:xxxx:xxxx prefixlen 64 autoconf secured 
  inet6 2001:1c00:d00:73f0:7ccf:266b:8f69:4f46 prefixlen 64 autoconf temporary 
  nd6 options=201
  media: autoselect
  status: active

So either Ziggo / the Ziggo modem delegated a /60 out of the /56 given to the modem. On my regular network, the Time Capsule used the first /64 out of that /60. On the guest network, it uses the second /64:

vlan0: flags=8843 mtu 1500
  options=23
  ether xx:xx:xx:xx:xx:xx
  inet6 fe80::21b:63ff:fe95:7d9b%vlan0 prefixlen 64 scopeid 0x7 
  inet 172.16.42.23 netmask 0xffffff00 broadcast 172.16.42.255
  inet6 2001:1c00:d00:73f1:xxxx:xxff:fexx:xxxx prefixlen 64 autoconf 
  inet6 2001:1c00:d00:73f1:2c25:ea92:9deb:d27f prefixlen 64 autoconf temporary 
  nd6 options=1
  vlan: 1003 parent interface: en0
  media: autoselect (1000baseT )
  status: active

It's a little known fact that Apple's Airport base stations actually run the guest network on VLAN 1003, so if you have multiple Airports (including Time Machines) hooked up to the same wired LAN, the additional base stations can forward packets that arrive over Wi-Fi on the guest network to the base station that acts as the home router.

With both the Ziggo modem and the Apple Time Machine set up as routers with a guest network, that means I have no less than four /64s in use:

Ziggo main network: ...00/64 Ziggo guest network: ...03/64 Time Machine main network: ...f0/64 Time machine guest network: ...f1/64

Pretty sweet!

I also finally ran cat 6 UTP from the living room where the cable modem resides to my home office, so I no longer need to wirelessly extend my network from one end of my apartment to the other, which was neither fast nor reliable, or use the tp-link powerline networking adapters, which are rated for 1200 Mbps but only ran at about 60 Mbps in my setup. They would also hang once a month or so.

Now the only thing I need is some 5 Gbps Ethernet USB dongles.

Permalink - posted 2018-11-11

Mixing IPv4 and IPv6 in BGP

▼ When I first started running IPv6 over BGP, I ran into an interesting problem. The Cisco router I was working on had four full BGP feeds over IPv4. But when did show ip bgp, I noticed the router had five copies of each prefix. One of these paths had a really weird next hop address and was marked as unreachable.

Turned out those were IPv4 prefixes learned over an IPv6 BGP session.

What had happened was that when adding an IPv6 BGP session, I didn't specifically tell the router to not do IPv4 over that session. So despite the session being between two IPv6 addresses, the routers on both sides negotiated the use of the IPv4 unicast address family over that session, and thus exchanged IPv4 prefixes.

The problem with that is that BGP's automatic next hop processing then doesn't work: normally, the next hop is set to the IP address the router uses for the TCP session that BGP runs over. So when router 192.0.2.1 sends IPv4 prefixes to router 192.0.2.2, it sets the next hop attribute in those updates to 192.0.2.1. That doesn't work so well when the IP addresses for that BGP session are 2001:db8::1 and 2001:db8::2. What actually seems to happen is that the routers set the IPv4 next hop address to the first 32 bits of the IPv6 address used for the BGP TCP session...

So this is why for eBGP, we recommend using an IPv4 BGP session to exchange IPv4 prefixes and an IPv6 BGP session to exchange IPv6 prefixes. As the default is IPv4, for IPv6 BGP sessions you usually need to disable IPv4 and enable IPv6 (unless the defaults have been changed at some point, but you really don't want to depend on that):

!
router bgp 65550
 neighbor 2001:db8::2 remote-as 65551
!
 address-family ipv4
 no neighbor 2001:db8::2 activate
!
 address-family ipv6
 neighbor 2001:db8::2 activate
!

Or you can make a route map that sets the next hop address to an address that does work.

For iBGP, it's often easier to also use the IPv4 BGP sessions for IPv6, as the number of iBGP sessions adds up quickly and iBGP doesn't modify the next hop address, so the issue above doesn't come up.

However, there's an additional complication when mixing IPv4 and IPv6 in BGP: debugging gets much harder.

If you want to see what's happening with your BGP sessions, you can use the show bgp ipv4 unicast summary and show bgp ipv6 unicast summary commands:

# show bgp ipv4 unicast summary Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 223.223.223.81 4 81 23 24 0 0 0 00:20:28 16 2001:1c00:161d:df00::1 4 81 24 24 0 0 0 00:20:27 19

# show bgp ipv6 unicast summary Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 2001:1c00:161d:df00::1 4 81 26 26 0 0 0 00:22:01 1

So with these commands, we get to see the BGP sessions for which IPv4 or IPv6 is activated, regardless of whether the session runs over IPv4 or IPv6. So far, so good. And in later Cisco IOS versions, I believe this works the same for other show bgp commands. But under older IOS versions the IPv4 commands won't always take an IPv6 address and vice versa.

But at least under Cisco IOS, the commands now make a reasonable amount of sense: rather than show ip bgp ... for IPv4 and show bgp ... for IPv6, we can now use the much more consistent show bgp ipv4 unicast ... and show bgp ipv6 unicast ... commands.

Not so much under Quagga, though. At least, under version 0.99.22.4. The good news is that you can actually use show ip bgp neighbors <IPv6 address> and show bgp neighbors <IPv4 address>. The bad news is that even though Quagga understands the show bgp ipv4 unicast summary command, it doesn't understand the show bgp ipv4 unicast neighbors ... command. You have to use show ip bgp neighbors ... instead.

So the moral of the story is that you make life a lot easier if you don't mix IPv4 and IPv6 in BGP. If you do, it helps to use recent software, but make sure you check all the possible variations of the different commands, because they're not necessarily used consistently.

Permalink - posted 2016-03-18