31 Mar

Dark spot in Global IPv6 routing



Fest time at college – Good since I get lot of free time to spend around looking at routing tables. It’s always interesting since last week was full of some major submarine cable cuts and has huge impact on Indian networks.

Anyways, an interesting issue to post today about Global IPv6 routing . There are “dark spots” in global IPv6 routing because of peering dispute between multiple tier 1 ISPs involving Hurricane Electric (AS6939) & Cogent Communications (AS174).  What’s happening here is that both tier 1 providers failed to reach on agreement to keep peering up in case of IPv6. This has resulted in parts of global IPv6 internet where packets from one network (and it’s downstream) can’t reach other network or their downsteam singled hommed networks. 

Only publicly known information about de-peering of Cogent from HE is Mr Mike Leber’s email to NANOG mailing list here. Overall Hurricane Electric seems pretty much open in peering and networking community knows this well. So it is not hard to believe in to Mr Mike’s mail. Infact they even baked a cake to cheer Cogent up at NANOG meeting 47 at Dearborn, Michigan in 2009.



Why IPv6 Internet is broken when simply two providers de-peered? 

Answer of this lies in fundamental theory of a Tier 1 network i.e a “transit free” network. Hurricane Electric is world’s biggest IPv6 backbone in terms of number of interconnections while Cogent Communications is a big ISP in US and Europe with significant last mile fiber in many areas of US. It is a popular choice for cheap datacenter upstream transit. 

Now since both ISPs are tier 1 i.e transit free network in case of IPv6 internet, they simply do not pay to anyone (on layer 3) to reach any network. Packets from HE can’t go to Cogent simply because there’s no transit provider for HE in IPv6 (infact it is the transit provider to lot of networks!). At the same time Cogent is also not having any transit provider in IPv6. Transit here is important because there are many networks in world which are not connected. Say e.g Indian BSNL doesn’t connects to Hurricane Electric or say Tulip Telecom doesn’t connects to AT&T directly but packets can be routed because in both cases they have transit from an upstream network which eventually connects to AT&T or peers with AT&T. 



Looking at Cogent’s IPv6 prefix – 2001:0550::/32 announced from AS174 from Hurricane Electric’s route server:


route-server> show bgp ipv6 2001:0550::/32
% Network not in table


There is no public route server from Cogent, thus I am using their looking glass to reach IPv6 address of he.net to test connectivity:

PING he.net(he.net) 56 data bytes
From 2001:550:1:31f::1 icmp_seq=2 Destination unreachable: No route
From 2001:550:1:31f::1 icmp_seq=3 Destination unreachable: No route

— he.net ping statistics —
5 packets transmitted, 0 received, +2 errors, 100% packet loss, time 14003ms



Is dark spot just in case of IPv6? What about their IPv4?

Yes, this problem in IPv6 specific only. HE and Cogent do not peer in case of IPv4 too but since HE is not a tier 1 in case of IPv4, it rather has a couple of transit providers who seem to be having peering relation with Cogent.

Looking at Cogent’s IPv4  from HE’s route server:

route-server> show ip bgp long
BGP table version is 0, local router ID is
Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
r RIB-failure, S Stale, R Removed
Origin codes: i – IGP, e – EGP, ? – incomplete

Network Next Hop Metric LocPrf Weight Path
* i38.0.0.0 48 70 0 1299 174 i
* i 60 70 0 1299 174 i
* i 48 70 0 1299 174 i
* i 48 70 0 1299 174 i
* i 48 70 0 1299 174 i
* i 48 70 0 1299 174 i
* i 48 70 0 1299 174 i
* i 48 70 0 1299 174 i
* i 48 70 0 1299 174 i
* i 48 70 0 1299 174 i
* i 48 70 0 1299 174 i
* i 48 70 0 1299 174 i

(short extracted view of long output)


So clearly HE seems using AS1299 which Telia Global Network – one of IPv4 Tier 1 ISPs to reach Cogent. I can guess it is transit provider for HE. At the same time I can see a route from Cogent to HE in IPv4 via Global Crossing:

traceroute to (, 30 hops max, 60 byte packets
1 vl99.mag01.ord01.atlas.cogentco.com ( 0.497 ms 0.444 ms
2 te0-5-0-3.ccr21.ord01.atlas.cogentco.com ( 0.437 ms 0.569 ms
3 te0-5-0-5.ccr22.ord03.atlas.cogentco.com ( 0.647 ms te0-5-0-1.ccr22.ord03.atlas.cogentco.com ( 0.821 ms
4 Tenge4-4-10000M.ar3.CHI2.gblx.net ( 0.554 ms 0.562 ms
5 Hurrican-Electric-LLC.Port-channel100.ar3.SJC2.gblx.net ( 54.313 ms 54.016 ms
6 10gigabitethernet1-1.core1.fmt1.he.net ( 54.792 ms 55.231 ms
7 * *
8 * *


So clearly networks have connectivity in IPv4 via HE’s upstreams Global Crossing (which is now Level 3) & Telia. In IPv6 HE simply is not having a customer relationship with Gblx and Telia. And so the dark spot remains there. 


The other fact which confirms that Telia and Gblx are transit for HE is via RADB records of AS1299.


Anurags-MacBook-Pro:~ anurag$ whois -h whois.radb.net as1299 | grep 6939
import: from AS6939 action pref=50; accept AS-HURRICANE
export: to AS6939 announce ANY
mp-import: afi ipv6 from AS6939 accept AS-HURRICANE
mp-export: afi ipv6 to AS6939 announce AS-TELIANET-V6
Anurags-MacBook-Pro:~ anurag$


Clearly it is announcing ANY ie to HE on IPv4 while for IPv6 it is announcing only AS-TELIANET-V6 i.e transit in IPv4 while peering in IPv6.


With hope that this issue is resolved in near future, time for me to get some sleep! 🙂


Disclaimer: Focus of this blog post is not about who is responsible for not peering & creating such situation but rather a technical analysis of what happens when big Tier 1 ISPs de-peer.

Comments are personal and have nothing to do with my employer. I know most of people I mentioned in this post personally and this fact has nothing to do with this blog post!


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