IPv6 Migration

Implementation of IPv6 on GÉANT began with the migration of the network’s Internal Gateway Protocol (IGP) from its original OSPFv2 to IS-IS. This was necessary because, although the routers could already provide dual-stack forwarding, dynamic routing protocols had to be implemented across the backbone in order for the actual network to operate in dual-stack fashion. This also ensures GÉANT will remain at the forefront of future networking developments.

IS-IS Migration

At the time of the IGP migration in September 2002, we had the option of choosing OSPFv3. OSPv3 was a new protocol and needed extensive lab testing to address interoperability and stability issues before it could be introduced in a production environment. Due to time scheduling and for optimisation reasons, we decided to migrate to IS-IS and remove OSPFv2 from the core backbone.

IS-IS is an OSI protocol which has been used by many operators for a long time now. The advantage of IS-IS is having one single database for any type of IP protocol. In addition it is a very flexible protocol, and usually, the latest developments and enhancements are implemented by vendors on IS-IS first.

The migration process took 6 weeks in total, from planning and preparation through to completion. DANTE’s engineers drew on the previous experience of engineers from Abilene in migrating IGP. An IS-IS training programme was also provided by Juniper to ensure necessary levels of knowledge were achieved in advance of the migration.

DANTE tested and validated the migration in a laboratory environment for 1 week, before performing the migration for real on GÉANT’s 22 core routers across Europe.

We employed the following migration plan:

Make OSPFv2 the preferred IGP in all cases: increase the distance/preference of the IS-IS protocol from standard value to 169 for level 1 and level 2 routes (even if we configured all the interfaces in level 2 only).
Configure IS-IS in the core.
Count the number of routes in the OSPF database and IS-IS database (they should be the same).
Disable OSPF PoP by PoP on Juniper routers and cancel it on Cisco routers.
For each PoP migrated, count the routes transferred from OSPF to IS-IS and verify that no route has disappeared.
After 24 hours of monitoring, cancel OSPF configuration on all the routers.

The actual migration took place overnight, over a period of 3 hours. In practice, OSPFv2 and IS-IS were cohabiting on GÉANT during this time, before OSPF was deactivated on each router in turn to complete the move to IS-IS.

No interruption of services was experienced during the migration.

Once the IGP migration was complete, work began on implementing native IPv6 on the GÉANT backbone in dual core fashion. For each router to perform native forwarding of IPv4 and IPv6 packets, IPv4 and IPv6 addresses had to be configured on the core backbone.

BGP and IS-IS Interoperability Tests

Use of BGP with IPv6 was also tested in the laboratory environment, and the GÉANT core backbone was then reconfigured internally with a full mesh I-BGP for each of v4 and v6, in place of its then single I-BGP mesh. With the separate meshes in place, IS-IS continues to be used to route IPv4 traffic as well as that for IPv6. IPv6 addresses were assigned not only to the core GÉANT routers but also to trunks and access links.

IS-IS Topology

IS-IS setup for GÉANT is relatively simple, with all the routers configured at Level 2 only. This choice is due to the fact that GÉANT is built with 23 routers. Each PoP (except that in Germany) has one router which operates as edge and core router. If GÉANT were to increase in size with more routers per PoP, a hierarchy with two levels could be designed, with a level 1 area per POP and a level 2 area for the core backbone.

A further reason for keeping all routers at level 2 is the fact that we have configured MPLS-TE; we wanted to avoid troubleshooting a two-level IS-IS hierarchy with MPLS-TE deployed.

More details about IS-IS setup are available in the documents linked alongside.