1. Global Locator, Local Locator, and Identifier Split (GLI-Split)
Micheal Menth, Matthias Hartmann, Domink Klien
University of Wurzbrug
Chulhyun Park

2. Contents Introduction Big Picture Addresses Communication Feature
Gateway selection, Traffic Engineering
Interworking with IPv6 nodes
Summary

3. Introduction Routing scalability problem
BGP routing tables in DFZ of Internet includes about 300,000 entries and is growing
To resolve the problem, Locator-ID separation schemes are being proposed
Most of those proposals requires modification of routing architecture

4. Introduction Two types of new architecture
Separation of Core/Edge routing
Uses ID as local locator : still has mobility problem
True Loc/ID split protocol
Clean-slate approach : hard to deploy

5. GLI-Split Split functionality of IP addresses
Global locator, Local locator, and identifier
Backward-compatible with IPv6
ID/locators are encoded in regular IPv6 address
So interworking with IPv6 is simple
GLI-Split facilitates many features:
Provider change, Renumbering, Multihoming, Multipath Routing, Traffic Engineering, Mobility support

6. A Big Picture for GLI-Split

7. Terms GLI-domain GLI-nodes / GLI-gateways Identifier / Locators
Edge networks that implement GLI-Split
cf) classic IPv6 domain
GLI-nodes / GLI-gateways
Nodes / border routers of GLI-domain
Identifier / Locators
Identifier (ID), globally unique identifier
Local locator (LL) for local routing
Global locator (GL) for global routing
Mapping service (MS) for resolution

8. Addresses 128-bit IPv6-style address Three types of addresses
Backward-compatible with IPv6
Uses prefix to distinguish GLI-address
Prefix is distributed by IPv6 backbone
Encodes ID and locator of a node
Three types of addresses
Classified by locator information in address
Identifier address
Local address
Global address
그림 넣기 : 128비트 주소의 구조

9. Identifier address Address composed of ID only (no locator)
IDs are assigned in a similar way from today’s Internet
Both hierarchical or HIP-like assignment will do
Used as an endpoint identifier
Source / destination address at transport

10. Local address Address composed of local locator (LL) + ID
Locator used to route a packet inside a GLI-domain
L bits indicate the address is ‘Local’ address
Checksum is used at transport layer after the locator information is changed (into and from global locator)
Locally allocated according to the network topology and routing needs
DHCP may help the allocation as well as resolution : it serves for non-upgraded nodes

11. Global address Address composed of global locator (GL) + ID
Locator used to route a packet beyond GLI-gateway
G bits indicate the address is ‘Global’ address
GAP bit is used for address preservation
Assigned from ISPs, like current IPv6 prefix assignment

12. Resolution Traditional resolution GLI-Split resolution
Resolve domain name into IP address using DNS
GLI-Split resolution
Step 1
Resolve domain name into IP address
Step 2
If the IP address is classic IPv6 address, route the packet
If the IP address is GLI-address, go to step 3
Step 3
Resolve global/local address from the GLI-address

13. Resolution Resolution mechanism : Two ways Resolution 1. DNS
DNS will return global GLI-address
Resolution 2. Mapping System (MS)
Node will ask the locator of GLI address to its local MS
Local MS returns local GLI-address or ‘negative’
If ‘negative’ is received, the node asks global MS
Negative answer means local MS does not know the appropriate locator for the ID, which leads that the node with that ID is located at the other GLI-domain

14. Communication of GLI-upgraded nodes
1. Destination is located in the same GLI-domain
2. Node 4 asks local MS for locator of node 3
0. Node 4 is initiator
3. Local MS returns ‘c’, which is local GLI-address of node 3
1. Node 4 acquires ID of dest.node (3) from a domain name through DNS
4. Node 3 and 4 can communicate each other

15. Communication of GLI-upgraded nodes
2. Destination is located at another GLI-domain
2. Locator is obtained through global MS, because local MS do not know locator of node 3 which is located in another GLI domain
0.Node 1 is source
3. Global locator of source node is updated at GLI-gateway to enable the destination return the packet to source node
1. Again, ID of dest. node (3) is obtained through DNS

16. Communication of GLI-upgraded nodes
2. Destination is located at another GLI-domain
4.Locator of destination node is updated at GLI-gateway to a local locator of the destination node
5.ID and locator of the node 1 is obtained in the same way
6. Again locator of 3 is updated to global address at GLI-gateway
7. Locator of node 3 is updated to local locator for local routing

17. Communication with legacy nodes
Multiple gateway can be a problem : asymmetric path (dealt in the slides left)

18. Gateway selection Enforcing a certain gateway for outgoing packets
At sender side:
Source stores destination GLI-address in the packet’s ‘address buffer’
Address buffer can be added as an ‘optional’ header in the IPv6 header
Source sends the packet to a GLI gateway using gateway’s address as destination
GLI gateway in source GLI-domain strips off and substitutes the destination address with buffered address

19. Gateway selection At receiver side:
If destination GLI-domain is multi-homed, packets in reverse-direction flow may uses different global address from the global address that has been sent from sender
Global destination address of forward direction packet is different from Global source address of reverse direction packet

20. Gateway selection At receiver side:
Sender sets ‘Global Address Preservation’ bits in its header
With GAP bit set
GLI-gateway at destination GLI-domain stores the global address of destination node in the packet’s address buffer
Receiver sets destination address of reverse-direction packet as the global address stored in the buffer

21. Traffic Engineering Self-Initialized communication TE
Use gateway selection mechanism
Incoming communication TE
TE requires support of DNS / MS
Ex) a GLI-domain is connected to cheap ISP E and expensive ISP F
Nodes store mapping entry “E(g).1”, “F(g).10” into DNS / MS
The nodes in the GLI-domain can provide premium service with ID 10, and best-effort service with ID 1

22. IPv6 interworking DNS modification
DNS is configured to return a global GLI-address with GAP bit set to a GLI-node
But, if a node sent query is classic IPv6 node, the node will use this GLI-address as the destination address
So, local DNS should return local GLI-addresses and be contacted within the GLI-domain

23. IPv6 interworking Address Symmetry assurance by GLI-gateway
GLI-gateway stores a map between external src/dest pairs and internal src/dest pairs
Src/dest address of incoming (from classic IPv6 node) packet is substituted using the stored map at the GLI-gateway
Also src/dest address of outgoing (reverse-direction) packet is substituted at the gateway

24. IPv6 interworking
NAT support by GLI-gateway

25. It results in a ‘source routing’ by the gateway N
IPv6 interworking
Local traffic with global GLI-address
If classic IPv6 node in GLI-domain acquires ‘global’ GLI address instead of ‘local’ GLI address in the same GLI domain..
Gateway substitutes the source address and set GAP bit to preserve the source address at the receiver
It results in a ‘source routing’ by the gateway N

26. Benefits of GLI
“Hosts” need not to be configured with any Global Locators
Traffic engineering, renumbering, multi-homing, mobility, …, without ‘provider-independent’ addresses
Result in routing scalability
Routing table size in DFZ held in a certain level

27. Other Benefits For early-adaptor of GLI-Splits
They can get all the advantages of GLI-Split
Moreover, no problem in communication with classic Internet nodes
For Classic IPv6 nodes in GLI-domain
Without GLI-upgrade, legacy nodes still can communicate with GLI-upgraded nodes
This property can lead to incremental deployment
Also GLI-gateway can serve ‘renumbering’ or ‘multi-homing’ to non-upgraded nodes

28. Conclusion
GLI-Split implements LOC/ID split concept within current IPv6 Internet
GLI-Split solves the routing scalability problem with its ‘incremental deployable’ property as well as many problem from LOC/ID coupling

29. Appendix A. RFC 6115 discussion
Critique
At most 3 level lookup
Domain -> ID -> local locator (or negative -> global locator)
Burden to (especially thin or light) hosts
Backward compatibility
‘Why do we need to upgrade our hosts?’
Smaller namespace
64bit IDs, less than 64bit locators

30. Appendix A. RFC 6115 discussion
Rebuttal
At most 3 level lookup
Lookup at host is not a burden, compared to the cost of the same lookup at the gateways

31. Appendix B. Transport Layer
Addressing symmetry
Reverse direction flow will interchange the source and destination address in forward direction flow
Most of transport protocols / application expects the addressing symmetry property is kept
GLI-Split resolved the problem with vertical address translation

32. Appendix B. Transport Layer
At transport layer, ident. addr. is used
At network layer, local/global addr. is used

33. Appendix B. Transport Layer
TCP Checksum compensation
TCP checksum is calculated using source/destination address in IP header
NAT in today’s Internet treats this problem by re-computing TCP checksum when translating addresses
IP translation of GLI-Split may result in a checksum problem
Only in legacy node communication : GLI-nodes communication uses identifier addresses
Uses ‘checksum’ part for backup of TCP checksum calculation

34. Appendix C. Multipath
To use multipath, a GLI-node queries the global MS for the set of multiple addresses that can use
Use ‘Gateway selection’ mechanism of GLI-Split, source node can use multiple stream between source itself and the destination node

35. Appendix D. Mobility Support
Natively supported by GLI-Split itself
Because ID and locator are separated
But only when two communicating nodes are both GLI-upgraded nodes
Otherwise, just use mobile IPv6
Use a GLI address as static home address, and the DNS store it
When a mobile node moves into a GLI domain, it is given new local/global address, and update the local/global MS with the new addresses
Mobile node also informs CNs with new address
By this, GLI-Split mobility support can avoid triangle routing

36. Appendix E. Security ID hijacking
If GLI-node uses cache for ID-to-GL mapping, ID hijacking is possible
Validation for unknown ID-to-GL mapping at gateway can be a defense to the hijacking

37. Appendix E. Security Flow interception
Malicious gateway can send ‘mobility update’ message to communicating gateways
With Sign and verification of mobility update message the problem can be avoided

38. Appendix E. Security Flow interruption
An attacker X can interrupt flow between an other classic IPv6 node C and a multi-homed GLI node G over GLI-gateway B1
By sending a packet through the different gateway B2 from B1, G will send reverse-direction packet through B2
If GLI node does not update the gateway information for an ongoing session, the problem can be avoided