1. Tag Switching RFC Cisco systems Tag Switching architecture overview. Switching In IP Networks - B.Davie, P.Doolan, Y.Rekhter. Presnted By - Shmuel Vagner.

2. Overview b A label swapping protocol that allows: Destination based routing.Destination based routing. Hierarchies of routing knowledge.Hierarchies of routing knowledge. Multicast routing.Multicast routing. Explicit routes.Explicit routes.

3. Overview b Advantages: Better performance.Better performance. Hardware and data-link independent but at the same time can benefit from fast data-link protocols like ATM.Hardware and data-link independent but at the same time can benefit from fast data-link protocols like ATM. Scalable.Scalable. Flexible.Flexible.

b TSR - Tag Switching router. b TSER - Tag Switching edge router. 4. Overview

5. Components b Forwarding Component Responsible for forwarding incoming packets:Responsible for forwarding incoming packets: –The routing entry is found using a tag, carried by the incoming packet. –A new data-link address and a new tag are swapped into the outgoing packet. –The altered packet is sent over the outgoing interface specified in the routing entry.

6. Components b Control Component Responsible for creation of tags.Responsible for creation of tags. Responsible for binding between tags and routing entries.Responsible for binding between tags and routing entries. Responsible for distribution of tags to other TSRs.Responsible for distribution of tags to other TSRs.

7. Destination Based Routing b A typical routing table consist of routing entries that correspond to forwarding equivalence classes (FEC). b The routing table is populated using standard routing protocols like: RIP, OSPF, BGP etc… b Tag switching uses the information obtained by these protocols to construct it’s tag forwarding information base (TFIB)

8. Destination Based Routing (Tag Distribution) b Three techniques for tag distribution: Downstream distribution.Downstream distribution. Downstream on demand distribution.Downstream on demand distribution. Upstream distribution.Upstream distribution.

9. Destination Based Routing (Tag Distribution) b Downstream distribution: An FEC entry is obtained by a routing protocol.An FEC entry is obtained by a routing protocol. A Tag is allocated for the entry from a pool of free tags.A Tag is allocated for the entry from a pool of free tags. The FEC entry is placed in the TFIB under the allocated tag.The FEC entry is placed in the TFIB under the allocated tag. A tupple is sent to each adjacent TSR.A tupple is sent to each adjacent TSR. Upon receiving a tupple from the next hop TSR, the TSR updates the TFIB entry.Upon receiving a tupple from the next hop TSR, the TSR updates the TFIB entry.

10. Destination Based Routing (Tag Distribution) b On demand downstream distribution: Same as downstream, with the exception that TSR explicitly request for outgoing tag information.Same as downstream, with the exception that TSR explicitly request for outgoing tag information. b Upstream distribution: The TSR allocates outgoing tags and receives incoming tag information from other TSRs.The TSR allocates outgoing tags and receives incoming tag information from other TSRs.

11. Destination Based Routing (Tag Distribution) b Weak points: Upstream requires a TFIB per interface.Upstream requires a TFIB per interface. Upstream will work only with point to point links.Upstream will work only with point to point links. Upstream requires the TSRs to know the tag ranges of each other.Upstream requires the TSRs to know the tag ranges of each other. Downstream send more messages then necessary.Downstream send more messages then necessary. Downstream on demand makes the protocol more complex and cannot be piggy-backed.Downstream on demand makes the protocol more complex and cannot be piggy-backed.

12. Destination Based Routing (Tag Distribution) b Tags can be distributed by standard routing messages. Will work well with BGP (as a BGP attribute).Will work well with BGP (as a BGP attribute). Not suitable for OSPF (Only adjacent nodes should be updated).Not suitable for OSPF (Only adjacent nodes should be updated). Not suitable for RIP (The protocol software should be upgraded).Not suitable for RIP (The protocol software should be upgraded). b Tags can be distributed using a dedicated Tag Distribution Protocol (TDP).

13. Example

14. Routing Changes Example

15. Routing Hierarchies b Interior Routers in transit domains currently have to store enormous routing tables that contain FEC entries to each possible destination. b Storing FEC entries to edge routers should be enough! b Advantages: Fault Isolation.Fault Isolation. Better Performance Better Performance

16. Routing Hierarchies b The TFIB of internal TSRs contains only FEC entries that associated with destinations within the domain. b TSERs maintain full routing tables and thus know to what TSERs to route packets that enter the domain. b TSERs can also use tag switching between themselves by stacking tags.

17. Example Intra-domain entriesInter-domain entries V:5 T:2,10X:2,12Y:2,17W:6

18. Multicast b Key features: Allows a source to send a single message to multiple sources.Allows a source to send a single message to multiple sources. Structured as a tree.Structured as a tree. Hello messages are sent to advertise a multicast tree.Hello messages are sent to advertise a multicast tree. Join messages are sent to join a multicast tree.Join messages are sent to join a multicast tree. Allows efficient use of link - layer protocols with multicast capabilities (Ethernet).Allows efficient use of link - layer protocols with multicast capabilities (Ethernet).

19. Multicast b Tag Switching related issues: No two TSRs on a common sub-network may bind the same tag to different multicast trees.No two TSRs on a common sub-network may bind the same tag to different multicast trees. All TSRs in a sub-network belonging to a common multicast tree, should agree on the same tag for the tree.All TSRs in a sub-network belonging to a common multicast tree, should agree on the same tag for the tree.

20. Multicast b Solution: The solution is PIM specific.The solution is PIM specific. TFIBs are stored on a per interface basis.TFIBs are stored on a per interface basis. TSRs advertise the range of tags they use for local bindings via PIM Hello messages.TSRs advertise the range of tags they use for local bindings via PIM Hello messages. When TSR wants to join a tree it advertise it’s tag for the tree via PIM Join message.When TSR wants to join a tree it advertise it’s tag for the tree via PIM Join message. TSRs listen to all join messages over a common sub-network, and thus learn which tags belong to which trees.TSRs listen to all join messages over a common sub-network, and thus learn which tags belong to which trees.

21. Example AB C E D

22. RSVP b Tags are associated to locally to flows. b The TFIB entry contains resource reservation information. b A new RSVP object, a tag object is defined. b Tags are distributed via RSVP Resv messages in Tag objects.

23. Explicit Routing b Allows a source router to predefine the route that a class of incoming packets will take. b The route is described as a sequence of entries. b The advertised route is carried in RSVP Path messages. b The tag binding is achieved via RSVP Resv messages as before.

24. Tag Switching over ATM b Tag switching can be performed using ATM hardware. b The ATM Control plane is replaced with a Tag switching component. b Tag information is carried in the VCI field (And the VPI field if routing hierarchies are supported) of the ATM header. b The same TSR can act both as tag switch and ATM switch by dividing tag ranges.

25. Tag Switching over ATM b Cell Interleaving Problem: Packets with same tags are broken into cells.Packets with same tags are broken into cells. Cells may interleave at the next hop router.Cells may interleave at the next hop router. Packets cannot be reconstructed at destination.Packets cannot be reconstructed at destination.

26. Tag Switching Over ATM b Call Interleave solutions: VC MergeVC Merge –Cells are not forwarded until end of packet detected. –Disadvantage - May require Hardware Modifications. Multiple Tags per Route:Multiple Tags per Route: –Use Upstream tag distribution. –Disadvantage - Consumes many tags, bad scalability.

27. Tag Distribution Protocol b Uses Incremental approach. b Protocol Messages: TDP_PIE_OPEN - TSR say hello to neighbor.TDP_PIE_OPEN - TSR say hello to neighbor. TDP_PIE_BIND - A binding distribution message.TDP_PIE_BIND - A binding distribution message. TDP_PIE_WITHDROW_BIND - Deprecation of previously advertised binding.TDP_PIE_WITHDROW_BIND - Deprecation of previously advertised binding. TDP_PIE_REQUEST_BIND - An explicit request for binding information.TDP_PIE_REQUEST_BIND - An explicit request for binding information.

28. Tag Distribution Protocol b Protocol Messages (Cont.): TDP_PIE_RELEASE_REQUEST - Release of previously requested binding. TSR may choose to delete a binding after receiving this message.TDP_PIE_RELEASE_REQUEST - Release of previously requested binding. TSR may choose to delete a binding after receiving this message. TDP_PIE_NOTIFICATION - Conveys errors.TDP_PIE_NOTIFICATION - Conveys errors. TDP_PIE_KEEP_ALIVE - Obvious.TDP_PIE_KEEP_ALIVE - Obvious.

29. Summary b Based on label swapping. b Supports a big variety of routing functions. b Can be implemented by ATM and Non-ATM hardware. b Enables Routing Hierarchies.