OSPF Topology-Transparent Zone Huaimo Chen, Renwei Li (Huawei) Gregory Cauchie (France Telecom) Ning So (Verizon)

Page 2 Contents  Why TTZ?  What is TTZ?  Introduction  How TTZ?

Page 3 Introduction What happens if a network is bigger and bigger? Scalability Issue, Slower convergence, etc. Problems in Current Solution Using Area ›Limitation on Scalability: at most two levels of hierarchies ›Very complex to provide end to end services ›Service interruptions when splitting ASes/Areas since Network Architecture is changed significantly ›Harder to operate & maintain network with more/multiple ASes & areas ›Not easy for applications/software to be aware of/drive/control networks with more/multiple ASes and areas in near future ›Harder for inter-cloud networking with more/multiple ASes and areas TTZ may resolve these issues

Page 4 Contents  Why TTZ?  What is TTZ?  Introduction  How TTZ?  Definition of TTZ  Configuring OSPF TTZ  TTZ vs Area

Page 5 Definition of TTZ A group of routers connected by links with TTZ ID  which is virtualized as a group of TTZ edge routers fully connected or a single router  of which routers outside TTZ are NOT aware  through which LSAs outside are distributed

Page 6 As a Group of Edge Routers Connected (Animated) A group of routers connected by links with attribute TTZ ID. Routers outside of TTZ are NOT aware of TTZ, just see the edge routers of TTZ, which are connected. Links, routers inside TTZ are NOT advertised to routers outside of TTZ. R6 R7 R8 R10 R9 R4 R1 R2 R11 R3 R5 T4 T2 T5 T8 T3 T9 T10 T1 T7 T6 TTZ T4 T3 T10 T1

Page 7 TTZ as a Single Router (Animated) Routers outside of TTZ are NOT aware of TTZ, Just see TTZ as a Single Router. R6 R7 R8 R10 R9 R4 R1 R2 R11 R3 R5 RT T4 T2 T5 T8 T3 T9 T10 T1 T7 T6 TTZ

Configuring OSPF TTZ Configurations on router R2: router ospf 1 Interface ethernet 1/0 ip address /24 Interface ethernet 2/0 ip address /24 ttz Interface ethernet 3/0 ip address /24 ttz Interface ethernet 4/0 ip address /24 ttz No configuration changes on router outside TTZ Configurations on router P1: router ip ospf 1 Interface ethernet 0/0 ip address /24 Interface ethernet 1/0 ip address /24 San Francisco R1 R2 R3 R4 P1 P2 Eth0/0 Eth1/0 Eth2/0 Eth3/0 Eth4/0 Eth3/0 Eth4/0 Eth3/0 Eth1/0 Eth0/0 Eth1/0 Eth2/0 TTZ OSPF Configure TTZ ID on an interface in TTZ

TTZ vs Area OSPF TTZ:  Virtualize TTZ as a router or a group of routers  Can see through a TTZ  2+ levels of hierarchies  Easy to set up TE LSP crossing TTZs  Minor network architecture changes when TTZ is used in a network OSPF Area:  2 levels of hierarchies  Complex to set up TE LSP crossing areas  Significant network architecture changes when multiple areas are introduced to a network TTZ has functions of Area & improves on Area

Page 10 Contents  Why TTZ?  What is TTZ?  Introduction  How TTZ?  Improves Scalability 1 Order of Magnitude  E2E Services Can Be Set Up Easily  Higher Availability

Improves Scalability:1 Order of Magnitude (Animated) R5 R6 R7 R9 R8 R3 R1 R10 R2 R4 RT1 T3T3 T10 T10 T3T3 T10 T10 T3T3 T10 T10 T3T3 T10 T10 T3T3 T10 T10 T3T3 T10 T10 T3T3 T10 T10 T3T3 T10 T10 T3T3 T10 T10 T3T3 T10 T10 T4 T2 T5 T8 T3 T9 T10 T1 T7 T6 TTZ 1 One more hierarchies Area 0 Area 1 TTZ Area 0 Area 2 Area 3 Area 4

E2E TE LSP can be set up easily (Animated) Path for LSP is computed easily in a normal way LSP can be set up along the path computed R5 R6 R7 R9 R8 R3 R1 R10 R2 R4 T4 T2 T5 T8 T3 T9 T10 T1 T7 T6 TTZ Source Destination Find path from R3 to R6 in a normal way Find path from T4 to T10 in a normal way T4 T3 T10 T1

Higher Availability The routing tables on P1 and P2 are not re-calculated. There will be no downloading from RIB to FIB. When considering more complex POPs as TTZs, a failure or crash of a router inside a POP will not affect anything outside of POP. And thus availability is higher. Suppose the Link R2-R3 Is Broken Routers outside not aware of this P1 P2 Eth0/0 Eth1/0 Eth0/0 Eth1/0San Francisco R1 R2 R3 R4 Eth2/0 Eth3/0 Eth4/0 Eth3/0 Eth4/0 Eth3/0 Eth2/0 TTZ

Issues in a Bigger Network: Split to Areas (animated) 1. Significant changes on Network Architecture and configuration when split area, service may be interrupted

TTZ Avoids Splitting to Areas (Animated) 1. No need to split area (one area) 2. Smaller changes on Network Architecture and configuration, network is more stable T3T3 T10 T10 T3T3 T10 T10 T3T3 T10 T10 T3T3 T10 T10 T3T3 T10 T10 T3T3 T10 T10 T4 T2 T5 T8 T3 T9 T10 T1 T7 T6 TTZ 1 Area 0 T4 T3 T10 T1 T3T3 T T T3T3 T

Page 16 Contents  Why TTZ?  What is TTZ?  Introduction  How TTZ?  OSPF Data Change — I bit  LSA Generation and Flooding  Adjacency Establishment  Routing Table Computation

Page 17 OSPF Data Change — I bit 1 bit to identify if a link is in TTZ 0127 I Link Type I = 1 : Link is in TTZ I = 0 : Link is not in TTZ Meaning of “Link Type” of 7 bits is the same as that of “Link Type” of 8 bits Link Type OptionsLS Age Link State ID LS Sequence Number LS Checksum Advertising Router Length Number of Links I bit = 1 if link in TTZ LS Type = 1 Router Link... Flags Header I bit = 1 if link in TTZ Router LSA

LSA Generation and Flooding Every router in TTZ generates a router LSA containing all the router links, each of which has I bit set to 1 if it is configured with TTZ ID. This LSA is flooded inside TTZ. TTZ virtualized as –A group of routers connected: TTZ edge router constructs a second router LSA and sends it to all its neighbors. This LSA comprises two groups of links. 1.The router links connecting the routers outside of the TTZ from this TTZ edge router. These router links are normal router links. There is a router link for every adjacency between this TTZ edge router and a router outside of the TTZ. 2.The "virtual" router links. For each of the other TTZ edge routers, there is a "virtual" router link to it from this TTZ edge router. The cost of the router link from this TTZ router to one of the other TTZ edge routers is the cost of the shortest path from this TTZ edge router to it. –A single router: DR of TTZ constructs a second router LSA and sends it to all its neighbors. This LSA comprises links between a TTZ edge router and a router outside of TTZ. Page 18

HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential Page 19 Router LSA Generated by T1/T5 to inside TTZ R6 R7 R8 R10 R9 R4 R1 R2 R11 R3 R5 T4 T2 T5 T8 T3 T9 T10 T1 T7 T6 TTZ OptionsLS Age Link State ID (T1) LS Sequence Number LS Checksum Advertising Router (T1) Length Number of Links I=0 for Normal Link LS Type = 1 Router Link: T1 to R2 Router Link: T1 to T5 Flags Header Router Link: T1 to T2 Router Link: T1 to T4 I=1 for TTZ link OptionsLS Age Link State ID (T5) LS Sequence Number LS Checksum Advertising Router (T5) Length Number of Links I=1 for TTZ Link LS Type = 1 Router Link: T5 to T1 Router Link: T5 to T9 Flags Header Router Link: T5 to T4 Router Link: T5 to T6 I=1 for TTZ link

Page 20 Router LSA by T1 to outside TTZ as a Group of Nodes Connected R6 R7 R8 R10 R9 R4 R1 R2 R11 R3 R5 T4 T3 T10 T1 OptionsLS Age Link State ID (T1) LS Sequence Number LS Checksum Advertising Router (T1) Length Number of Links Normal Link LS Type = 1 Router Link: T1 to R2 Router Link: T1 to T10 Flags Header Router Link: T1 to T3 Router Link: T1 to T4 Normal Link (“virtual”)

Page 21 Router LSA Generated to outside TTZ as a Single Node R6 R7 R8 R10 R9 R4 R1 R2 R11 R3 R5 OptionsLS Age Link State ID (RT) LS Sequence Number LS Checksum Advertising Router (RT) Length Number of Links Normal Link LS Type = 1 Router Link: RT to R2 Router Link: RT to R11 Flags Header Router Link: RT to R3 Router Link: RT to R10 Normal Link RT...

Adjacency Establishment Between TTZ edge and non TTZ router, TTZ edge –for TTZ as a group of routers connected sends non TTZ router hellos in a normal way, and sends non TTZ router all the LSAs except for the LSAs belong to TTZ during LSDB synchronization. –for TTZ as a single router RT sends non TTZ router hellos in a normal way but with RT ID, and sends non TTZ router all the LSAs except for the LSAs belong to TTZ during LSDB synchronization. After adjacency is established, when TTZ edge router floods a LSA, –it only floods the LSA that does not belong to TTZ to the non TTZ router through the adjacency between the TTZ edge router and the non TTZ router. Page 22

Page 23 Routing Table Computation T3T3 T10 T10 T3T3 T10 T10 T3T3 T10 T10 T3T3 T10 T10 T3T3 T10 T10 T3T3 T10 T10 T4 T2 T5 T8 T3 T9 T10 T1 T7 T6 TTZ 1 Area 0 T3T3 T T T3T3 T Router in TTZ builds SPF tree using topology it sees

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