1

Multi Topology Routing for OSPFv3

(draft-mirtorabi-mt-ospfv3-00.txt)

Sina Mirtorabi (sina@cisco.com)

222

Agenda

• MTRv3 Goal

• Potential Solutions

• Proposed Solution

• Default topology

• New LSAs

• MT-ID

• MT routing operations

• Backward compatibility

333

MTRv3 Goal

• Define multiple independent topology within a physical topology

Traffic separation across the network, an enterprise where different entities requires traffic separations

Use some links only for some type of traffic such as low delay

444

Potential Solutions

• Using Different Instance IDs

Use Instance IDs in the range of an AF (draft-ietf-ospf-af-alt-00.txt) to have multiple topologies. Scaling issues due to multiple adjacencies, databases etc..

• Using an integrated approach with existing LSAs

Possible to replicate link descriptions in router-LSA for MTR. Issues with backward compatibility

Still doesn’t solve a need to associate prefixes with different topologies

555

Proposed Solution

• Define new LSAs to carry MT information

• New LSAs will be ignored by old routers, so no backward compatibility issues

• New LSAs are being defined in a TLV style, so that they can also facilitate any future extension in OSPFv3

666

Default Topology

• Default Topology is the topology that is built by using the existing LSAs as specified in OSPFv3

• Other non-default topologies are built by using the new LSAs

• Possibility to use new LSA for default topology when all routers are MT capable

• For that a configurable parameter RFC2740Compatibility is used to control the generation of existing or new LSAs for default topology

777

New LSAs

LSA Function code LS Type Description

1 0xB001 E-Router-LSA

2 0xB002 E-Network-LSA

3 0xB003 E-Inter-Area-Prefix-LSA

4 0xB004 E-Intra-Area-Router-LSA

5 0xD005 E-AS-External-LSA

6 0xB006 E-Group-Membership-LSA

7 0xB007 E-NSSA-LSA

8 0x9008 E-Link-LSA

9 0x3009 E-Intra-Area-Prefix-LSA

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6

U S2 S1 T LSA Function Code

888

New LSAs (cont)

• New LSA payloads are TLV based

• TLV may contain sub-TLVs, this is explicitly indicated by setting a S bit

• E-Router LSA has link description TLV, describing link adjacencies. A Sub-TLV under each link description carries MT information

• Prefix LSAs has TLV under each Address Prefix carrying MT information (MT-ID and corresponding cost)

999

E-Router-LSA

LS Age LS type

Link State ID

Advertising Router

LS sequence number

LS checksum Length

0 0 0 0 W V E B Options

TLV type TLV length

Link-type 0

Interface ID

Neighbor Interface ID

Neighbor Router ID

Sub-TLVs

101010

E-Intra-area-prefix-LSA

LS Age LS type

Link State ID

Advertising Router

LS sequence number

LS checksum Length

#Prefix Referenced LS type

Referenced Link State ID

Referenced Advertising Router

Prefix-Block length PrefixLength 0

Address Prefix

TLVs

111111

E-Inter-area-prefix-LSA

LS Age LS type

Link State ID

Advertising Router

LS sequence number

LS checksum Length

Prefix-Block length PrefixLength 0

Address Prefix

TLVs

121212

MT-ID Fields

• 8 bit MT-ID field present in various LSAs

• MT-ID is accompanied with a MT-ID Metric field which carries a metric specific to a MT

• MT-ID value 0 is reserved for carrying information about Default Topology in the new LSAs

131313

MT routing operations

• A Single adjacency is formed even if the link participates in multiple topologies

• OSPFv3 control packets are sent using IPv6 link local address which is MT independent

• Each topology’s SPT is calculated by using only MT-ID links and associated metric for that topology

• Network LSA is shared by all topologies

• During intra-area / Inter-area / external route calculation for a topology, only prefix belonging to a given MT with their associated metric are considered

141414

Backward Compatibility

• An MT capable router will interact (in Default Topology) with non-MT capable routers by using the existing LSAs

• When all routers are MT capable, RFC2740Compatibility can be set to disable and only extended LSAs are used for Default Topology

151515

We would like

draft-mirtorabi-mt-ospfv3-00.txt

to be accepted as a OSPF WG document