Multi Topology Routing for OSPFv3
(draft-mirtorabi-mt-ospfv3-00.txt)
Sina Mirtorabi
(sina@cisco.com)
1
Agenda
• MTRv3 Goal
• Potential Solutions
• Proposed Solution
• Default topology
• New LSAs
• MT-ID
• MT routing operations
• Backward compatibility
2
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
3
Potential Solutions
• Using Different Instance IDs
 Use
Instance IDs in the range of an AF (draft-ietfospf-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 routerLSA for MTR. Issues with backward compatibility
 Still doesn’t solve a need to associate prefixes
with different topologies
4
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
5
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
6
New LSAs
1
U
2
3
S2 S1
4
5
T
6
7
8
9
0
1
2
3
4
5
6
LSA Function Code
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
7
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)
8
E-Router-LSA
LS Age
LS type
Link State ID
Advertising Router
LS sequence number
LS checksum
0000WVEB
Length
Options
TLV type
TLV length
Link-type
0
Interface ID
Neighbor Interface ID
Neighbor Router ID
Sub-TLVs
9
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
10
E-Inter-area-prefix-LSA
LS Age
LS type
Link State ID
Advertising Router
LS sequence number
LS checksum
Prefix-Block length
Length
PrefixLength
0
Address Prefix
TLVs
11
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
12
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
13
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
14
We would like
draft-mirtorabi-mt-ospfv3-00.txt
to be accepted as a OSPF WG document
15