.. index:: Link State Database
Each router describes their link-state information in a message known as an
-:abbr:`LSA (Link State Advertisement)`, which is then propogated through to all
+:abbr:`LSA (Link State Advertisement)`, which is then propagated through to all
other routers in a link-state routing domain, by a process called `flooding`.
Each router thus builds up an :abbr:`LSDB (Link State Database)` of all the
link-state messages. From this collection of LSAs in the LSDB, each router can
---------------
:abbr:`OSPF` defines a range of mechanisms, concerned with detecting,
-describing and propogating state through a network. These mechanisms
+describing and propagating state through a network. These mechanisms
will nearly all be covered in greater detail further on. They may be
broadly classed as:
OSPF defines several related mechanisms, used to manage synchronisation of
:abbr:`LSDB` s between neighbours as neighbours form adjacencies and the
-propogation, or `flooding` of new or updated :abbr:`LSA` s.
+propagation, or `flooding` of new or updated :abbr:`LSA` s.
.. index:: OSPF Areas overview
The combination of the Type, ID and Advertising Router ID must uniquely
identify the :abbr:`LSA`. There can however be multiple instances of
an LSA with the same Type, LSA ID and Advertising Router ID, see
- :ref:`Sequence Number <ospf-lsa-sequence-number>`.
+ :ref:`sequence number <ospf-lsa-sequence-number>`.
- Age
| Router LSA | Router ID | The :abbr:`OSPF` enabled links of the |
| | | router, within a specific link-state area. |
+-------------+----------------------------+--------------------------------------------+
-| Network LSA | The IP address of the | The subet mask of the network and the |
+| Network LSA | The IP address of the | The subnet mask of the network and the |
| | :abbr:`DR` for the network | Router IDs of all routers on the network |
+-------------+----------------------------+--------------------------------------------+
::
- # show ip ospf database router 192.168.0.49
-
- OSPF Router with ID (192.168.0.53)
-
- Router Link States (Area 0.0.0.0)
-
- LS age: 38
- Options: 0x2 : *|-|-|-|-|-|E|*
- LS Flags: 0x6
- Flags: 0x2 : ASBR
- LS Type: router-LSA
- Link State ID: 192.168.0.49
- Advertising Router: 192.168.0.49
- LS Seq Number: 80000f90
- Checksum: 0x518b
- Length: 60
- Number of Links: 3
-
- Link connected to: a Transit Network
- (Link ID) Designated Router address: 192.168.1.3
- (Link Data) Router Interface address: 192.168.1.3
- Number of TOS metrics: 0
- TOS 0 Metric: 10
-
- Link connected to: a Transit Network
- (Link ID) Designated Router address: 192.168.0.49
- (Link Data) Router Interface address: 192.168.0.49
- Number of TOS metrics: 0
- TOS 0 Metric: 10
-
- Link connected to: Stub Network
- (Link ID) Net: 192.168.3.190
- (Link Data) Network Mask: 255.255.255.255
- Number of TOS metrics: 0
- TOS 0 Metric: 39063
- # show ip ospf database network 192.168.0.49
-
- OSPF Router with ID (192.168.0.53)
-
- Net Link States (Area 0.0.0.0)
-
- LS age: 285
- Options: 0x2 : *|-|-|-|-|-|E|*
- LS Flags: 0x6
- LS Type: network-LSA
- Link State ID: 192.168.0.49 (address of Designated Router)
- Advertising Router: 192.168.0.49
- LS Seq Number: 80000074
- Checksum: 0x0103
- Length: 40
- Network Mask: /29
- Attached Router: 192.168.0.49
- Attached Router: 192.168.0.52
- Attached Router: 192.168.0.53
- Attached Router: 192.168.0.54
+ # show ip ospf database router 192.168.0.49
+
+ OSPF Router with ID (192.168.0.53)
+
+ Router Link States (Area 0.0.0.0)
+
+ LS age: 38
+ Options: 0x2 : *|-|-|-|-|-|E|*
+ LS Flags: 0x6
+ Flags: 0x2 : ASBR
+ LS Type: router-LSA
+ Link State ID: 192.168.0.49
+ Advertising Router: 192.168.0.49
+ LS Seq Number: 80000f90
+ Checksum: 0x518b
+ Length: 60
+ Number of Links: 3
+
+ Link connected to: a Transit Network
+ (Link ID) Designated Router address: 192.168.1.3
+ (Link Data) Router Interface address: 192.168.1.3
+ Number of TOS metrics: 0
+ TOS 0 Metric: 10
+
+ Link connected to: a Transit Network
+ (Link ID) Designated Router address: 192.168.0.49
+ (Link Data) Router Interface address: 192.168.0.49
+ Number of TOS metrics: 0
+ TOS 0 Metric: 10
+
+ Link connected to: Stub Network
+ (Link ID) Net: 192.168.3.190
+ (Link Data) Network Mask: 255.255.255.255
+ Number of TOS metrics: 0
+ TOS 0 Metric: 39063
+ # show ip ospf database network 192.168.0.49
+
+ OSPF Router with ID (192.168.0.53)
+
+ Net Link States (Area 0.0.0.0)
+
+ LS age: 285
+ Options: 0x2 : *|-|-|-|-|-|E|*
+ LS Flags: 0x6
+ LS Type: network-LSA
+ Link State ID: 192.168.0.49 (address of Designated Router)
+ Advertising Router: 192.168.0.49
+ LS Seq Number: 80000074
+ Checksum: 0x0103
+ Length: 40
+ Network Mask: /29
+ Attached Router: 192.168.0.49
+ Attached Router: 192.168.0.52
+ Attached Router: 192.168.0.53
+ Attached Router: 192.168.0.54
Note that from one LSA, you can find the other. E.g. Given the
::
- ------------------------ Network: ......
- | Designated Router IP: 192.168.1.3
- |
- IP: 192.168.1.3
- (transit link)
- (cost: 10)
- Router ID: 192.168.0.49(stub)---------- IP: 192.168.3.190/32
- (cost: 10) (cost: 39063)
- (transit link)
- IP: 192.168.0.49
- |
- |
- ------------------------------ Network: 192.168.0.48/29
- | | | Designated Router IP: 192.168.0.49
- | | |
- | | Router ID: 192.168.0.54
- | |
- | Router ID: 192.168.0.53
- |
- Router ID: 192.168.0.52
+ ------------------------ Network: ......
+ | Designated Router IP: 192.168.1.3
+ |
+ IP: 192.168.1.3
+ (transit link)
+ (cost: 10)
+ Router ID: 192.168.0.49(stub)---------- IP: 192.168.3.190/32
+ (cost: 10) (cost: 39063)
+ (transit link)
+ IP: 192.168.0.49
+ |
+ |
+ ------------------------------ Network: 192.168.0.48/29
+ | | | Designated Router IP: 192.168.0.49
+ | | |
+ | | Router ID: 192.168.0.54
+ | |
+ | Router ID: 192.168.0.53
+ |
+ Router ID: 192.168.0.52
Note the Router IDs, though they look like IP addresses and often are
The address of the router to forward packets to for the route. This may be,
and usually is, left as 0 to specify that the ASBR originating the External
:abbr:`LSA` should be used. There must be an internal OSPF route to the
- forwarding address, for the forwarding address to be useable.
+ forwarding address, for the forwarding address to be usable.
Tag
An arbitrary 4-bytes of data, not interpreted by OSPF, which may carry
::
- # show ip ospf database external 192.168.165.0
- LS age: 995
- Options: 0x2 : *|-|-|-|-|-|E|*
- LS Flags: 0x9
- LS Type: AS-external-LSA
- Link State ID: 192.168.165.0 (External Network Number)
- Advertising Router: 192.168.0.49
- LS Seq Number: 800001d8
- Checksum: 0xea27
- Length: 36
- Network Mask: /24
- Metric Type: 2 (Larger than any link state path)
- TOS: 0
- Metric: 20
- Forward Address: 0.0.0.0
- External Route Tag: 0
+ # show ip ospf database external 192.168.165.0
+ LS age: 995
+ Options: 0x2 : *|-|-|-|-|-|E|*
+ LS Flags: 0x9
+ LS Type: AS-external-LSA
+ Link State ID: 192.168.165.0 (External Network Number)
+ Advertising Router: 192.168.0.49
+ LS Seq Number: 800001d8
+ Checksum: 0xea27
+ Length: 36
+ Network Mask: /24
+ Metric Type: 2 (Larger than any link state path)
+ TOS: 0
+ Metric: 20
+ Forward Address: 0.0.0.0
+ External Route Tag: 0
We can add this to our partial topology from above, which now looks
projects / mirror_frr.git / blobdiff