Type 1 LSAs are the Router LSAs each router in an area originates a Type 1 LSA. The Type 1 LSA describes the state and cost of the routers interfaces inside the area. If the router has more than one interface inside an area all interfaces must be described in a single Type 1 LSA. Type 1 LSAs have area local scope and ONLY flooded within a single area.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 Nt|W|V|E|B| 0 | # links |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | # TOS | metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TOS | 0 | TOS metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Common 20 byte header
- LS Age: The time in seconds since the LSA was originated.
- Options: Optional Capabilities supported.
- LS Type: The Type of the LSA — Type 1 in this case the Router LSA.
- Link State ID: Identifies the piece of the routing domain that
is being described by the LSA
LS Type Link State ID
_______________________________________________
1 The originating router's Router ID.
2 The IP interface address of the
network's Designated Router.
3 The destination network's IP address.
4 The Router ID of the described AS
boundary router.
5 The destination network's IP address.- Advertising Router: The Router ID of the router that originated the LSA.
- LS Sequence Number: Used for old or duplicated LSA detection
- LS Checksum: Checksum of the complete LSA including the header
Type 1 LSA
- bit V: V is for virtual link endpoint.
- bit E: When set, the router is an AS boundary router (E is for
external). - bit B: When set, the router is an area border router (B is for border).
- # links: The number of router links described in this LSA. The total interfaces in the area.
The following fields are used to describe each interface in the area
Type Description
__________________________________________________
1 Point-to-point connection to another router
2 Connection to a transit network
3 Connection to a stub network
4 Virtual link- Link ID: Identifies the object that this router link connects to. Value depends on the link’s Type. When connecting to an object that also originates an LSA (i.e., another router or a transit network) the Link ID is equal to the neighboring LSA’s Link State ID. This provides the key for looking up the neighboring LSA in the link state database during the routing table calculation.
Type Link ID
______________________________________
1 Neighboring router’s Router ID
2 IP address of Designated Router
3 IP network/subnet number
4 Neighboring router’s Router ID- Link Data: Value again depends on the link’s Type field. For connections to stub networks, Link Data specifies the network’s IP address mask. For unnumbered point-to-point connections, it specifies the interface’s MIB-II ifIndex value. For the other link types it specifies the router interface’s IP address. This latter piece of information is needed during the routing table
build process, when calculating the IP address of the next hop. - # TOS ( Type Of Service): The number of different TOS metrics given for this link, not counting the required link metric.
- metric: The cost of using this router link.
- TOS: Type of Service
- TOS metric: TOS-specific metric information.
Router LSA — Type 1: Router LSAs example in Junos
- The operational mode command
show ospf database router
- The command shows all router LSAs in all areas
- Can use
area,advertising-router,lsa-idto narrow down the output results - Can use the
detailandextensiveflags to tailor output level of detail - Can use the
summaryflag for an overview of the LSAs
R2’s Originated — Router-LSA for AREA 0.0.0.0
LS age = 697
Options = (B-bit)
LS type = 1 Router-LSA
ID = 172.30.5.2 RT2's router ID
Adv Rtr = 172.30.5.2 RT2's router ID
bit E = 0 not an AS boundary router
bits 0x1(B = 1) area border router
link count = 3 3 attached interfaces in AREA 0
Link ID = 172.30.0.14 DR interface IP
Link Data = 172.30.0.13 R2’s Interface IP
Type = 2 Connects to Transit Network
# TOS metrics = 0 Type of Service
metric = 1
Link ID = 172.30.0.18 DR interface IP
Link Data = 172.30.0.17 R2’s Interface IP
Type = 2 Connects to Transit Network
# TOS metrics = 0 Type of Service
metric = 1
Link ID = 172.30.5.2 R2’s Loopback
Link Data = 255.255.255.255 Subnet Mask
Type = 3 Connects to STUB network
# TOS metrics = 0
metric = 0
Type = Transit Link Type
Node ID = 172.30.0.18 DR Interface IP
Type = Transit Link Type
Node ID = 172.30.0.14 DR Interface IP
Gen Timer = 00:36:46 How long until LSA regeneration
Aging time = 00:39:47 How long until the LSA expires
Installed = 00:20:13 LSA was installed
expires in = 00:48:23 If not refreshed
sent = 00:11:35 ago LSA was flooded
Last changed = 4d 17:22:47 ago The route was installed
Change Count = 19 Number of times the route was changed
Ours Indicates that this is a local advertisement