Filter
Top Products
Figure 6- 107.Routers Links Advertisements
In router links advertisements,the Link State ID field is set to the router’s OSPF Router ID.The T-bit is set in the advertisement’s Option field if and only if the
router is able to calculate a separate set of routes for each IP Type of Service (TOS).Router links advertisements are flooded throughout a single area only.
Field Description
V – bit
When set,the router is an endpoint of an active virtual link that is using the described area as a Transit area (V
is for Virtual link endpoint).
E – bit When set,the router is an Autonomous System (AS) boundary router (E is for External).
B – bit When set,
the r
outer is an ar
ea bor
der router (B is for Border).
Number of
Link
s
The n
umber of r
outer links described b
y this advertisement.This must be the total collection of router links to
the area.
The following fields are used to describe each router link.Each router link is typed.The Type field indicates the kind of link being described. It may be a link to a
transit network,to another router or to a stub network.The values of all the other fields describing a router link depend on the link’s Type.For example, each
link has an associated 32-bit data field.
For links to stub networks this field specifies the network’s IP address mask.For other link types the Link Data specifies
the r
outer’
s associated IP interface address.
Field
Descr
iption
Type A quick classification of the router link.One of the following:Type Description Point-to-point connection to
another r
outer
.
Connection to a transit netw
ork.
Connection to a stub netw
ork.Virtual link.
Link ID Identifies the object that this r
outer link connects to
.
V
alue depends on the link’
s Type.When connecting to an
object that also originates a link state adv
er
tisement (i.e. another router or a transit network) the Link ID is
equal to the neighboring advertisement’s Link State ID.This provides the key for looking up an advertisement in
the link state database.Type Link ID Neighboring router’s Router ID.IP address of Designated Router.IP
network/subnet number. Neighboring router’s Router ID.
Link Data Contents again depend on the link’s Type field.For connections to stub networks,it specifies the network’s IP
ad
dr
ess mask.
F
or unn
umbered point-to-point connection,it specifies the interface’s MIB-II ifIndex value.For
other link types it specifies the router’s associated IP interface address.This latter piece of information is
needed during the routing table build process,when calculating the IP address of the next hop.
No. of TOS The number of different Type of Service (TOS) metrics given for this link,not counting the required metric for
T
OS 0.
If no ad
ditional
T
OS metrics ar
e given,this field should be set to 0.
TOS 0 Metric The cost of using this r
outer link f
or
T
OS 0.
114
Allied Telesyn AT-9724TS High-Density Layer 3 Stackable Gigabit Ethernet Switch
Octets
Router Links Advertisements
Link-State ID
Advertising Router
Link-State Checksum Length
Link-State Sequence Number
01 23
4
Link-State Age Options Link-State Type
Reserved V E B Reserved Number of Links
Link-ID
Link Data
Ty p
eNo. of TOS TOS 0 Metric
TOS 0 Metric
...
TOS 0 Metric
...
Link-ID
Link Data