H3C Technologies H3C WX6000 Series Access Controllers - Manual (Page 251)

25-17
A Type-3 LSA can be used to advertise a default route, having the Link State ID and Network Mask set
to 0.0.0.0.
4) AS external LSA
An AS external LSA originates from an ASBR, describing routing information to a destination outside
the AS.
Figure 25-19 AS external LSA format
Network mask
Forwarding address
LS age
Linke state ID
Advertising Router
Options 5
LS sequence number
LS checksum Length
Metric
External route tag
...
E 0
Forwarding address
TOS metric
External route tag
E TOS
0 7 15 31
Major fields:
z
Link State ID: The IP address of another AS to be advertised. When describing a default route, the
Link State ID is always set to Default Destination (0.0.0.0) and the Network Mask is set to 0.0.0.0
z
Network Mask: The IP address mask for the advertised destination
z
E (External Metric): The type of the external metric value, which is set to 1 for type 2 external routes,
and set to 0 for type 1 external routes. Refer to
Route types for description about external route
types
z
metric: The metric to the destination
z
Forwarding Address: Data traffic for the advertised destination will be forwarded to this address
z
External Route Tag: A tag attached to each external route. This is not used by the OSPF protocol
itself. It may be used to manage external routes.
5) NSSA external LSA