3Com MSR 50 Series Configuration Manual page 934

934 C 58: OSPF C
HAPTER
n
ONFIGURATION
A type3 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 287 AS external LSA format
0
LS checksum
E 0
E TOS
Major fields:
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
Network Mask: The IP address mask for the advertised destination
■
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
types" on page 924
metric: The metric to the destination
■
Forwarding Address: Data traffic for the advertised destination will be
■
forwarded to this address
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
An NSSA external LSA originates from the ASBR in a NSSA and is flooded in the
NSSA area only. It has the same format as the AS external LSA.
7 15
LS age
Linke state ID
Advertising Router
LS sequence number
Network mask
Forwarding address
External route tag
Forwarding address
External route tag
...
for description about external route types
Options
Length
Metric
TOS metric
31
5
"Route