3Com Router User Manual

Configuring OSPF427
hello packet before this interface sets up neighboring relations with the adjacent 
routers. 
The interface can be configured into nbma mode on the broadcast network 
without multi-access capability.
If not all routers are inter-reachable on NBMA network, the interface can be 
configured into 
p2mp mode.
If the router has only one opposite terminal in NBMA network, the interface can 
also be changed to 
p2p mode.
The difference between an NBMA network and a point-to-multipoint network...

428CHAPTER 29: CONFIGURING OSPF
The default value of the cost of sending a packet on the interface is calculated 
automatically according to the interface baud rate as follows:
The default value is automatically calculated according to interface baud rate.
■If the baud rate is less than 2000 bps, 2000 is taken, and the overhead value is 
100000000/2000=50000. 
■If the baud rate is greater than 100000000 bps, 100000000 is taken, and the 
overhead value is 100000000/100000000=1. 
■If the baud rate is...

Configuring OSPF429
Specifying the Router 
PriorityIt is necessary to establish the peer relationship manually between interfaces for 
multi-point access network, (NBMA and broadcast type networks). But 
establishing peer relationshipoccupies large amounts of system resources when 
there are hundreds of routers in the network. To resolve this issue, OSPF specifies a 
“designated router” (DR). All routers within the same network segment send the 
relationship information to the DR, which broadcasts the...

430CHAPTER 29: CONFIGURING OSPF
Specifying the Hello 
IntervalThe Hello packet is periodically sent to the neighboring router to find and maintain 
OSPF neighbor relationship, and to elect the DR and BDR in the NBMA and 
broadcast networks. When one router is started, it only sends hello packets to the 
neighbors whose precedences are larger than 0, that is, the routers can possibly be 
elected as DR or BDR. You can configure the interval for sending hello packets. If 
the interval is too short, the...

Configuring OSPF431
Specifying the 
Retransmitting IntervalThe router waits for confirmation from the neighbor to whom it has sent an LSA. If 
the router does not receive the neighbors confirmation after a specified interval, 
the retransmitting interval, it resends the LSA. You can set the time interval for 
re-transmitting an LSA.
Perform the following configurations in interface view.
Ta b l e 496   Specify Retransmitting Interval
By default, the retransmitting interval is 5 seconds.
The...

432CHAPTER 29: CONFIGURING OSPF
information is reduced greatly. A default routing (0.0.0.0) is generated for the area 
by the ABR of the area to insure that these routes are reachable. A stub area is an 
optional configured attribute, but it does not mean that each area is configurable. 
Usually, a stub area is located at the boundary of the AS. A non-backbone area 
with only one ABR or multi-ABR that are not virtually connected between ABRs 
can be configured as a stub area.
A “totally stubby area” is...

Configuring OSPF433
In the following group network, an AS operating the OSPF protocol includes three 
areas, area 1, area 2, and area 0. Area 0 is the backbone area. The other ASs 
operate RIP. Area 1 is defined as an NSSA area. After an RIP route advertises to the 
NSSA ASBR that generates a Type-7 LSA and propagates in Area 1. After the 
Type-7 LSA reaches the NSSA ABR, it is transformed into a Type-5 LSA that is 
advertised to Area 0 and Area 2. The RIP route is generated as a Type-5 LSA and...

434CHAPTER 29: CONFIGURING OSPF
which reduces the LSDB in other areas. The configuration of range is only effective 
when it is configured on teh ABR in the stub area.
For example, there are two network segments in an area as follows:
202.38.160.0    255.255.255.0
202.38.180.0    255.255.255.0
They are summarized into one network segment: 202.38.0.0  255.255.0.0
When the summary network segment of a specific network is added to an area, 
the internal routes with the IP addresses that fall in this summary...

Configuring OSPF435
The virtual link is activated after the route through the transit area is calculated. It 
is equivalent to a point-to-point connection between two terminals. Parameters 
can be configured for this connection like a physical interface, such as sending a 
hello-timer. 
A “logic channel” is provided for multiple routers running OSPF that forwards 
messages between two ABRs. Since the destination addresses of the protocol 
messages are not these ABRs, the messages are transparent to them...

436CHAPTER 29: CONFIGURING OSPF
■dead-timer: 40 seconds
Configuring 
AuthenticationOSPF supports simple text authentication and MD5 authentication between 
adjacent routers.
Perform the following configurations in interface view.
Ta b l e 502   Configure Authentication
By default, the interface does not authenticate OSPF packets. 
The maximum length of a password for plain text authentication is 8 characters 
and for a MD5 string authentication the maximum length of the password is 16 
characters. The...