It cannot establish ospf peer because of the different of usg network type

Publication Date:  2012-10-17 Views:  423 Downloads:  0
Issue Description

Symptom :
1、 usg2100 BSR and AR 18 Router establish ospf, but it cannot be successful
2、 the two facilities use serial port to connect with each other
3、 the direct connection address can ping pass each other
4、 there is no problem with the ospf configuration of usg,  the configuration of peer end cannot get it, but client say the configuration of peer end has no problem. Our usg2100BSR is AR18 equipment before changing
Alarm Information
None.
Handling Process
We can find our equipment use the multicast mode to send out from the capturing packet information, but the peer end uses the unicast mode to send. The default network type of peer end is NBMA evidently.
Modify the network type of this end.
Modify to NBMA in the interface
interface Serial2/0/0
      ospf network-type nbma
Root Cause
1、 we analyse the problem by checking the configuration: but there is no problem

2、 view the state of ospf: but there is no problem

3、 analyse by capturing packet

4、 we can find our equipment use the multicast mode to send out from the capturing packet information, but the peer end uses the unicast mode to send. The default network type of peer end is NBMA evidently.
Suggestions
The explanation of the network type:
Broadcast type:when the link layer protocol is Ethernet、FDDI,OSPF default network type is Broadcast. In this network type: sending Hello message and all the message which is come from DR by the multicast type(224.0.0.5: it means the reservation IP multicast address of OSPF Router); sending LSU message by the multicast type(224.0.0.5: it means the reservation IP multicast address of DR), then DR sends this LSU message to 224.0.0.5; sending DD message、 LSR message and all the retransmission message by unicast type;
Sending LSAck message by multicast type (224.0.0.5) in the normal situation. When Router receives the repeated LSA or reaches the most long time to live which the LSA has been deleted, LSAck sends by unicast type.
NBMA(Non-Broadcast Multi-Access) type: when link layer protocol is frame relay、ATM or X.25, OSPF default network type is NBMA. It this network type: sending protocol message by unicast type (Hello message、DD message、LSR message、LSU message、LSAck message).
P2MP(point-to-multipoint) type:there is no link layer protocol is default considered Point-to-Multipoint type. This type must be changed by other network type. The common modus operandi is to make the not all connection NBMA change to point-to-multipoint network. In this network type :sending Hello message by multicast type(224.0.0.5), sending DD message、LSR message、LSU message、LSAck message by unicast type.
P2P(point-to-point)type: when the link layre protocol is PPP、HDLC and LAPB, OSPF default network type is P2P. In this network type : sending protocol message(Hello message、DD message、LSR message、LSU message、LSAck message) by multicast type(224.0.0.5).

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