Destination IP addresses of packets of different network types sent by OSPF interfaces on S series switches

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Destination IP addresses of packets of different network types sent by S series switches supporting OSPF are as follows:
Hello packets
On a broadcast, P2MP, or P2P network, Hello packets are sent to the manycast IP address 224.0.0.5. On a virtual link, Hello packets are sent to the other end of the virtual link. On an NBMA network, Hello packets are sent to neighbors in unicast mode.

DD, LSR, and LSU packets
On broadcast, P2MP, and NBMA networks, DD, LSR, and LSU packets are sent to the IP addresses of neighbors in unicast mode. On P2P networks, DD, LSR, and LSU packets are sent to the IP address 224.0.0.5.

LSAck packets
On a P2P network, LSAck packets are sent to the IP address 224.0.0.5.
On P2MP and NBMA networks, LSAck packets are sent to neighbors in unicast mode.
On a broadcast network, LSAck packets are transmitted in multicast mode. If sent by the DR or BDR, the packets are transmitted to 224.0.0.5; otherwise, the packets are transmitted to 224.0.0.6.

Other related questions:
MTU value of OSPF DD packets sent by S series switches
According to RFC 2328, the value of the Interface MTU field in a DD packet is the MTU value of the link (if the link is a virtual link, the value is 0). When a device receives a DD packet with an Interface MTU value larger than the MTU value in DD packets sent by the device, the device drops the DD packet and the neighbor status stays Exchange Start. On an S series switch supporting OSPF, you can run the ospf mtu-enable command in an interface view to check the MTU value in received DD packets. By default, OSPF does not check the MTU value in a DD packet. If the MTU match check is not performed, LSDBs of the two ends can be synchronized and the OSPF neighbor relationship can enter the Full state with the MTU values configured on the two ends varying slightly.

Can an S series switches forward a packet if both the source and destination IP addresses of the packet are multicast addresses
The S5710-C-LI or S5700SI drops packets whose source and destination IP addresses are both multicast addresses. Other switches broadcast such packets in a VLAN.

Can an OSPF neighbor relationship be established if the network types of the two S series switches are different
Question: Can a Full neighbor relationship be established if the network types of the two ends of an OSPF link are different? Answer: Yes. For example, two devices are interconnected through an Ethernet link. On one end of the link, the default broadcast network type is adopted. The other end is configured as OSPF peer-to-peer (P2P). Neighbor relationship can be established between these two devices, which reach the Full state by exchanging their Link State Databases (LSDBs). However, no route can be learned because OSPF devices need LSDBs to construct a Shortest Path Tree (SPT). The LSDBs, however, are problematic. That is, the link-state advertisements (LSAs) generated by one end consider the peer a broadcast neighbor, while the other end considers its peer a P2P neighbor. Therefore, no SPT can be constructed correctly and the Shortest Path First (SPF) algorithm cannot calculate the right routes either.

Commands for checking OSPF network type faults on S series switches
You can run the following commands on an S series switch supporting OSPF to check information about OSPF network type faults: display ospf interface The command output displays information about an OSPF interface. ospf network-type This command is used to set the network type of an OSPF interface.

Relationship among the media type, link type, and network type of OSPF on S series switches
Question: What are OSPF media type, link type, and network type? What is the relationship among them? Answer: OSPF media type, link type, and network type are described as follows: Media type: indicates types of physical links, including GigabitEthernet and Ethernet links. Link type (in LSAs): The link type in an LSA is set based on the ospf network-type setting, as defined in RFC 2328. On a point-to-point (P2P) network, the link type is point-to-point. If a device is connected to a transmission network, the link type is transit. If a device is connected to a stub network, the link type is stub. If a device is connected to a virtual link, the link type is virtual. Network type: The OSPF network type can be configured as required regardless of physical media. Currently, OSPF network types include P2P, broadcast, NBMA, and P2MP. Relationship among the media type, link type, and network type: The default OSPF network type depends on the media type, and the OSPF network type determines the link type in an LSA.

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