This topic describes the basic concept of IP over DCC.
The IP over DCC protocol follows the TCP/IP protocol and is applied to control remote NEs through the Internet. For the IP over DCC protocol, the D bytes (D1-D3 by default) of the overhead are used for communication. Huawei optical equipment supports dynamic and static routing.
The open shortest path first (OSPF) protocol is a dynamic routing protocol based on the link state. The NEs update the route table of each NE dynamically by using the OSPF protocol. The OSPF protocol divides an autonomous domain into different areas so that routes are updated within an area or between areas. Normally, the gateway NE (GNE) and all the non-gateway NEs (non-GNEs) managed by it must be within the same OSPF area.
Supposing that all routers in a large-scale network run OSPF, the LSDB becomes extremely large and occupies a great amount of memory with the increase in routers and continuous expansion of the network size. This may complicate the SPF algorithm operation and leads to router overload.
Network expansion also causes an increased probability of topological changes, which make the network more often confronted with "turbulence". Meanwhile, the bandwidth utilization of the network is reduced because a large number of OSPF packets are transmitted on the network. In addition, every topological change causes all routers on the network to recalculate routes.
The OSPF protocol resolves the preceding problem by dividing the AS into different areas.
Logically, areas are router groups in the AS, and each area is uniquely identified by an area ID. At the border of an area resides a router, rather than a link. A network segment (or a link) belongs only to one area; that is, each port running OSPF must specify explicitly to which area it belongs.
After an OSPF network is divided into different areas, not all areas are equal. Generally, Area 0 is called the backbone area. The backbone area is responsible for forwarding the inter-area routes. The routing information between the non-backbone areas must be forwarded through the backbone area.
A stub area is a special area where the ABRs do not flood the received routes outside the AS. In a stub area, the routing table size on routers and the routing information in transmission are reduced.
A stub area is an optional configuration, but not all areas can be configured as stub areas. Generally, a stub area is a non-backbone area with only one ABR and is located at the AS boundary.
To ensure reachability to a destination outside the AS, the ABR in the stub area originates a default route and advertises it to the non-ABR routers in the stub area.
Note the following when configuring a stub area:
NSSAs are defined in much the same manner as existing stub areas. An NSSA does not import AS-external-LSAs (Type-5 LSAs). The ASBR in the NSSA originates Type-7 LSAs and advertise these LSAs only throughout the NSSA. When Type-7 LSAs reach the ABR of the NSSA, the ABR translates them into AS-external-LSAs (Type-5 LSAs) and floods them to the other areas. The ABR responsible for translating LSAs is also called the translator.
Area route aggregation is a process wherein an ABR aggregates routes with the same prefix and advertises only one aggregated route to other areas. This process is also known as ABR aggregation.
The area route aggregation process is described as follows: An ABR generates Type-3 LSAs by network segment and sends the LSAs to other areas. Specifically, the ABR advertises only one aggregated LSA to other areas, instead of all LSAs on a network segment. This method reduces routing traffic transmitted between areas and the routing table size, and as a result less system resources are occupied.
Proxy address resolution protocol (ARP) enables NEs on the same network segment but different physical networks to communicate with each other.
For a visit between the NEs on the same network segment, the source NE sends ARP broadcast packets to address the route to the sink NE. As the source and sink NEs are on different physical networks, the sink NE cannot receive MAC-layer broadcast packets from the source NE. Therefore, an ARP proxy NE is required. The NE with the proxy ARP function enabled checks the routing table after sensing the ARP broadcast packet. If the routing table contains the destination address that the ARP broadcast packet looks for, the NE returns an ARP spoofing packet, enabling the NE that sends the ARP broadcast packet to consider that the MAC address of the NE returning the ARP spoofing packet is the MAC address of the destination NE. The packet that is to be sent to the destination NE is first sent to the NE with the proxy ARP function enabled and then forwarded to the destination NE.