D-Link DGS-3620-28TC-SI Product Manual - Page 192

xStack® DGS-3620 Series Managed Switch Web UI Reference Guide Type-7 LSA (Link State Advertisement) packets are used to import external routes into the NSSA. These packets can originate from NSSA ASBRs or NSSA ABRs and are defined by setting the P-Bit in the LSA type-7 packet header. Each destination network learned from external routes is converted into Type-7 LSA packets. These packets are specific for NSSA switches and the route information contained in these packets cannot leave the area unless translated into Type-5 LSA packets by Area Border Routers. See the following table for a better description of the LSA type-7 packet seen here. Figure 5-33 LSA Type-7 Packet Parameter Link State Packet Header Network Mask E-bit Forwarding Address TOS Metric External Route Tag Description This field will hold information concerning information regarding the LS Checksum, length, LS sequence number, Advertising Router, Link State ID, LS age, the packet type (Type-7), and the options field. The Options byte contains information regarding the N-Bit and the P-Bit, which will be described later in this section. The IP address mask for the advertised destination. The type of external metric. If the E-bit is set, the metric specified is a Type 2 external metric. This means the metric is considered larger than any link state path. If the E-bit is zero, the specified metric is a Type 1 external metric. This means that is comparable directly to the link state metric. Data traffic for the advertised destination will be forwarded to this address. If the Forwarding Address is set to 0.0.0.0, data traffic will be forwarded instead to the advertisement's originator. Yet, if the network between the NSSA ASBR and the adjacent AS is advertised in the area as an internal OSFP route, this address will be the next hop address. Conversely, if the network is not advertised as internal, this field should be any of the router's active OSPF interfaces. The Type of Service that the following cost is relevant to. The cost of this route. The interpretation of this metric depends on the external type indication (the E-bit above). A 32-bit field attached to each external route. This is not used by the OSPF protocol itself. The N-Bit Contained in the options field of the Link State Packet header, the N-Bit is used to ensure that all members of an NSSA agree on the area configurations. Used in conjunction with the E-Bit, these two bits represent the flooding capability of an external LSA. Because type-5 LSAs cannot be flooded into the NSSA, the N-Bit will contain information for sending and receiving LSA type-7 packets, while the E-bit is to be cleared. An additional check must 182