LSA Types 4 and 5, and External Route Types 1 and 2
OSPF allows for two types of external routes, aptly named types 1 and 2. The type determines whether only the external metric is considered by SPF when picking the best routes (external type 2, or E2), or whether both the external and internal metrics are added together to compute the metric (external type 1, or E1). When an ASBR injects an E2 route, it creates a type 5 LSA for the subnet. The LSA lists the metric. The ASBR then floods the type 5 LSA throughout all areas. The..
Multiple Spanning Trees: IEEE 802.1s
IEEE 802.1s Multiple Spanning Trees (MST), sometimes referred to as Multiple Instance STP (MISTP) or Multiple STP (MSTP), defines a way to use multiple instances of STP in a network that uses 802.1Q trunking. The following are some of the main benefits of 802.1s: ■ Like PVST+, it allows the tuning of STP parameters so that while some ports block for one VLAN, the same port can forward in another VLAN. ■ Always uses 802.1w RSTP, for faster convergence. ■ Does not ..
Enhanced IGRP is enabled on a per-network basis. Eventually, it will be enabled on a per-subnet basis. Enhanced IGRP begins sending hello on all the interfaces in the specified networks. If a network is not specified under the Enhanced IGRP process, Enhanced IGRP will not send packets, nor will it include that network in Enhanced IGRP updates. In Figure 8-7, to enable Enhanced IGRP for network 10.0.0.0 but not for 131.108.0.0, the configuration would be as follo..
Logging Unauthorized SNMP Attempts
Use the following commands to configure your router to log unauthorized SNMP requests: Router#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)#access-list 99 permit 172.25.1.0 0.0.0.255 Router(config)#access-list 99 permit host 10.1.1.1 Router(config)#access-list 99 deny any log Router(config)#snmp-server community ORARO ro 99 Router(config)#snmp-server community ORARW rw 99 Router(config)#end Router# If you are concerned ..
OSPF defines an ASBR as a router that redistributes routes into OSPF from some other routing source. When redistributing the routes, the ASBR creates a Type 5 External LSA for each redistributed subnet, listing the subnet number as the LSID and listing the mask as one of the fields in the LSA. The LSA also lists the ASBR’s RID as the advertising router and a cost metric for the route. For the purposes of route summarization, you can think of a Type 5 LSA as working much lik..
