Challenges in Multi-Channel Access Networks

Challenges in multi-access networks: in multi-access networks, more than two devices are connected to the same shared media. An Ethernet LAN is a type of broadcast Multi-Channel Access Network. Because all devices in the network will see all broadcast frames, it belongs to the broadcast network.
OSPF defines five network types: l point-to-point www.2cto.com l broadcast Multi-Channel Access l non-broadcast Multi-Channel Access (NBMA) l point-to-point l virtual link
Multi-channel access networks pose two challenges to the LSA Flooding Process of OSPF: 1. Create a multilateral adjacent relationship, and each pair of routers has an adjacent relationship. 2. massive flooding of LSA (link status announcement.
Creating an adjacent relationship between each pair of vrouters in the network produces unnecessary adjacent relationships. This will cause a large number of LSAs to be transmitted between routers in the network. For any number of routers in a Multi-Channel Access Network (expressed as n), there will be n (n-1)/two adjacent relationships. However, as the number of routers in the network increases, the number of adjacent links increases dramatically.
The LSA flood link status router will flood its link status packets during OSPF initialization and topology changes. In a multi-channel access network, the traffic during this flooding process may become very large.
Solution: A Router (DR) is used to manage the number of adjacent links and the LSA flooding in a multi-channel access network ). (It can be said that a person is elected in the room, and the person asks each person for their names one by one, and then gives them one-time notice to all people .) A dr and a BDR are selected for the vro in the Multi-Channel Access Network. DROther only establishes a completely adjacent relationship with the DR and BDR in the network. This means that DROther does not need to flood LSA to all vrouters in the network. Instead, send the LSA to DR and BDR using the multicast address 224.0.0.6 (ALLDRouters-all DR vrouters. Www.2cto.com DR/BDR election process (DR/BDR election will not happen in point-to-point networks)
The DR/BDR election process follows the following conditions: 1. DR: Router with the highest OSPF interface Priority 2. BDR: Router with the second highest OSPF interface Priority 3. if the OSPF interface has the same priority, the router ID is the highest.
DROther only establishes a completely adjacent relationship with DR and BDR, but it also establishes an adjacent relationship with any other DROthers in the network. This means that all DROther routers in the Multi-Channel Access Network will still receive Hello packets from all other DROther routers. When the two DROther routers form an adjacent relationship, the adjacent status is displayed as 2WAY. Use show ip ospf neighbor to quickly view DR, BDR, DROther, and 2WAY. Use show ip ospf interface to view detailed DR and BDR Information
DR/BDR election schedule once selected, DR status will be maintained until one of the following conditions occurs: l DR fault. L The OSPF process on DR fails. L multiple access interfaces on DR fail. If DR fails, BDR will take over the DR role and then elect a new BDR. Add a new vro to the network. If a new router is added to the network after DR and BDR are selected, the OSPF interface priority or router ID of the new router is higher than that of the current DR or BDR.
The former DR will not regain its position as a DR after returning to the network. Www.2cto.com if the BDR fails, a new BDR will be selected between DRother. How do you ensure that the required routers win the DR and BDR elections? No further configuration is required. There are two solutions: l first start DR, then start BDR, and then start all other routers; l disable interfaces on all routers, then run the no shutdown command on DR, then run the command on BDR, and then run the command on all other routers.
OSPF interface priority because DR becomes the distribution center of LSA, it must have sufficient CPU and storage performance to bear this responsibility. Instead of relying on the router ID to determine the DR and BDR results, it is better to use the ip ospf priority interface command to control the election. Router (config-if) # ip ospf priority {0-255} OSPF default route redistribution R1 # conf t R1 (config) # ip route 0.0.0.0 0.0.0 loopback 1 R1 (config) # router ospf 1 R1 (config-router) # default-information originate route table output information: O * E2 0.0.0.0/0 [110/1] via 192.168.10.10, 00:05:34, Serial0/0/1
O indicates the OSPF learned route E2 indicates that this route is an OSPF 2nd class external route. OSPF external routes are classified into the following two types: Class 1 external routes (E1) and Class 2 external routes (E2 ). The difference between the two types is that the OSPF overhead of the route is calculated differently on each router. L when the E1 route is transmitted throughout the OSPF region, OSPF accumulates the overhead of the route. L the overhead of the E2 route is always an external overhead, but it is irrelevant to the internal overhead to the route.
To fine-tune the OSPF www.2cto.com reference bandwidth, you can use the OSPF command auto-cost reference-bandwidth to modify the reference bandwidth to meet the requirements of these faster links. R1 (config-router) # auto-cost reference-bandwidth "1 ~ The unit of 4294967 is Mbits.
To modify the OSPF interval, run the following command to manually modify the OSPF Hello interval and Dead interval: Router (config-if) # ip ospf hello-intervalseconds // how many seconds at which the Hello message is sent? Router (config-if) # ip ospf dead-intervalseconds // how many seconds after the Hello message is received?