Principles of DIS election on a broadcast network on an S series switch


Q: What are the principles of DIS election on a broadcast network?
A: For S series switches supporting IS-IS, the IS where the interface with the highest Designated Intermediate System (DIS) priority resides is elected as the DIS on the same network segment. If interfaces have the same DIS priority, the IS where the interface with the largest MAC address resides is elected as the DIS. The DIS priority of an interfaces can be configured using the isis dis-priority priority-value command. A greater priority value indicates a higher priority.

Other related questions:
Prohibit DHCP broadcast packets on S series switch
ACL rules can be configured on S series switches (except S1700 switches) to deny DHCP broadcast packets on specified interfaces. For example, you can deny DHCP broadcast packets on GE0/0/1 as follows: 1. Create advanced ACL 3001 and configure a rule to deny DHCP broadcast packets. [Huawei] acl 3001 [Huawei-acl-adv-3001] rule deny udp destination-port eq 67 source-port eq 68 //Configure an ACL rule to deny DHCP broadcast packets. [Huawei-acl-adv-3001] quit 2. Configure the traffic classifier tc1 to classify packets that match ACL 3001. [Huawei] traffic classifier tc1 [Huawei-classifier-tc1] if-match acl 3001 [Huawei-classifier-tc1] quit 3. Configure the traffic behavior tb1 to deny packets. [Huawei] traffic behavior tb1 [Huawei-behavior-tb1] deny [Huawei-behavior-tb1] quit 4. Define a traffic policy and associate the traffic classifier and traffic behavior with the traffic policy. [Huawei] traffic policy tp1 [Huawei-trafficpolicy-tp1] classifier tc1 behavior tb1 [Huawei-trafficpolicy-tp1] quit 5. Apply the traffic policy to GE0/0/1. [Huawei] interface gigabitethernet 0/0/1 [Huawei-GigabitEthernet0/0/1] traffic-policy tp1 inbound [Huawei-GigabitEthernet0/0/1] quit

Why is the setup of an OSPF neighbor relationship between S series switches on a broadcast network slow
On a broadcast network, when two devices establish a 2-Way OSPF neighbor relationship, they elect the DR and BDR. Generally, the DR and BDR are elected after the Waiting timer expires, and the default value of the Waiting timer is 40s. Therefore, the setup of a Full OSPF neighbor relationship requires about 1 minute. Advertising a route to a loopback interface is useless. This is because a loopback interface cannot connect to a physical network, and traffic to a network segment cannot be routed to a loopback interface.

How does an S series switch elect an IGMP querier
When a host subnet is connected to the interfaces on multiple devices, to avoid data conflict, only one interface is allowed to send Query messages. This interface is the querier. The other interfaces running IGMP can receive the IGMP messages in this subnet. In IGMPv1, the querier is elected by a multicast routing protocol such as PIM. In IGMPv2 and IGMPv3, the switch interface with the lowest IP address acts as the querier.

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