Introduction to HSRP Routing Protocol

HSRP is also a type of routing protocol. So what is the role of this protocol? What are the features? In this article, we will introduce some concepts and structures of this Protocol in detail. With the increasing popularity of the Internet, people are increasingly dependent on the network. At the same time, they have put forward higher requirements on Network stability. People naturally think of a device-based backup structure, just like using a dual-hard disk structure on the server to improve data security ｡

Vro is the core and heart of the entire network. If a fatal fault occurs on the vro, it will paralyze the local network. If it is a backbone router, the impact scope will be greater, therefore, hot backup is an inevitable choice to improve the network robustness (robust). When a router cannot work at all, all of its functions are taken over by another backup router in the system until the faulty router returns to normal. This is Cisco's hot wait routing protocol (HotStandbyRouterProtocal, HSRP routing protocol) the problem to be solved ｡

I. Overview of HSRP Routing Protocol

The condition for implementing the HSRP routing protocol is that there are multiple routers in the system and they form a "hot wait group", which forms a virtual router, only one vro in A group is active and forwards data packets. If the active vro fails, a waiting vro is selected to replace the active vro, however, in the view of hosts in the network, the virtual router has not changed. Therefore, the host remains connected and is not affected by the fault, in this way, the problem of vro switching is better solved. To reduce the data traffic of the network, After configuring the active router and waiting for the router, only the active router and the waiting router regularly send the HSRP Route Protocol packet. If the active router fails, wait for the router to take over as the active router. If the active router fails or becomes the active router, select another vro as the waiting vro ｡

In a Specific Lan, multiple hot wait groups may coexist or overlap. Each hot wait group imitates a virtual router, it has a Well-known-MAC address and an IP address. This IP address, the interface address of the vro in the group, and the host is in the same subnet, but not the same. When multiple hot wait groups exist on a LAN, the host is distributed to different hot wait groups, so that the load can be shared ｡

Ii. HSRP Route Protocol packet format

In the hot wait group, the router regularly broadcasts status information of different types of data packets. The protocol runs on UDP and the port number is 1985. The destination address is 224.0.0.2, TTL is marked as 1. The source address of the data packet is the actual IP address of the sender router, rather than the virtual address, which can be used to mark different routers ｡

Iii. vro status and status TRANSITION IN HSRP

In a hot wait group, each vro runs a simple state machine and switches to a different state through the current state and event triggering ｡

1. The initial status of HSRP when the routing protocol is started. The HSRP routing protocol is not running yet. Generally, this status is entered when the configuration is changed or the port is just started ｡

2. In this status, the vro does not determine the virtual IP address, nor does it see the authenticated HELLO Message from the active router. The router is still waiting for the HELLO message sent from the active router ｡

3. The vro in the listening status has obtained a virtual IP address, but it is neither an active router nor a waiting router. It has been listening for the HELLO packets sent from the active router and waiting for the router ｡

4. In this status, the vro regularly sends HELLO messages and actively participates in the active vro or waits for the election of the vro ｡

5. A waiting vro in this status is the next candidate active vro, which regularly sends HELLO messages ｡

6. A vro in the active state is responsible for packet forwarding. These packets are sent to the virtual MAC address of the group. It regularly sends HELLO packets. In addition, each vro has three timers, namely the active timer, the wait timer, and the call timer. status changes are caused by events, different events act on different States and may produce different actions, such as starting a timer or sending a message ｡

IV. Implementation of HSRP Routing Protocol in Campus Network

The Campus Network of East China Normal University is large in size and has a relatively large number of hosts accessing the Internet. It is equipped with 16 class C addresses. In order to ensure data security and broadcast storms and improve network performance, divide the campus network into 60 subnets. In the network center, Cisco's ipvst5509 is used as the central switch, and RSM is used as the router between VLANs, in addition, a Cisco7000 series router and RSM are used. Both support VLAN and HSRP routing protocol on VLAN. Each Virtual LAN has an HSRP routing protocol group. Logically speaking, the RSM of Cisco7010 and Cisco5509 has LAN interfaces on each virtual LAN and IP addresses are configured. A virtual address is also configured as the gateway of all hosts in the virtual LAN ｡