HSRP Interview Questions and Answers
HSRP stands for Hot Standby Router Protocol. It is a Cisco proprietary protocol that allows two or more routers to work together to present the appearance of a single virtual router to hosts on a LAN. This is done by sharing a virtual IP address and by maintaining consistency of routing information. In the event of a failure of the active router, a standby router takes over, ensuring that hosts on the LAN always have a valid default gateway.
HSRP routers use hello messages to communicate with each other and to determine the active router. The active router is the router with the highest priority, and if multiple routers have the same priority, the router with the highest IP address is chosen.
The virtual MAC address of an HSRP group is the MAC address that is associated with the virtual IP address of the group. This virtual MAC address is used by hosts on the LAN to communicate with the virtual router.
When a host sends a packet to the virtual IP address, the packet is actually sent to the virtual MAC address, which is then forwarded to the active HSRP router. The active router then forwards the packet to its destination using its own MAC address.
The virtual MAC address for HSRP is in the format of 0000.0C07.ACxx , where xx is the HSRP group number in hexadecimal format.
For example, if the HSRP group number is 10, the virtual MAC address would be 0000.0C07.AC0A.
It's important to note that each HSRP group will have a unique virtual MAC address.
HSRP (Hot Standby Router Protocol) uses UDP (User Datagram Protocol) as the transport protocol for its communication. Specifically, HSRP uses UDP port 1985 to send and receive messages between routers in the same HSRP group.
UDP is used because it is a connectionless, fast and lightweight protocol, which makes it well suited for the type of control messaging used by HSRP. It is also less reliable than TCP, which allows for faster failover in case of a problem with the active router.
HSRP routers use hello messages to communicate with each other and to determine the active router. The active router is responsible for forwarding packets sent to the virtual IP address, and for sending gratuitous ARP messages to update the ARP caches of hosts on the LAN.
It's important to note that although HSRP uses UDP as its transport protocol, it is not a routing protocol, it is a redundancy protocol. It's used to provide redundancy and failover capability in a LAN environment.
In HSRP (Hot Standby Router Protocol), the source IP address of a hello message is the IP address of the router sending the message and the destination IP address is the multicast IP address 224.0.0.2.
When a router first joins an HSRP group, it sends a hello message to the multicast IP address 224.0.0.2 on UDP port 1985. This multicast IP address is used by all routers in the same HSRP group to exchange hello messages.
The destination IP address of a hello message is the multicast IP address 224.0.0.2, which is a reserved multicast address that is used by HSRP routers.
The hello message contains information about the HSRP group, including the virtual IP address, the virtual MAC address, and the priority of the router. This information is used by other routers in the same HSRP group to determine the active router, and to update their own HSRP configuration.
It's important to note that the multicast IP address 224.0.0.2 is only used by HSRP routers and it doesn't reach any other device on the network.
Yes, it is possible to configure HSRP (Hot Standby Router Protocol) on a multilayer switch.
A multilayer switch is a device that can perform both switching and routing functions. It is typically capable of running routing protocols, as well as providing switching capabilities for LANs.
In HSRP (Hot Standby Router Protocol), the default hold time is 10 seconds and the default hello time is 3 seconds.
The hold time is the amount of time that a router will wait before considering a neighbor router as down. It's the time that a router will wait after not receiving a hello message from its neighbor before considering it down.
The hello time is the amount of time between hello messages that are sent by the active router. Hello messages are used by HSRP routers to communicate with each other and to determine the active router.
The default hold time of 10 seconds and the default hello time of 3 seconds are recommended values for most networks, but these values can be adjusted to meet the specific needs of a network. For example, if your network is large and it takes longer for hello messages to propagate, you might want to increase the hello time.
It's important to note that the hold time and the hello time values should be the same among all routers in an HSRP group. If the values are different between routers, it may cause issues with the HSRP group.
is the original version of the protocol, which was first introduced by Cisco. It uses multicast IP address 224.0.0.2 and UDP port 1985 for communication between routers in the same HSRP group. HSRP version 1 supports a maximum of 100 groups per interface and up to 1000 groups per router.
is an extension of version 1 that was introduced to address some limitations of version 1. It uses multicast IP address 224.0.0.102 and UDP port 1985 for communication between routers in the same HSRP group. HSRP version 2 supports a maximum of 100 groups per interface and up to 1000 groups per router.
HSRP version 2 uses a different multicast IP address which is 224.0.0.102 compared to 224.0.0.2 in version 1
HSRP version 2 supports authentication of hello messages, which provides added security by preventing unauthorized routers from joining the HSRP group.
HSRP version 2 supports a different type of authentication, called MD5 authentication, which is more secure than the simple text authentication used in version 1.
It's important to note that HSRP version 2 is backwards compatible with version 1, which means that routers running version 2 can communicate with routers running version 1.
It's also recommended to use the latest version of HSRP, as it provides more security and flexibility than the older version.
In HSRP (Hot Standby Router Protocol), there are several states that a router can be in depending on its role and the status of the group. The main states are:
: The router starts in this state when it is first configured for HSRP. In this state, the router is not yet aware of any other HSRP routers on the network, and it is not sending or receiving any HSRP messages.
: The router enters this state after it has sent an initial hello message. In this state, the router is listening for hello messages from other routers in the same HSRP group.
: If the router receives a hello message from another router in the same HSRP group, it enters this state. In this state, the router is sending and receiving hello messages, and it is aware of the other routers in the group.
: In this state, the router has a lower priority than the active router, and it is not forwarding any packets sent to the virtual IP address. It is ready to take over as the active router in case the active router fails.
: In this state, the router is the active router, and it is forwarding packets sent to the virtual IP address. It also sends gratuitous ARP messages to update the ARP caches of hosts on the LAN.
: If the HSRP configuration is removed from a router or if the router is rebooted, it goes to this state.
It's important to note that these states are not mutually exclusive. A router may transition between these states depending on the status of the group and the role of the router.
Priority Mismatch, VIP configuration on the standby router, Reachability.
Use below command to configure HSRP- exp 10.10.10.3 and 10.10.10.2 is the ip address of both device and virtual ip – 10.10.10.1
R1#show standby
FastEthernet0/0 - Group 1State is Active2 state changes, last state change 00:23:53
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