What is HSRP ?

So, it has been awhile since I’ve actually put some technical stuff out on my blog. Well, I interviewed a guy today and he was asked about HSRP. Essentially he was asked…what can you tell me about HSRP? The guy didn’t know. So this is for you, Mr. Interview Guy. It’s something that you need to know when you interview for a Network Engineer position where the IT shop is mostly Cisco.

HSRP stands for Hot Standby Router Protocol. However, it is not hot nor is it a routing protocol. It is used for standby though. It’s not hot because, I just don’t consider technical stuff hot. It’s also not a routing protocol as it doesn’t advertise routes. So who the heck came up with the name? Some geeky router guy at Cisco back in the day I guess.

Now for the technical stuff. HSRP is a redundancy based protocol (the standby part) and is essential when designing highly available networks. (HA for guys in the trenches like me.) The design typically includes two routers (and can be more) and provides for a redundant default gateway. An interface is usually built on each router, each interface gets its own IP Address, and each interface also has a standby IP address in that same subnet defined. That standby is the same on each router. That standby IP address is the default gateway used by devices that are members of the network on that interface.  Multicast traffic is the method that keeps the two interfaces checking on each other and if one member goes away, the other member picks up the slack. Because you have more than one interface, one interface in the group has to be assigned priority and that’s the interface most traffic will use until there is a reason to failover to the other.  The standards based version is called VRRP (virtual router redundancy protocol). VRRP and HSRP do not like each other so you have to choose one or the other. Obviously if you don’t have Cisco, you will be using VRRP.

A config may look like this

Router Hot

Interface FastEthernet 0/0
ip address 192.168.1.2 255.255.255.0
standby 1 ip 192.168.1.1
standby 1 preempt
standby 1 priority 150

Router Not

Interface FastEthernet 0/0
ip address 192.168.1.3 255.255.255.0
standby 1 ip 192.168.1.1
standby 1 preempt
standby 1 priority 100

 Hope that helps Mr. Interview Guy!

 

(source: Internet)

2 thoughts on “What is HSRP ?

  1. Minh Anh says:

    Ui’ anh ui, trinh` tieng anh cua anh len vay roi ha? thi duoc may chuc cham roi?😛 lay vo chua heo?

    • valentinie says:

      Cuối năm nay tôi cưới. Cô đã đi đâu chưa? Ở nhà là không được vắng mặt đâu nhé.😛

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