You just call out my name, and you know wherever I am
I’ll come running, oh yeah baby, to see you again
Winter, spring, summer, or fall
All you got to do is call and I’ll be there, yeah, yeah, yeah
You’ve got a friend

Whenever I see Hot Standby Router Protocol (HSRP), it always reminds me of a song. As what James Taylor said, “You’ve Got a Friend.” If you already know what HSRP is, you might’ve as well other things that make you remember what it does.

If you’re kinda new and trying to understand what this is, this is a good start as I will not make this topic complicated. Although there are lots of things to tackle with HSRP, we will stick with the basics and some links are provided below to further discuss other HSRP topics.

HSRP is not a router and definitely not a routing protocol. When I first studied HSRP, the first thing that came up in my mind is that this is a routing protocol like EIGRP, BGP, OSPF, or RIP but it isn’t as it does not affect the routing table.

HSRP is a Cisco proprietary redundancy protocol. One device will act as active and the other is passive. Once the active device is down, the passive device will take over. The active device will be responsible for handling the traffic of the VIP (virtual IP). Since the VIP is shared between these two devices, when the active device fails, traffic will failover to the standby device. However, keep in mind that pre-emption is not enabled by default.

HSRP ELECTION: HSRP PRIORITY

What is the criterion for becoming the active device? -> the configured priority. The higher the priority value, the better. You can configure the priority value from 0-255. What if you don’t configure the priority value? Then the default is 100. What if they have the same priority value? Then, the highest configured IP address will be the active device.

NICE TO KNOW:

• You can configure up to 255 HSRP groups. It is locally significant so you can use the same HSRP group number for all the VLAN interfaces. However, it is recommended to match the group number with the VLAN number to avoid confusion or configuration error.
• HSRP uses a virtual MAC address of 0000.0C07.ACxx where xx is the hex value of the HSRP group number. For example,

a. HSRP group number is 1, then the MAC address is 0000.0C07.AC01
b. HSRP group number is 100, then the MAC address is 0000.0C07.AC64

HSRP TOPICS:

• HSRP Versions
• HSRP and Object Tracking
• HSRP Lab Configuration
• HSRP States
• HSRP Authentication
• HSRP Troubleshooting
• VPC and HSRP

BGP Neighbor Adjacency States:

1. IDLE – This is normally can be seen if BGP is down / administratively down or just waiting for the next attempt. At this stage, no BGP incoming sessions are permitted.

My BGP is established between Culloden and Stirling sites and Culloden and Fyvie sites. But when I shut down s2/2 link between Culloden and Fyvie, my BGP went to IDLE state.

Culloden(config)#int s2/2
Culloden(config-if)#shut
Culloden(config-if)#end

2. CONNECT – This is when BGP starts to do the TCP connection (TCP three-way handshake). Either of the BGP neighbors will initiate the BGP session. Once completed, it jumps towards the OPENSENT state. However, if there is a problem, it goes to ACTIVE state.

3. ACTIVE – At this stage, TCP connection is completed but no BGP messages have been sent to the BGP neighbor yet. There are many reasons why BGP is stuck in ACTIVE state. Usually, there are configuration issues that stop the BGP connection from getting established. It can be a wrong AS, misconfigured local IP / peer IP address, authentication issues, and others.

. OPENSENT – BGP Open message is already been sent to the peer but not yet received to the other end. You won’t usually see BGP stuck in OPENSENT state. It will immediately toggle to OPENCONFIRM state and ESTABLISHED states.

5. OPENCONFIRM – BGP Open message and keepalive has been sent and received. It won’t take long until it goes to the ESTABLISHED state.

6. ESTABLISHED – Once all the BGP requirements of establishing neighbor adjacency are met, it goes to the ESTABLISHED state. You will see prefixes Once adjacency is established between BGP neighbors, they are going to start exchanging routing information.

Putting back my s2/2 link up, makes my BGP back to ESTABLISHED state:

Culloden(config)#int s2/2
Culloden(config-if)#no shut
Culloden(config-if)#end
Culloden#