Implementing Network Redundancy Flashcards
What is HSRP?
HSRP is a Cisco proprietary protocol that was developed to allow several multilayer switches or routers to appear as a single gateway IP address.
Hosts on IP networks usually only have a single IP address that is configured as their default gateway. HSRP allows two physical routers to work together in an HSRP group to provide a virtual IP address and an associated virtual MAC address.
End Hosts and FHRP, how does it work? (HSRP)
The end hosts use the virtual IP address as their default gateway and learn the virtual MAC address via ARP. One of the routers in the group is active and responsible for the virtual addresses. The other router is in a standby state and monitors the active router.
If there is a failure on the active router, the standby router assumes the active state. The virtual addresses are always functional, regardless of which physical router is responsible for them. The end hosts are not aware of any changes in the physical routers.
Understanding HSRP
HSRP is an FHRP that allows for transparent failover of the first-hop IP device (default gateway). Most IP hosts have an IP address of a single router configured as the default gateway. When you use HSRP, the HSRP virtual IP address is configured as the default gateway for the host instead of the IP address of the router.
HSRP Characteristics…
The following are characteristics of HSRP:
HSRP defines a group of routers—one active and one standby.
Virtual IP and MAC addresses are shared between the two routers.
To verify the HSRP state, use the show standby command.
HSRP is Cisco proprietary. VRRP is an open standard.
HSRP Active Router - Characteristics
The HSRP Active route has the following characteristics:
Responds to default gateway ARP requests with the virtual router MAC address
Assumes active forwarding of packets for the virtual router
Sends hello messages
Knows the virtual router IP address
HSRP Standby Router- Characteristics
The HSRP Standby route has the following characteristics:
Sends hello messages
Listens for periodic hello messages
Assumes active forwarding of packets if it does not hear from the active router
HSRP vs VRRP
HSRP is a Cisco proprietary protocol, and VRRP is a standard protocol. Beyond this fact, the differences between HSRP and VRRP are very slight.
HSRP Group
An HSRP group is a set of HSRP devices that emulate a virtual router.
Use the following command to configure the HSRP group:
Router( config-if)# standby group number ip ip-address
By default, the group number would be set to group 0
With HSRP version 1, a group number can be any integer between 0 and 255.
All routers in an HSRP group exchange hello messages.
Roles of routers in the HSRP group are elected based on the exchange of hello messages.
HSRP active and standby routers send hello messages to the multicast address 224.0.0.2, UDP port 1985.
HSRP Commands
show standby
show standby brief
Both useful commands
Also useful to have premempt enabled for deterministic routing and also to consider delay minimum
