Saturday, May 10, 2014

Hot Standby Router Protocol (HSRP) – Routing Redundancy

Hot Standby Router Protocol (HSRP) – Routing Redundancy
1.     It is a Cisco Proprietary
2.     It enables a set of router interfaces to present the appearance of a single virtual router or default gateway to the hosts on a LAN.
3.     It provides a virtual Media Access Control (MAC) address and an IP address that is shared among the LAN network.
4.     The virtual router does not exist; it represents the common target for routers that are configured to provide backup to each other. 
5.     One of the routers is selected to be the active router and another to be the standby router, which takes control of the group MAC address and IP address should the designated active router fail.

The standby ip interface configuration command activates HSRP on a Layer 3 interface. Devices running HSRP send and receive multicast UDP-based hello packets to detect router failure and to designate active and standby routers.
The switch supports HSRP MAC addresses for up to 16 unique HSRP groups. Because each group address can be used on up to 16 Layer 3 interfaces, the maximum number of HSRP interfaces is 256. Cisco recommends to use no more than 64 HSRP interfaces due to CPU utilization.

Default HSRP Configuration
HSRP groups – None configured
Standby group number – 0
Standby MAC address – 0000.0c07.acXX, where XX is the HSRP group number
Standby priority – 100
Standby delay 0
Standby track interface priority 10
Standby hello time – 3 seconds
Standby holdtime – 10 seconds

HSRP Configuration Guidelines and Limitations
There are three types of interfaces that can be used to configure HSRP
1.     Routed port – a physical port configured as a Layer 3 port by entering the no switchport interface configuration command.
2.     SVI – a VLAN interface created by using the interface vlan vlan_id global configuration command and by default Layer 3 interface.
3.     Etherchannel port channel in Layer 3 mode – a port-channel logical interface created by using the interface port-channel port-channe-number global configuration command and binding the Ethernet interface into the channel group.
All Layer 3 interfaces must have IP addresses assigned to them.
An interface can belong to multiple HSRP groups, and the same HSRP group can be applied to different interfaces.

Following the steps below to create or enable HSRP on a Layer 3 interface:
1.     Enter global configuration mode.
2.     Enter interface configuration mode, and enter the Layer 3 interface on which you want to enable HSRP.

3.     Create the HSRP group using its number and virtual IP address. standby [group-number] ip [ip-address [secondary]]

Reference:
http://www.cisco.com/en/US/docs/switches/lan/catalyst3550/software/release/12.1_19_ea1/configuration/guide/swhsrp.html

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