HSRP

[bava_ccna]

Hi,

I have some questions about HSRP

1# what is HSRP

2# what is the use of HSRP?

3# why do we need it

4# Explain it with examples

any help is appreciated

Bava

[bvsnarayana03]

HSRP is used for redundancy of devices & configured on interface attached to ethernet. In HSRP only one device is active at a time however you can make them work in load-balancing with some modifications.

Lets say you have 2 routers to reach the other end of WAN. Ideally you have gateway address on hosts as router IP address. But when you have 2 routers, which IP will you assign on hosts as default gateway. So HSRP provides a solution by providing a single virtual mac-address to the 2 devices. With this you can create a Virtual IP under each router interface & this virtual IP will be the gateway for all hosts. So when a pc sends pkt to virtual IP, its recvd by the router which is active in configuration & that router fwd the pkt further.

[serajuds05]

with hsrp, troubleshooting is made easier by taking out any of the routers providing the WAN link and still have service to the local hosts.

[sdoremus33]

1# what is HSRP: HSRP is HA solution that uses a virtual mac-address and ip address that each router uses Ex: Router a and Router B are connected to the same subnet lets ay 10.10.10.x where RtrA:.1 and B is .2 the client will use .3 which is the ip address of the Virtual HSRP router.

2# what is the use of HSRP? HSRP again is used in HA environments it is used for redundancy in the event one router link goes down

Ex: HSRP uses multicast address 224.0.0.3 I belive for link detection(hertbeat) every 5 seconds the multicast address polls each router where 1 is tehe active and 2 is the standby if after 3 successfull polls the devuce is considered down and the other(standby assumes the roll of the primary link or the GW (nect hop) for cflient compputers

3# why do we need it: Again this is used for redundancy in HA environments use it at depending on your companies needs

4# Explain it with examples:

Agaim another example is this

typically you have two routers obviouslly on same subnet ex 10.10.10.x network where rtr a is .1 and b is .2 they are considered primary and standby, there is a VR that has an address of .3 and a MAC of 00-00-00-12. Inthe config asll you do is under the Ethernet interface facing lan you add the following

cfgt

interface eth0/0

ip addr

standby 1 ip addr

standby 1 authent ""

standby 1 preempt 1

standby timers 5 15

again this is every 5 sec and polls 3 consecutive times then the link is down

simply do the same for rtrb with app ipaddress. HTH

[sdoremus33]

To make more clear

under each router (a,b)

Ex:

config t

interface ethernet0/0 -> Lan facing interface

ip addr 10.10.10.1 255.255.255.0

standby 1 ip address 10.10.10.3 --> IP address of VR

standby 1 preempt

standby 1 priority 100 -> The higher priority in the config is the active router

standby 1 authentication ""

standby 1 timers 5 15

Remember the devices (pri,standby) are polled every 5 sec and after the third attempt the device is ano longer active- until comes back online.

So all you need to do is add the config to (rtrb> and your on your way. HTH