hot standby routing protocol

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HOT STANDBY ROUTING PROTOCOL

PART I: SUMMARY

Hot Standby Router Protocol (HSRP) is a Cisco proprietary redundancy protocol

for establishing a fault-tolerant default gateway, and has been described in detail in RFC

2281.

The primary router with the highest configured priority will act as a virtualrouter

with a pre-defined gateway IP address and will respond to the ARP request from

machines connected to the LAN with the MAC address 0000.0c07.acXX where XX is thegroup ID in hex. If the primary router should fail, the router with the next-highest priority

would take over the gateway IP address and answer ARP requests with the same mac

address, thus achieving transparent default gateway fail-over. AHSRP Basics

Simulation visualizes Active/Standby election and link failover with Hello, Coup, ARP

Reply packets and timers.

HSRP is not a routing protocol as it does not advertise IP routes or affect

the routing table in any way.

HSRP has the ability to trigger a failover if one or more interfaces on the router godown. This can be useful for dual branch routers each with a single serial link back to

the head end. If the serial link of the primary router goes down, the backup router would

take over the primary functionality and thus retain connectivity to the head end.

HSRP uses the exchange of multicast messages to communicate a configured

priority with other routers in the samestandby group. The priority defines which router

will be the primary and which router(s) will be secondary in the group. The default

priority is 100; the router with the highest priority will be the primary for the group. If the

priorities are the same, the first router up becomes the primary. Any prioritization is then

based on the IP address. If a new router (at the same priority) joins, it doesn't bump the

current primary router, even if its IP address is higher; however, it can bump the current

standby router.

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http://en.wikipedia.org/wiki/Cisco_Systems,_Inc.http://en.wikipedia.org/wiki/Proprietary_protocolhttp://en.wikipedia.org/wiki/Default_gatewayhttp://tools.ietf.org/html/rfc2281http://tools.ietf.org/html/rfc2281http://en.wikipedia.org/wiki/Hexidecimalhttp://pre.visualland.net/view.php?cid=846&protocol=HSRP&title=1.%20HSRP%20basichttp://pre.visualland.net/view.php?cid=846&protocol=HSRP&title=1.%20HSRP%20basichttp://en.wikipedia.org/wiki/Routing_protocolshttp://en.wikipedia.org/wiki/Internet_Protocolhttp://en.wikipedia.org/wiki/Routinghttp://en.wikipedia.org/wiki/Head_endhttp://en.wikipedia.org/wiki/Head_endhttp://en.wikipedia.org/wiki/Routinghttp://en.wikipedia.org/wiki/Internet_Protocolhttp://en.wikipedia.org/wiki/Routing_protocolshttp://pre.visualland.net/view.php?cid=846&protocol=HSRP&title=1.%20HSRP%20basichttp://pre.visualland.net/view.php?cid=846&protocol=HSRP&title=1.%20HSRP%20basichttp://en.wikipedia.org/wiki/Hexidecimalhttp://tools.ietf.org/html/rfc2281http://tools.ietf.org/html/rfc2281http://en.wikipedia.org/wiki/Default_gatewayhttp://en.wikipedia.org/wiki/Proprietary_protocolhttp://en.wikipedia.org/wiki/Cisco_Systems,_Inc.


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If priorities are different, a new router joining with a higher priority becomes

active, even if preemption is not configured; however, if the router is already up and its

priority changes (because of tracking or reconfiguration), it won't bump the primary

without preemption configured.

HSRP uses three types of multicast messages to exchange standby group

information:

HelloThe hello message contains the sending router's priority and stateinformation. Hellos are exchanged every three seconds. If a router fails to send a hello

in a specified amount of time, the receiving router, if priority dictates, becomes the

primary router for the group.

CoupWhen a secondary router becomes the primary router, it sends acoup message to the routers in the group.

ResignWhen the primary router is about to shut down, or when it hasreceived a hello message with a higher priority than its own, it forfeits the primary

position with a resign message.

Packet formats

The standby protocol run on top of UDP, and uses port number 1985. Packets are sent to

multicast address 224.0.0.2 with TTL 1.

Routers use their actual IP address as the source address for protocol packets, not the

virtual IP address. This is necessary so that the HSRP router can identify each other.

The format of the data portion of the UDP datagram is:

1 2 3

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4

6 7 8 9 0 1

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Version Op Code State HellotimeHoldtime Priority Group Reserved

Authentication DataAuthentication DataVirtual IP Address

States in HSRP:

An HSRP router can be in one of six states:

Initial Learn Listen Speak Standby Active

There are three types of timer is used in the HSRP protocol is active, standby, hello.

Without a hello packet received from a Active HSRP router in active time, the router

switch to a new HSRP state.

Active timer: used to monitor the Active Router. Timer will reset at any time when a

router in the HSRP group received hello packet is sent out from the Active Router. Timer

expire values in accordance with the hold time value is being set corresponding to the

field in HSRP hello messages.

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Standby timer: used to monitor the standby router. Timer will reset at any time when a

router in the HSRP group received hello packet is sent out from Standby Router. Timer

expire values in accordance with the hold time value is being set corresponding to the

field in HSRP hello messages.

Hello timer: hello packet time. All HSRP router in any state of HSRP are created out

hello packet that hello timer expire.

In the standby state, because the router at this time as a candidate to become the next

active router. It periodically sends hello packets. It also listen to the hello message from

the active router. In a HSRP network, only a standby router.

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In Active State, router can forward packets tasks. It sends virtual MAC address of group.

It is also tasked to respond to the ARP request packets directed to the virtual IP. Active

router also periodically send hello message. In an HSRP group has only one Active

Router.

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PART II: LAB

2.1 GOAL

All IP addresses have been preconfigured as following: NewYork: F0/0: 192.168.1.1 /24 NewYork: F1/0: 192.168.2.1 /24 NewJersey: F0/0: 192.168.1.2 /24 NewJersey F1/0: 192.168.2.2 /24 L.A.: F0/0: 192.168.1.3 /24 L.A.: F1/0: 192.168.2.3 /24 HOST: F0/0: 192.168.1.200 /24 ISP: F0/0: 192.168.2.254 /24

The ISP router has the following loopback interfaces, these are used to simulatethe Internet.

Loopback0: 172.16.1.1 /24 Loopback1: 172.16.2.1 /24 Loopback2: 172.16.3.1 /24

The host router has been configured with "no ip routing" which will turn it into anordinary host.

OSPF has been configured on all routers except the host router for fullconnectivity.

Configure NewYork, Newjersey and L.A. for HSRP, use the standby groupnumber "1".

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The virtual IP Address should be 192.168.1.254 /24 . The virtual mac addressshould be 1234.5678.9abc.

Newjersey should be the Active router, when it fails L.A. should take over. Hello packets should be sent every 7 seconds. Make sure the router with highest priority will always be the active router. Configure authentication for HSRP, use password "hutech". When the HSRP active router's F1/0 interface goes down, make sure it's no longer

the active HSRP router.

Configure the virtual IP address of HSRP as default gateway on the Host Router. Ensure you can ping the loopbacks of the ISP router from the Host router. Ensure that whenever 2 out of 3 routers are down, the Host router still has

connectivity to the ISP.

2.2 MODEL

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2.3 SOLUTION

NewJersey(config)#int f0/0

NewJersey(config-if)#standby 1 ip 192.168.1.254

NewJersey(config-if)#standby 1 mac-address 1234.5678.9abc

NewJersey(config-if)#standby 1 priority 200( priority value from 0 -> 255)

NewJersey(config-if)#standby 1 timers 7 21( value to 1 -> 254)

NewJersey(config-if)#standby 1 preempt

NewJersey(config-if)#standby 1 authentication hutech

NewJersey(config-if)#standby 1 track 1 decrement 11(decrement value from 1-255,

tracked object value from 1-500)

NewJersey(config)#track 1 interface fastEthernet 1/0 line-protocol

NewYork(config)#int f0/0

NewYork(config-if)#standby 1 ip 192.168.1.254

NewYork(config-if)#standby 1 mac-address 1234.5678.9abc

NewYork(config-if)#standby 1 priority 180

NewYork(config-if)#standby 1 timers 7 21

NewYork(config-if)# standby 1 preempt

NewYork(config-if)#standby 1 authentication hutech

LA(config)#int f0/0

LA(config-if)#standby 1 ip 192.168.1.254

LA(config-if)#standby 1 mac-address 1234.5678.9abc

LA(config-if)#standby 1 priority 190

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LA(config-if)#standby 1 timers 7 21

LA(config-if)#standby 1 preempt

LA(config-if)#standby 1 authentication hutech

LA(config)#track 1 interface fastEthernet 1/0 line-protocol

Host(config)#no ip routing

Host(config)ip default-gateway 192.168.1.254

After shutdown interface f1/0 on router LA:

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Turn on interface f1/0 on router LA thenshutdown interface f1/0 on router NewJersey

Ping Host to ISP:

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After turn of any two routers

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Wireshark capture:

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