Web Hosting by Netfirms | Free Domain Names by Netfirms

• HSRP: Hot Standby Router Protocol
• Virtual Router Redundancy Protocol (VRRP)
• Gateway Load Balancing Protocol (GLBP)

HSRP: Hot Standby Router Protocol

• Runs on Multicast IP 224.0.0.2  utilizing UDP port 1985
• Creates a third or common MAC Address and Shares the IP, only one is active at a time.
• Keyword STANDBY
• Some troubles can be corrected by using the "standby use-bia" command.
• RFC 2281
• With frame relay circuits: track SUB-Interface to ensure rollover.
• MAC address 0000.0c07.ac0e = HSRP ARP for Vlan14 (0e)
   
• VRRP : Virtual Router Redundancy Protocol - standards based solution.

HSRP works by the exchange of multicast (224.) messages that advertise priority among HSRP configured routers. When the active router fails to send a hello message within a configurable period of time, the standby router with the highest priority becomes the active router. The transition of packet forwarding functions between routers is completely transparent to all hosts on the network.

HSRP configured routers exchange three types of multicast messages:
Hello - The hello message conveys to other HSRP routers the routers HSRP priority and state information. By default, an HSRP router sends hello messages every three seconds.
Coup - When a standby router assumes the function of the active router, it sends a coup message.
Resign - A router that is the active router sends this message when it is about to shut down or when a router that has a higher priority sends a hello message.

At any one time, HSRP configured routers are in one of the following states:
Active - The router is performing packet transfer functions.
Standby - The router is prepared to assume packet transfer functions if the active router fails.
Speaking and listening - The router is sending and receiving hello messages.
Listening - The router is receiving hello messages.

ICMP redirects are DISABLED by default when you're running HSRP, because hosts would end up with the real MAC Address.

HSRP uses a third (Common)  IP address  and a special MAC address on the cable. So when everything is up, A is actually listening for two addresses - both its normal address and the HSRP address. If router A goes down, router B only grabs the HSRP address. The highest priority router in an HSRP group is the winner of the MAC address.

The random / common  MAC address is a based on the HSRP GROUP NUMBER assigned to the interface.

Configuration Examples

• Configure on interfaces, Prompt STANDBY
• Default priority is 100, subtract 10 for loss of tracked interfaces.
• Track SUB interfaces in Frame networks to avoid one sided issues.
• Must have "PREEMPT" to force switch of HSRP interfaces.
• Make Sure timers are in Synch.
• May have more than ONE group per interface.
• If all routers have same Priority - the one with the HIGHEST configured IP takes over.

router 1 - Configured to be ACTIVE and Tracking HSSI interface 0/0.1 with password.
!
interface FastEthernet1/0/0
 description POLNET            > Change address to 240
 ip address 204.178.220.202 255.255.255.0
 no ip redirects
 no ip directed-broadcast
 full-duplex
 no mop enabled
 standby 10 timers 5 10
 standby 10 priority 108
 standby 10 preempt
 standby 10 authentication P0LPASSWORD
 standby 10 ip 204.178.220.240
 standby 10 track Hssi0/0.1

 standby 10 preempt delay minimum 120
!
router 2 - Configured to be Standby and Tracking HSSI interface 0/0.1 with password.
!
interface FastEthernet1/0 description POLNET            > Change address to 240
 ip address 204.178.220.203 255.255.255.0
 no ip redirects
 no ip directed-broadcast
 full-duplex
 standby 10 timers 5 10
 standby 10 preempt
 standby 10 authentication P0LPASSWORD
 standby 10 ip 204.178.220.240
 standby 10 track Hssi0/0.1

standby 10 preempt delay minimum 120

Commands

POL-7507-1#sho stand fa 1/0/0 FastEthernet1/0/0 - Group 10   Local state is Active, priority 108, may preempt   Hellotime 5 holdtime 10 configured hellotime 5 sec holdtime 10 sec   Next hello sent in 00:00:01.192   Hot standby IP address is 204.178.220.240 configured   Active router is local   Standby router is 204.178.220.203 expires in 00:00:05   Tracking interface states for 1 interface, 1 up:     Up   Hssi0/0.1

POL-7507-2#sho stand fa 1/0 FastEthernet1/0 - Group 10   Local state is Standby, priority 100, may preempt   Hellotime 5 holdtime 10 configured hellotime 5 sec holdtime 10 sec   Next hello sent in 00:00:04.084   Hot standby IP address is 204.178.220.240 configured   Active router is 204.178.220.202 expires in 00:00:09   Standby router is local   Tracking interface states for 1 interface, 1 up:     Up   Hssi0/0.1

 

POL-7507-1#sho stand bri                      P indicates configured to preempt.                      | Interface   Grp Prio P State    Active addr     Standby addr    Group addr Fa1/0/0     10  108  P Active   local           204.178.220.203 204.178.220.240 Et4/0/0     20  108  P Active   local           205.229.193.3   205.229.193.1 Et4/0/1     30  108  P Active   local           204.178.221.6   204.178.221.1 Et4/0/2     40  108  P Active   local           208.193.93.250  208.193.93.249 Et4/0/3     70  108  P Active   local           208.193.92.3    208.193.92.1 Et4/0/4     50  108  P Active   local           198.242.44.203  198.242.44.240 Et4/0/5     80  108  P Active   local           208.225.164.3   208.225.164.1 Et4/0/7     60  108  P Active   local           unknown         192.168.1.1

POL-7507-2#sho stand bri                     P indicates configured to preempt.                      | Interface   Grp Prio P State    Active addr     Standby addr    Group addr Fa1/0       10  100  P Standby  204.178.220.202 local           204.178.220.240 Et4/0       20  100  P Standby  205.229.193.2   local           205.229.193.1 Et4/1       30  100  P Standby  204.178.221.2   local           204.178.221.1 Et4/2       40  100  P Standby  208.193.93.251  local           208.193.93.249 Et4/3       70  100  P Standby  208.193.92.2    local           208.193.92.1 Et4/4       50  100  P Standby  198.242.44.202  local           198.242.44.240 Et4/5       80  100  P Standby  208.225.164.2   local           208.225.164.1 POL-7507-2#

Multigroup HSRP (MHSRP) is an extension of HSRP that allows a single router interface to belong to more than one Hot Standby group.
You can design a environment to have different routers take traffic (offload) and have fallbacks kick in if needed.
This works because the MAC address created revolves around the standby group.
 

Example

hostname RouterA	hostname RouterB
interface ethernet 0 !Priority ON ip address 1.0.0.1 255.0.0.0 standby 1 ip 1.0.0.3 standby 1 priority 110 standby 1 preempt !Standby standby 2 ip 1.0.0.4 standby 2 preempt	interface ethernet 0 ip address 1.0.0.2 255.0.0.0 !Standby standby 1 ip 1.0.0.3 standby 1 preempt !Priority ON standby 2 ip 1.0.0.4 standby 2 priority 110 standby 2 preempt

hostname RouterB
!
interface ethernet 0
ip address 1.0.0.2 255.0 0.0
standby 1 ip 1.0.0.5
standby 1 priority 110
standby 1 preempt
standby 1 authentication sclara
standby 2 ip 1.0.0.6
standby 2 priority 110
standby 2 preempt
standby 2 authentication mtview
standby 3 ip 1.0.0.7
standby 3 preempt
standby 3 authentication svale
!
 

Data flows on MULTICAST DLC and IP Address using port 1985

DLC:  ----- DLC Header -----
DLC:
DLC:  Frame 23 arrived at  12:34:21.7570; frame size is 62 (003E hex) bytes.
DLC:  Destination = Multicast 01005E000002
DLC:  Source      = Station Cisco 07AC0A
DLC:  Ethertype   = 0800 (IP)
DLC:
IP: ----- IP Header -----
IP:
IP: Version = 4, header length = 20 bytes
IP: Type of service = 00
IP:       000. .... = routine
IP:       ...0 .... = normal delay
IP:       .... 0... = normal throughput
IP:       .... .0.. = normal reliability
IP: Total length    = 48 bytes
IP: Identification  = 0
IP: Flags           = 0X
IP:       .0.. .... = may fragment
IP:       ..0. .... = last fragment
IP: Fragment offset = 0 bytes
IP: Time to live    = 2 seconds/hops
IP: Protocol        = 17 (UDP)
IP: Header checksum = 2F3E (correct)
IP: Source address      = [204.178.220.202]
IP: Destination address = [224.0.0.2]
IP: No options
IP:
UDP: ----- UDP Header -----
UDP:
UDP: Source port      = 1985 (Cisco HSRP)
UDP: Destination port = 1985 (Cisco HSRP)
UDP: Length           = 28
UDP: Checksum         = D8CC (correct)
UDP: [20 byte(s) of data]
UDP:
HSRP:
HSRP: Version                = 0
HSRP: Opcode                 = 0 (Hello)
HSRP: Sending router's state = 16 (Active)
HSRP: Hello time             = 5
HSRP: Hold time              = 10
HSRP: Router's priority      = 108
HSRP: Group number           = 10
HSRP: Reserved
HSRP: Authentication         = "P0LPASSWORD"
HSRP: IP address             = 204.178.220.240
 

Virtual Router Redundancy Protocol (VRRP)

• IEEE Standard RFC 2338
• Master Router takes traffic
• Lan and MPLS interfaces
• Highest Priority is Master 1-254 : default is 100
• Hellos sent by Master on 224.0.0.18 every one second
• Times can be changed "timers advertise X"

Gateway Load Balancing Protocol (GLBP)

• Hellos sent on 224.0.0.102 every 3 seconds
• AVG - Active Virtual Gateway - Responds to ARPs on Group, hands out the AVF MACs to clients
• AVF - Active Virtual Forwarder - assigned by the AVG
• Highest Priority is Active :  1-254 : default is 100
• Distribution by (Round Robin, Weighted and Host)