My CISCO Journal

VRRP: Virtual Router Redundancy protocol

To reach remote networks we use the following methods to discover the first hop to our remote network:

The problem with dynamic exploration is extra network overhead, and usually static configuration is recommended as it gives the next hop detail in advance thus reducing the extra network overhead. But the problem with static next hop or in simple words default gateway configuration is redundancy as it creates a single point of failure. To overcome this, we use different redundancy configuration techniques, in which we configure a single virtual IP on a group of routers. In case one virtual gateway fails, the load is instantly shifted to the next available router according to priority. VRRP is one of those techniques as are GLBP and HSRP. In VRRP we define a Master Router and a bunch of back up routers; these backup routers are the point of redundancy in case of Master router failure. 

For example in above scenario, we have configured VRRP on all the three routers and made it a part of VRRP group 1. The mentioned virtual IP address is configured on each router. Suppose if Router A is currently active and some things abnormal happens to it, Router B or Router C will take the backup gateway place according to the priority defined for these routers in VRRP group configurations. In the same fashion we can also create different groups, with different priorities and VRRP advertisements timer values.

Quick Facts about VRRP:

We will use GNS3 to implement GLBP. We are using two hosts with same default gateway. Our configuration check list is:

We are using R1 and R2 to simulate our hosts in GNS3. The configuration on both these routers is:

R1(HostA)

R1#show running-config interface fastEthernet 0/0

Building configuration...

Current configuration : 96 bytes

!

interface FastEthernet0/0

 ip address 192.168.1.1 255.255.255.0

 duplex auto

 speed auto

end

and a static route is define to point it to our default-gateway: 192.168.1.10

R1#show ip route static

S*   0.0.0.0/0 [1/0] via 192.168.1.10

Same sort of configuration is done on R2(HostB) too:

R2#show running-config interface fastEthernet 0/0

Building configuration...

Current configuration : 96 bytes

!

interface FastEthernet0/0

 ip address 192.168.1.2 255.255.255.0

 duplex auto

 speed auto

end

R2#show ip route static

S*   0.0.0.0/0 [1/0] via 192.168.1.10

R3 and R4 are our Gateways on which we will load balance the traffic and create redundancy using GLBP. Please note EIGRP is configured as routing protocol with AS # 4 on R3-R4-R5. In the next step we will enable GLBP on Fast Ethernet 0/0 interface of R3 and R4. The configuration done on each router interface is as follow:

R3#show running-config interface fastEthernet 0/0

Building configuration...

Current configuration : 283 bytes

!

interface FastEthernet0/0

 mac-address 0033.3333.3333

 ip address 192.168.1.3 255.255.255.0

 duplex auto

 speed auto

 glbp 4 ip 192.168.1.10

 glbp 4 priority 120

 glbp 4 preempt

 glbp 4 weighting 6

 glbp 4 load-balancing weighted

 glbp 4 authentication md5 key-string shah123

end

The routing configuration on R3 is as follow:

R3#show ip route eigrp

D    10.0.0.0/8 [90/409600] via 192.168.3.5, 00:09:27, FastEthernet0/1

D    192.168.2.0/24 [90/307200] via 192.168.3.5, 00:09:27, FastEthernet0/1

                    [90/307200] via 192.168.1.4, 00:09:27, FastEthernet0/0

R3#show ip route

Output ommited

Gateway of last resort is not set

D    10.0.0.0/8 [90/409600] via 192.168.3.5, 00:09:35, FastEthernet0/1

C    192.168.1.0/24 is directly connected, FastEthernet0/0

D    192.168.2.0/24 [90/307200] via 192.168.3.5, 00:09:35, FastEthernet0/1

                    [90/307200] via 192.168.1.4, 00:09:35, FastEthernet0/0

C    192.168.3.0/24 is directly connected, FastEthernet0/1

As you can see GLBP group number 4 is configured on R3 with virtual gateway IP : 192.168.1.10. The priority is set to 120, as we want to make this router AVG ( Active Virtual Gateway), authentication and load balancing also adjusted. We can create various type of load balancing but here we are using weighting. The configurations on R4 are almost same, but we have given a little bit low priority number to this gateway as we would like to make it GLBP Virtual Forwarder. The configurations are as follow:

R4#show running-config interface fastEthernet 0/0

Building configuration...

Current configuration : 283 bytes

!

interface FastEthernet0/0

 mac-address 0044.4444.4444

 ip address 192.168.1.4 255.255.255.0

 duplex auto

 speed auto

 glbp 4 ip 192.168.1.10

 glbp 4 priority 110

 glbp 4 preempt

 glbp 4 weighting 7

 glbp 4 load-balancing weighted

 glbp 4 authentication md5 key-string shah123

end

R4#show ip route eigrp

D    10.0.0.0/8 [90/409600] via 192.168.2.5, 00:16:45, FastEthernet0/1

D    192.168.3.0/24 [90/307200] via 192.168.2.5, 00:16:45, FastEthernet0/1

                    [90/307200] via 192.168.1.3, 00:16:45, FastEthernet0/0

R4#show ip route

Output omitted.

Gateway of last resort is not set

D    10.0.0.0/8 [90/409600] via 192.168.2.5, 00:17:10, FastEthernet0/1

C    192.168.1.0/24 is directly connected, FastEthernet0/0

C    192.168.2.0/24 is directly connected, FastEthernet0/1

D    192.168.3.0/24 [90/307200] via 192.168.2.5, 00:17:10, FastEthernet0/1

                    [90/307200] via 192.168.1.3, 00:17:10, FastEthernet0/0

The configuration on our last router, R5, on which we will create a loop back 5 interface to test ping it from R1 and R2 to check our GLBP load balancing and redundancy, is:

R5#show ip route

Gateway of last resort is not set

     10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

C       10.0.0.0/24 is directly connected, Loopback5

D       10.0.0.0/8 is a summary, 00:31:59, Null0

D    192.168.1.0/24 [90/307200] via 192.168.3.3, 00:19:12, FastEthernet0/0

                    [90/307200] via 192.168.2.4, 00:19:12, FastEthernet0/1

C    192.168.2.0/24 is directly connected, FastEthernet0/1

C    192.168.3.0/24 is directly connected, FastEthernet0/0

And we are done! Now we are good to go, we can check the GLBP and verify it via the following commands:

R4#show glbp

FastEthernet0/0 - Group 4

  State is Standby

    3 state changes, last state change 00:20:20

  Virtual IP address is 192.168.1.10

  Hello time 3 sec, hold time 10 sec

    Next hello sent in 0.904 secs

  Redirect time 600 sec, forwarder time-out 14400 sec

  Authentication MD5, key-string "shah123"

  Preemption enabled, min delay 0 sec

  Active is 192.168.1.3, priority 120 (expires in 8.472 sec)

  Standby is local

  Priority 110 (configured)

  Weighting 7 (configured 7), thresholds: lower 1, upper 7

  Load balancing: weighted

  Group members:

    0033.3333.3333 (192.168.1.3) authenticated

    0044.4444.4444 (192.168.1.4) local

  There are 2 forwarders (1 active)

  Forwarder 1  ---------------  >Active virtual Gatway

    State is Listen

    MAC address is 0007.b400.0401 (learnt)

    Owner ID is 0033.3333.3333

    Time to live: 14398.476 sec (maximum 14400 sec)

    Preemption enabled, min delay 30 sec

    Active is 192.168.1.3 (primary), weighting 6 (expires in 9.976 sec)

  Forwarder 2 ----------------- > GLBP virtual Forwarder

    State is Active

      3 state changes, last state change 00:20:03

    MAC address is 0007.b400.0402 (default)

    Owner ID is 0044.4444.4444

    Preemption enabled, min delay 30 sec

    Active is local, weighting 7

And the output of the same command on R3 is as:

R3#show glbp

FastEthernet0/0 - Group 4

  State is Active

    2 state changes, last state change 00:30:01

  Virtual IP address is 192.168.1.10

  Hello time 3 sec, hold time 10 sec

    Next hello sent in 1.568 secs

  Redirect time 600 sec, forwarder time-out 14400 sec

  Authentication MD5, key-string "shah123"

  Preemption enabled, min delay 0 sec

  Active is local

  Standby is 192.168.1.4, priority 110 (expires in 8.052 sec)

  Priority 120 (configured)

  Weighting 6 (configured 6), thresholds: lower 1, upper 6

  Load balancing: weighted

  Group members:

    0033.3333.3333 (192.168.1.3) local

    0044.4444.4444 (192.168.1.4) authenticated

  There are 2 forwarders (1 active)

  Forwarder 1

    State is Active

      1 state change, last state change 00:29:51

    MAC address is 0007.b400.0401 (default)

    Owner ID is 0033.3333.3333

    Redirection enabled

    Preemption enabled, min delay 30 sec

    Active is local, weighting 6

    Arp replies sent: 1

  Forwarder 2

    State is Listen

      2 state changes, last state change 00:24:42

    MAC address is 0007.b400.0402 (learnt)

    Owner ID is 0044.4444.4444

    Redirection enabled, 599.216 sec remaining (maximum 600 sec)

    Time to live: 14399.212 sec (maximum 14400 sec)

    Preemption enabled, min delay 30 sec

    Active is 192.168.1.4 (primary), weighting 7 (expires in 9.208 sec)

    Arp replies sent: 2

to see our GLBP in action, we issue a ping from Host A ( R1) to 10.0.0.4 loopback interface on R5, arp debugging has been enabled on Host A to check GLBP in action. Here is the output:

R1#ping 10.0.0.4

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 10.0.0.4, timeout is 2 seconds:

*Mar  1 00:47:57.511: IP ARP: creating incomplete entry for IP address: 192.168.1.10 interface FastEthernet0/0

*Mar  1 00:47:57.515: IP ARP: sent req src 192.168.1.1 c001.17a4.0000,

                 dst 192.168.1.10 0000.0000.0000 FastEthernet0/0

*Mar  1 00:47:57.547: IP ARP: rcvd rep src 192.168.1.10 0007.b400.0402, dst 192.168.1.1 FastEthernet0/0.

*Mar  1 00:47:59.591: IP ARP: rcvd req src 192.168.1.4 0044.4444.4444, dst 192.168.1.1 FastEthernet0/0

*Mar  1 00:47:59.595: IP ARP: creating entry for IP address: 192.168.1.4, hw: 0044.4444.4444

*Mar  1 00:47:59.599: IP ARP: sent rep src 192.168.1.1 c001.17a4.0000,

                 dst 192.168.1.4 0044.4444.4444 FastEthernet0/0.!!!

Success rate is 60 percent (3/5), round-trip min/avg/max = 28/42/56 ms

R1#show ip arp

Protocol  Address          Age (min)  Hardware Addr   Type   Interface

Internet  192.168.1.10           36   0007.b400.0402  ARPA   FastEthernet0/0

R1#traceroute 10.0.0.4

Type escape sequence to abort.

Tracing the route to 10.0.0.4

  1 192.168.1.4 28 msec 36 msec 20 msec ---- > R4 Fast Ethernet 0/0 interface for outgoing packet

  2 192.168.2.5 40 msec *  40 msec

That is great! Our new gateway has been resolved by host A while communicating with R5 loopback interface (10.0.0.4). Okay we have confirmed that our GLBP is working great virtual MAC and IP assignment is working perfectly. Now if we want to check whether redundancy is working or not, we can do the following, we will disable the Fast Ethernet 0/0 interface on R4, and check if R3 is taking its place or not:

R1#ping 10.0.0.4 repeat 2000

Type escape sequence to abort.

Sending 2000, 100-byte ICMP Echos to 10.0.0.4, timeout is 2 seconds:

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!.....!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!.

Success rate is 99 percent (730/736), round-trip min/avg/max = 8/34/112

During the above highlighted instance Interface Fast Ethernet 0/0 was shut down on R4 and the traffic was shifted after a minor glitch to R3, as can be seen from below output:

R1#show ip arp

Protocol  Address          Age (min)  Hardware Addr   Type   Interface

Internet  192.168.1.10            0   0007.b400.0401  ARPA   FastEthernet0/0

Internet  192.168.1.1             -   c001.17a4.0000  ARPA   FastEthernet0/0

Internet  192.168.1.3             0   0033.3333.3333  ARPA   FastEthernet0/0

As you can the virtual MAC address corresponding to Virtual GW (192.168.1.10) changed from 0007.b400.0402 ---- > 0007.b400.0401!! isn’t it great J

In short GLBP is a very good redundancy and load balancing protocol. AVG is responsible for keeping any eye on all Virtual forwarders and assigning virtual MACs according to network requirements. Active Virtual Gateway redundancy is managed by GLBP priority value and Active virtual forwarders are controlled via weight value in the configurations.