HSRP: RUNNING ON TWO ROUTERS – SCENARIO 3


TOPIC

HSRP SCENARIO

CONFIGURATION

HOW HSRP WORKS

CONCLUSION POINTS


 

HSRP SCENARIO

We have two routers with rtr1 & rtr2, with physical interfaces & sub-interfaces.

Gi0/1 is the physical interface.

Gi0/2.2, Gi0/2.3 & Gi0/2.132 are sub-interfaces.

4 different VLAN’s or subnets are assigned to 4 different interfaces (Gi0/1, Gi0/2.2, Gi0/2.3, and Gi0/2.132.

We need to make rtr1 as primary for all the interfaces & rtr2 as secondary.

 ***********************

 

CONFIGURATION

rtr1#sh standby br

Interface   Grp Pri P State   Active         Standby         Virtual IP

Gi0/1       1   105 P Active local           10.156.26.195   10.156.26.193

Gi0/2.2     1   105 P Active local         10.156.26.3     10.156.26.1

Gi0/2.3     1   105 P Active local           10.156.0.3     10.156.0.1

Gi0/2.132   2   105 P Active local           10.156.26.131   10.156.26.129

 

rtr2#sh standby br

Interface   Grp Pri P State   Active         Standby         Virtual IP

Gi0/1       1   100 P Standby 10.156.26.194   local           10.156.26.193

Gi0/2.2     1   100 P Standby 10.156.26.2     local           10.156.26.1

Gi0/2.3     1   100 P Standby 10.156.0.2     local           10.156.0.1

Gi0/2.132   2   100 P Standby 10.156.26.130   local           10.156.26.129


 

HOW HSRP WORKS?

Suppose, host with ip 10.156.26.197 sends traffic towards edge devices, rt1 & rtr2.

This host ip belongs to the same subnet, which related to interface Gi0/1.

First of all, request from host will go to the virtual ip or HSRP group ip, assigned to this subnet, i.e, 10.156.26.193.

Now, request can go to either of rtr1 & rtr2.

But, here, comparison will be done between rtr1 & rtr2 based on HSRP priority.

rtr1 wins the comparison, as rtr1 is acting as primary.

Finally, Request from host will go to rtr1.

******************

 

CONCLUSION

On both the devices, corresponding interfaces to each other are compared.

Example, Gi0/1 on device (3945) is compared with device (rtr2).

 

We can use single HSRP or Standby group for number of interfaces (or vlan’s or subnets).

Example: we have used HSRP group 1 for interfaces Gi0/1, Gi0/2.2 & Gi0/2.3

Note: we are using single HSRP group for number of interfaces, but with different virtual ip’s.

Note: we can use single HSRP group for number of physical interfaces & sub-interfaces both.

 

Here, if we want, we can achieve the HSRP redundancy using single HSRP group for all the interfaces.

Theoretically, Single HSRP group can be used for as many interfaces (or vlan’s or subnets), as you want.

Practically, there is some limitation; it is a standard practice to use more than one HSRP group, if we want to achieve load sharing for more than 7 or 8   interfaces (or vlans or subnets), otherwise router processor utilization will be very high.


Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s