HSRP topology issue

shibindong · ‎07-17-2008

Please take a look at the attached topology, if there is a switch put between R1, R2 and R3, R4, logically they are full mesh, so we can address the IP as indicating in the topology, my questions is: if we have to go for direct connection without switch (no full mesh), can we still address the same IP on the routers and expected HSRP still work?

shibindong · ‎07-17-2008

please find attached topology

milan.kulik · ‎07-18-2008

Hi,

HSRP works as far as there is a L2 connection between routers configured for the same HSRP group.

I.e., even if routers connected directly via a cross Ethernet cable.

The question is:

Who would use the virtual IP address then (no one able to connect to the same segment)?

BR,

Milan

Joseph W. Doherty · ‎07-18-2008

Perhaps there's some confusion about subnets, full mesh, HSRP, etc.?

Normally, a full mesh would be each of your routers has a connection to all the other routers on individual routed links. Each of these links are usually configured point-to-point with different network addresses, often /30, for each. (Would be six links for your four router.)

With a switch (or hub), each router would have only one link to the same segment. Usually the segment would be just one subnet, often /24, and each router has an individual IP address within the segment.

HSRP provides a virtual gateway address for host usage on the same segment. For example, all four of your routers might support just one virtual IP address, such as an IP address of .1 and again with the routers having different physical addresses (often from the top or bottom of the address block, i.e. .2 .3 or .254 .253, etc.)