hsrp / glbp

[hs08]

Hello,

If we have simple topology like this picture where Core 1 and Core 2 run HSRP/GLBP, i just want to know if connection from C1 to C2 is mandotary needed or we can remove that?

[M02@rt37]

Hello @hs08,

As concerned HSRP/GLBP you want to configure between the two core, it is not mandatory to have this link.

[hs08]

Hello,

I read many reference if we using HSRP / GLBP we will facing with STP issue, i believe with that topology we will facing this issue, am i right?

If we remove the connection from C1 and C2 and add another DS so the topology will be like below picture, we will not facing any issue with STP and HSRP / GLBP can running normally, am i right?

[M02@rt37]

@hs08,

If you have redundant connections between switches, STP will come into play to determine which links should be active and which ones should be in a blocking state. This can cause certain links to be blocked, which might affect the efficiency of HSRP or GLBP.

But in this scenario, without a direct link between the two core switches, you can potentially avoid STP-related issues such as loops. By using HSRP or GLBP, you can achieve redundancy and load balancing between the core switches without the need for STP to block any links.

With HSRP or GLBP, one distribution switch (DS1 or DS2) can be the active router for certain VLANs on Core 1, while the other distribution switch serves as the active router for the same VLANs on Core 2. This allows for active-active links and avoids the need for STP to block any connections.

It's essential to ensure that your HSRP or GLBP configurations are properly set up to achieve the desired redundancy and load balancing.

[paul driver]

Hello
The direct connection between CS1-CS2 is NOT required, the premise of FHRP is to provide redundancy from a shared physical segment, in as such CS1-2/DS1 will share the same lan subnets with multiple FHRP groups , the FHRP hellos from either router will be seen across this segment, which is totally transparent to the hosts (DS1) providing the active/primary and standby roles.

[Flavio Miranda]

Hi

 Although the connection is not mandatory for hsrp , I never saw one topology where the core 1 would not be connect to Core 2 physically. 

 If you are worried about STP, put both cores in stack or vss, this way you keep physical redundancy and have one logical device. Or use layer3 between Core and access. 

 The problem with not connecting cores would be with upwards connection to routers and internet link.

[Richard Burts]

I am puzzled by the responses that a connection c1 to c2 is not required. If there is not a connection c1 to c2 how will the negotiation for active/standby take place?

[Flavio Miranda]

You are right Sir. My mistake. Althouth we can set the priority on the access switch side, the cores need to negociate who will respond on the VIP.

 Meaning, make no sense a topology without physical connection between cores.

[hs08]

Hello @Flavio Miranda 

So the connection from Core 1 and Core 2 is mandotary, right? The connection across the cores should be L2 or L3?

[Flavio Miranda]

it is.  You must use L2 connection.

 Configure an interface vlan on Core 1 and the same for Core 2.  Use a port-channel with, at least, two interfaces  between Cores for better redundancy.

[hs08]

Hi @Flavio Miranda 

Thanks, so we must aware about STP with triangle topology, am i right?

[MHM Cisco World]

check below

[Flavio Miranda]

Yeah, when you connect the two cores and you connect the access switch to both cores, the STP will disable one uplink on the access switch, that´s the down side of using Layer2 between Access and Cores and have separated Cores and not stack or VSS.

 But this is by far the most used scenario.

I had the opportunity of create a topology where I used Layer3 between Access and Core but if you need to extend a vlan from one place to another you have a problem.

[paul driver]

Hello

---

@Flavio Miranda wrote:

it is.  You must use L2 connection.

---

I have to disagree - it is NOT mandatory 

[paul driver]

Hello @Richard Burts @Flavio Miranda 
For CS1-CS2 to negotiate active/standby roles they will use the shared physical connection into DS1, this will be L2/L3 and if either link to DS1 fails that CSx device will then be isolated as such the FHRP will transition to active/active on both CS1/2 however only one CSx will be still valid and active FHRP vips, the one with the active physical connection