HSRP - only inbound reroute to standby router

[NoobGuy]

Hi,

I have configure HSRP to both my router(please refer to attachment for config).

 Scenario:

15:32:46: %HSRP-5-STATECHANGE: GigabitEthernet0/0/3 Grp 1 state Active -> Speak
15:32:56: %HSRP-5-STATECHANGE: GigabitEthernet0/0/3 Grp 1 state Speak -> Standby

Router 1(primary/Active) status change to standby and router

15:32:46: %STANDBY-6-STATECHANGE: GigabitEthernet2/2 Group 1 state Standby -> Active

Router 2 (secondary/standby) status change to active.

Issue: 

-In monitoring tools, only the inbound traffic going to Router 2 and the outbound traffic still going through Router 1.

I only realized this after the Router 1 change back to Active state.

Why this issue happen?.

Regards,

NoobGuy

[Jon Marshall]

Not clear what you mean by inbound and outbound ? 

Traffic will be sent to the active HSRP router but return traffic may not be. 

Perhaps you can clarify with a quick diagram ? 

Jon

[NoobGuy]

Hi Jon,

My monitoring monitor both the inbound and outbound, but only the inbound traffic swing to router to when router 1 status change to standby.

I already attached the graph and simple diagram.

Regards,

NoobGuy

[cmarva]

if I understand your scenario:

router 1 - hsrp standby

router 2 - hsrp primary

now, i don't know anything else about the way your network is set up, but that doesn't matter. All traffic from hosts on this vlan will go through router 2 to get to the rest of the network.

Traffic coming back from the network to hosts on this vlan can go through either router. If traffic comes from the backbone and gets to router 2, it has to forward the traffic to the host because the IP subnet is still a directly connected network, regardless of hsrp state.

when router 1 is primary, all hosts on that vlan will go through router 1 to get to the rest of the network. Any traffic coming back to the hosts from the network can go through either router. router 2 can forward the traffic to the hosts because that subnet is still a directly connected network.

the general rule here is hsrp is a first hop protocol, thus the hosts can only get off net via the hsrp primary. For destination based, whichever router has that subnet as a directly connected network can forward traffic back to the hosts.

[NoobGuy]

Hi cmarva,

Config:
Router 1: Primary/Active
Router 2: Secondary/Standby

During the incident:

Router 1: status change to standby

Router 2: status change to active

During the incident, the inbound traffic go through router 2 and outbound traffic go through router 1 from my monitoring. I already include monitoring screenshot in attachment.

so the traffic can still go to router 1 even status change to standby?

Regards,

NoobGuy

[Georg Pauwen]

Hello,

what is connected to both of these routers, what are they uplinked to ?

[Richard Burts · Accepted solution]

There is much that we do not know about your situation and that makes it difficult to give really good advice. Your diagram shows only a switch attached to 2 routers. It has no information about what is beyond the router or about how traffic from beyond the routers gets to them. And we have no information about caused the HSRP change from active to standby. So we can deal only in generalities at this point. 

My first generality is that HSRP is designed to influence how traffic from the Lan gets to the router. If there is an HSRP event and the active router transitions to standby and the standby transitions to active then it is the expected behavior that inbound traffic would shift. And I believe that is happening in your situation.

My second generality is that HSRP has no role to play in how traffic from the router gets to devices on the Lan. That is mostly determined by the routing policy that you have established. It is logical for us to assume that your routing policy was probably set up so that traffic from beyond the router pair would be sent to the router that is normally the active router. In that case when there is an HSRP event and the routers change which one is active there is probably not anything that changes the routing policy to match this. And so it is the expected behavior that outbound traffic would not switch to the other router based on an HSRP change.

HTH

Rick

[NoobGuy]

Hi Richard Burts,

Thank for explanation. I think my case fall into second generality. The LAN side influence by HSRP and the WAN side influence by OSPF cost.

Regards,
NoobGuy

[Richard Burts]

I am glad that our responses have been helpful. Thank you for marking this question as solved. This will help other participants in the community to identify discussions which have helpful information. This community is an excellent place to ask questions and to learn about networking. I hope to see you continue to be active in the community.

HTH

Rick