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Loosing packets when running HSRP?


I have a network with 2 sites. On each site I have a stack ofh 3750:s. Between the sites there is a Layer2-connection from a provider. They deliver a 1Gbps l2-connection with ethernet-interfaces, so it works simply as one long patch-cable.

In the 3750:s there are 20 vlans created, and the l2-connection ports are simple trunks with no vlan filtering. The same vlans exists on both sites.

About 10 vlans are routed by the 3750 on site A. Each vlan-interface is configured for hsrp on both sites, where the 3750 on site A has higher priority in all vlan:s. So, all routing occurs at site A. And here's why:

If I create a new unused vlan on both sites and connect one host per site to the vlan (switchport access vlan x) i get a completely good working connection between them. When I create a L3-interface for the vlan on the switch in site B I can ping the router interface IP. However, when I configure the vlan interface for hsrp (only on site B at this moment) I can from the host on site A ping the IP-address dedicated to the vlan interface (int vlanx, ip address x.x.x.x) BUT when I ping the standby IP (int vlanx, standby ip x.x.x.y) i loose about 80% of the packets.


Site A


Host with IP .10 connected to 3750 switchport configured as "switchport vlan 400, switchport mode access".

A trunk connected to a switchport, going to site B. "switchport mode trunk"

Site B:


Host .3 connected to switchport configured as "switchport mode access, switchport access vlan 400"

A trunk connected to a switchport, going to site B. "switchport mode trunk"

3750 configured as

interface vlan 400

ip address .254

standby ip .1

standby priority ....

Now, on Site A:

.10 can ping .254 ok

.10 can ping .3 ok

.10 when pinging .1 gets 80% packet loss.

.3 can ping .1 ok

.3 can ping .254 ok

.3 can ping .10 ok

Also, when doing the opposite; creating the vlan400-interface ONLY on site A 3750 and trying to ping both IP:s from site B i am not getting any packet-loss. So it has something to do with running HSRP on the site B switch.

Any input? The switches are not running the exact same OS version, but they will do soon to eliminate this source of error.

Thanks in advance!

regards Jimmy


Re: Loosing packets when running HSRP?

The priority of the device can change dynamically if an interface is configured with the "standby track" command and another interface on the router goes down.

The following URL may help to get more information:

Community Member

Re: Loosing packets when running HSRP?

Yes of course. But in what sense does it apply to my case?




Re: Loosing packets when running HSRP?

Maybe you can explain your setup a little more , don't understand why you have hsrp if you have a single link between the sites ?

Community Member

Re: Loosing packets when running HSRP?


I have HSRP since I want routing to be with redundancy. The connection between the site is a L2 trunk. There is also WAN-connections that the ISP will deliver with HSRP to both sites.

Look at this as if there is only one site with a TP-cable-trunk between the 3750:s. Only that the 3750:s are separated with a looooong cable. ;-)

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