Routing problems: L3 + EIGRP stub + HSRP

[MicronasPICA]

Hi,

I have a hierachical network design using VSS as core switch/router, redundant distribution switches and access switches with multiple VLANs.

Details:

     - EIGRP (EIGRP stub on distribution switches)

     - Routed-Etherchannels (/31) between core and distribution switches

     - L2 Trunk between distribution switches (since I need VLANs on multiple access switches)

     - HSRP configured on distribution switches (HSRP active = RSTP Root)

I attached a drawing of the network.

Problem:

When I first set up this configuration, everything works.

After some time hosts can no longer reach computers outside their building.

Inter-VLAN connections inside the building are still working.
If I shut down the according VLAN i/f on the distribution switch it works again :(.
If I restart one of the distribution switches it works too......for some time :(.

I hope this discription was heplful, so you can give me a hint of what could be wrong in my config.

Thank in advance!

Best regards,
Chris

[manish arora]

What kind of links do you have between the access and distribution switches & access to access switches. To me the problem sounds like there is a  loop somewhere in you network, which is either creating broadcast strom or if you have any gaurds , it putting your gw ports ( lay man lang 0 into err-disable state.

more likely a loop.

please port conf of your distribution and access layer switches.

Thanks

Manish

[Giuseppe Larosa]

Hello Chris,

>> After some time hosts can no longer reach computers outside their building.

Inter-VLAN connections inside the building are still working.
If I shut down the according VLAN i/f on the distribution switch it works again :(.
If I restart one of the distribution switches it works too......for some time :(.

When you shut the vlan interface on D1 all users will use D2 as HSRP active device will become D2 (assuming D1 was the HSRP active device).

>> Inter-VLAN connections inside the building are still working

this would lead to problems in communication with the VSS.

I would move the devices to EIGRP full feature (unless your feature set on Di switches is limited to EIGRP stub).

Having two EIGRP stub routers that advertise the same set of IP subnets can be a problem of this design.

You should also consider the use of GLBP instead of HSRP to better use your network resources.

Hope to help

Giuseppe

[MicronasPICA]

First of all, thanks for your answers!

@manisharora111

The links are L2 trunks. I'm running Rapid-PVST which prevents loops.

@giuslar

After some further tests I think the problem is related to EIGRP having an equal cost link to the distribution switches.

Unfortunately my feature set (ipbasek9) on the distribution switches only allows me to use EIGRP stub and HSRP.

Further testing:

I raised the delay of the link VSS---D2 on the VSS, so VSS---D1 is the best path to the building.

I re-activated all VLAN i/f and configured D1 as HSRP active ---> Everything works perfectly!

If I set D2 to be HSRP active it doesn't work anymore. Why?

[kebaldwi]

Remember the EIGRP stub will not forward routes it learns from upstream routers/switches past itself... so when the distribution learns the route it drops that route before informing the other distribution switch. You could get round this with leaking the route between the stub routers but EIGRP stub by design is supposed to operate in this fashion.