HSRP configuration and tracking serial interface

raju · ‎02-13-2006

Hello,

We are in the process of submitting a RFP for a new requirement to one of our customer. We have two options in the design and we would like to discuss the pros and cons of this design. We have two L3 Switches (3550) and both the L3 switches are connected to edge Router as indicated in diagram. The Edge Routers have WAN links to customer and the requirement is when the serial in R1 goes down, the entire traffic should get diverted through R2 serial. One is idea is to bring both L3 Switches and both edge Routers in same HSRP group and track the R1 serial from L3-SW1. When R1 serial goes down, the traffic will get diverted through L3-SW2, then R2 serial.

The other option is configure the HSRP between only both the edge Routers (R1 & R2) and in that case we need a L2 Switch to connect both L3 and both the edge Routers. In that case, we will track the serial of R1 from RI Ethernet only and in case serial goes down, the traffic will get diverted to R2 serial. In that case both L3 switches will be in one HSRP group and both edge Routers will be in different HSRP group and we need a Layer2 Switch. FYI , We don’t want do Load balancing between both the WAN links . At any point of time , traffic will go through only one WAN link as our applications will not support load balancing.

Your thoughts are appreciated.

Regards,

Raju

devang_etcom · ‎02-13-2006

hello Mr. RAJU

hello i am devang i m not having that much experiance but i just explainig what i feel...

first of all will u clear me the logic why u need to put L2 switch as per your second diagram??? and what ever i think the first one will be better as its reduce the cost and configuration complexity ....

regards

devang

attrgautam · ‎02-14-2006

Ok I dont know how much of a problem this is but lets see. Say if the connectivity btn Sw1 and Sw2 is down. The HSRP will not flap over and the VLAN stays up. Hence traffic from Sw2 to R1 (Primary) will totally drop. For this one reason, I would suggest using Option 2. Of course if the switches are nearby then you can physically replace the cables and go with option 1. Let me know what you think of it.

nihal.akbulut · ‎02-14-2006

Hi,

why dont you think about using a dynamic routing protokol? For exapmle;

the topolgy is like your CAN1. And a dynamic routing protokol ( for example ospf) is running between your l3 switches and routers. Just as a simple area.

- put "ip ospf cost X" under the serial interface on your R2.(X must be higher than cost of R1's serial interface. you can check it with " sh ip ospf interface" command.)

- write a defalt route pointing serial link in each router . And redistribute them into ospf.

Both routers will anounce the default route to L3 switches but with different metrics. lower metric will be selected. so when two serial links are up the R1's serial will be used. When it goes down second route will be ready for use.

hope this helps