Traceroute to a device connected to HSRP standby switch

[raghav.rai]

Hi All,

Please refer the attached diagram, I am trying to trace from 1.1.1.1 to server 4.4.4.4 my trace is showing 3.3.3.3 (HSRP standby) instead of 2.2.2.2 (HSRP Primary) as the last hop.

In my case SERVER-1 is in VLAN-1 and 2.2.2.2 is the HSRP PRIMARY router, however  the physical L2 connectivity to HSRP primary is via HSRP Secondary switch.

My expectation was that trace will show 3.3.3.3 as the last hop as L3 connectivity for this trace ends at 3.3.3.3. Any idea why 2.2.2.2 is replying to the arp request in the traceroute to 4.4.4.4?

Thanks,

Raghavendra

[chrihussey]

I understood the first two parts of your question, but the third part I found a bit confusing and contradictory,  I may be missing something but please clarify if you can.

Anyhow, with regard to the trace route from 1.1.1.1 to 4.4.4.4, HSRP has no bearing on the routing from 1.1.1.1 to 4.4.4.4 direction. The MPLS provider chose to route though the 3.3.3.3 to get to the 4.4.4.4. It's only the response from 4.4.4.4 back to 1.1.1.1 that would go back through the 2.2.2.2 since that is it's default gateway.

Hope this helps

[raghav.rai]

Hello,

Let me reframe like this..

Traffic path from 1.1.1.1 to 4.4.4.4 is like this ---

Routing ---- 1.1.1.1--->MPLS--->2.2.2.2

Switching ---> from 2.2.2.2 (HSRP Primary router) it is switched to 4.4.4.4 via he standby switch (3.3.3.3)

So expected traceroute result should be:

1.1.1.1--->MPLS--->primary CE-Router-->2.2.2.2-->4.4.4.4

But I am getting the below trace result:

So expected traceroute result should be:

1.1.1.1--->MPLS--->primary CE-Router--->3.3.3.3-->4.4.4.4

HSRP Standby switch is replying to traceroute request instead of HSRP is Primary, just wanted to know is there any technical reason for it?

Tks,

Raghavendra

[Predrag Jovic]

Since HSRP is in use - server belongs to the same VLAN as HSRP SVIs for that specific VLAN.

Active HSRP is used for forwarding traffic into MPLS cloud, but return traffic from MPLS cloud prefers standby HSRP device for return traffic (for whatever the reason). This is example of asymmetric routing.

[raghav.rai]

Thankn you  for your reply.

There is no asymmetric routing as the trace is hitting Primary MPLS CE and there is no connectivity from Primary MPLS CE to 3.3.3.3 it should come via 2.2.2.2 

[chrihussey]

Based on what you've explained, it doesn't sound like these would be the expected results.

How are the switchports configured that connect to the PE routers? Are they configured strictly as routed ports or switchports in a VLAN? 

Can you do a trace route just from the primary router to 4.4.4.4, and if you do does it show 2.2.2.2 as the next hop?