Strange PING Behavior

[visitor68]

Folks, I am stumped!

Strange Behavior.

All switches have a routed SVI for VLAN 100 (/29).

A: 10.10.100.2

B: 10.10.100.1

C: 10.10.100.3

D: 10.10.100.4

All switches have a full ARP table for all 4 SVI addresses, except for switch A. "A" only has entries for itself and its vPC partner switch B. I noticed this when A could not PING C or D. Switch A could PING B, B could PING C. Moreover, C could PING B, and B could PING A, but A could NOT PING C.

I see that Switch "A" sends out an ARP request for C when I PING C, and C responds to A. Switch A receives the ARP reply, but never seems to populate its ARP table with the information. I ran a debug to verify all this. There is a request that is broadcast to ffff:ffff:ffff and a unicast reply to A from C.

So, as a test, I entered a static ARP and mac-address table entry for C on A and now I can PING C from A. What is going on?

This is a very bare bones config. The link between B and C is a dot1Q trunk with VLAN 1 (native) and 100 allowed.

Thank you!

[visitor68]

Wow...no one? :-) Where are all the experts and geniuses on here? Seriously, would really appreciate some feedback.

Thank you

[Masoud Pourshabanian]

I do not know which brand or version of OS you are using. Just make sure you have created vlan 100 in switch A. In old Cisco IOS you need to create vlan after creating SVI.

Show vlan 100

show int vlan 100

[chris noon]

Can you do a "show version" on each of the devices and paste the result please.

im interested in the model number and the software version.

[Richard Bradfield]

Can switch D ping A an B?

[chris noon]

I have tested a scenario similar to yours and everything is working as it should.  I am interested to know what model switches you are using and what firmware you have on them.  This will make investigation a little easier.

[devils_advocate]

What model of switch are you using?

What IOS?

Can you provide the full configs?