Cisco 3640 can't route traffic until pinging

[ayao]

Hi,

We have a Cisco 3640 router running c3640-is-mz.123-3g.bin

Switching ports are devided into several VLans.

Each VLan has its own IP subnet.

We can't ping IP address X in subnet A from subnet B unless we log into the router and ping it from there first.

(and then the IP address will show up in "show ip arp" command.

Then we can ping X in subnet A from subnet B, and browse web on device X from subnet B, etc. )

Has anyone experienced similar situation before?

Could you let me know how to fix it?

Thank you!

-Andrew

[Reza Sharifi · Accepted solution]

Hi,

Is the default gateway configured correctly on all end device?

Do you have switch between the router and the end devices?

can you post the3640 config?

HTH

[ayao]

Hi Reza,

Thank you for replying.

The default gateway is configured correctly on all end devices.

There is no switch between router and end devices.

Sorry I can't post the config.

Thank you!

-Andrew

[Reza Sharifi]

Hi Andrew,

So, the end devices are directly connected to the 3640 router?  How many vlans and at what speed?

Any firewall application on the PC/laptops?

Reza

[Kishore Chennupati]

Is it jsut this one  X ip address of all the PC's  in that vlan having the same issue?? if not can you test another PC with the same IP address or something. i am thinking more of a PC issue than the router. After the 4 hours arp timeout on the router when it tries to send an arp again the NIC is probably nt responding back.

HTH

Kishore

[billy.williams]

Do you have ip routing turned on?

Sent from Cisco Technical Support iPhone App

[ayao]

Dear all,

Thank you for your replies!

I found out where the issue is.

This router has CEF enabled.

Somehow some IPs (mostly only listen to UDP/RTP packets) get washed out from CEF table when ARP cache expires.

After disabling CEF, everything is fine now.

I don't know why CEF behaved like this though.

Thank you!

-Andrew