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ayao
Beginner

Cisco 3640 can't route traffic until pinging

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

1 ACCEPTED SOLUTION

Accepted Solutions
Reza Sharifi
Hall of Fame Expert

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

View solution in original post

6 REPLIES 6
Reza Sharifi
Hall of Fame Expert

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

View solution in original post

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
Hall of Fame Expert

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

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
Beginner

Do you have ip routing turned on?

Sent from Cisco Technical Support iPhone App

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