I've got what appears to be an arp problem on a Cisco 2620, IOS 12.2(15)T5 on our network. It is plugged into a Catalyst 2924XL that is setup for 2 VLANs, with another router that is being used for Nat translation and bandwidth control based off of MAC (a Mikrotik, if it means anything). The Mikrotik router has 2 ethernet ports that are plugged into the Catalyst (one on each VLAN), and its default route is to the Cisco. The basic setup is as follows:
Cisco 2620--------S VLAN1
The Cisco router has an IP of x.x.x.249/29, the Mikrotik's outside address is .250/29, and the Catalyst is .252/29. Now this all worked when initially setup, the routing functioned as expected, but after a few hours, the Cisco router could not ping the Mikrotik or the Catalyst IPs, and 'sh arp' showed Incomplete for these addresses. After a 'clear arp', I could ping the .250, but not .252. I then did a 'wr mem' and 'reload', which then lost the ability to ping either device. If I did a broadcast ping (.255), I got a reply from both .250 & .252, but no entries in the arp table. However, I was able to do a static arp entry for both devices and could pass traffic to them again, but as soon as I remove the static entry, I'm back where I started (can't ping either device). Google searches show a few similar problems, and it seems that in their cases, changing the arp timeout to 5 minutes from 4 hours cleared their problems, but the cause of the problem was never discovered.
I honestly don't know where this command came from. I don't remember entering it myself, but I might have when I was adjusting arp timeouts for some reason. I've removed it ('arp arpa' on the conf-if#). It seems to be working now (arp table is still full after removing the static arps), but I'll keep a close eye (and monitoring program) on it to see if this clears it up.
Thanks Sundar, it's always good to have another pair of eyes.
Now I'm really confused. I dug up my oldest config from this router (we took over control of this network a few months back, so it was already in place), and this 'no arp arpa' was in that as well. This hasn't been a problem until recently, though. Regardless, this looks to have cleared up our problems.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...